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How to Build a Small Water Garden

Angelo (admin)
waterlily

A reflective pool has a natural attraction in a garden. Water adds movement, reflections and sound, and even a small body of water creates a habitat that is completely different from the surrounding soil and vegetation.

Many garden water features consist mainly of a decorative structure with water flowing through it. A water garden is different because the plants and other aquatic life are the main feature. It is a small aquatic ecosystem, with plants occupying the surface, shallow margins and submerged space below.

A full-sized pond requires considerable space and construction, but a small water garden can be made in almost any large watertight container. A wooden wine barrel cut in half, a rigid plastic half-barrel liner, a large glazed pot or another container of similar size can be transformed into a water garden in an afternoon. This makes container water gardens particularly useful in small urban gardens, courtyards and patios where there is no room for a conventional in-ground pond.

Water gardens also have a useful place in a permaculture garden. They introduce an aquatic habitat that can support insects and other wildlife, provide somewhere to grow aquatic and edible water plants, and, where the volume is sufficient, can support fish. Larger and more specialised aquatic systems can also be used for aquaculture and conservation work with aquatic species.

Aquatic systems can be highly productive because water and dissolved nutrients are continuously available to the plants. Aquatic plants absorb nutrients from the water and sediment, animals return nutrients through their wastes, and microorganisms break down dead organic material so that its nutrients become available again. A well-established water garden therefore functions as a living nutrient-cycling system rather than simply as a container filled with water.

How a Small Water Garden Works

A successful water garden combines plants that occupy different parts of the aquatic environment. For practical water gardening, these plants can be divided into four main groups: rooted floating-leaved plants such as water lilies, marginal plants that grow in shallow water around the edge, submerged plants that grow mainly below the surface, and free-floating plants that live on the surface without being rooted into soil.

Each group uses a different part of the available space and performs different functions. Floating leaves shade the water and provide overhead cover. Submerged and free-floating plants take dissolved nutrients directly from the water. Marginal plants provide height and dense cover around the edge. Their stems, leaves, roots and pots also provide surfaces on which algae, bacteria, fungi and other microorganisms establish thin biological films. These microorganisms help break down organic material and recycle nutrients within the water garden.

Submerged plants are often called oxygenating plants because their green tissues release oxygen while photosynthesising. They also respire and consume oxygen, however, so their role is much broader than simply adding oxygen. They absorb dissolved nutrients, provide underwater shelter and create a large surface area on which microscopic aquatic life can live.

This arrangement is also an aquatic example of the permaculture principle of stacking, where several layers occupy the same horizontal area. A forest garden is commonly described as having canopy, low-tree, shrub, herbaceous, rhizosphere, groundcover and climbing layers. A water garden uses the same principle in a different environment: marginal plants occupy the shallow edge and extend above the water, floating plants occupy the surface, rooted floating-leaved plants connect the soil or sediment below with the surface, and submerged plants occupy the water column. This vertical layering allows a surprisingly diverse collection of organisms to live in a very small area.

Planning a Small Water Garden

Before buying plants or filling the container, decide where the water garden will be located, what container will be used, how the different planting depths will be created and whether fish will be included. These decisions determine how much usable water the system will contain, what plants can be grown and how easy the finished water garden will be to maintain.

Choosing a Container

Almost any large vessel can become a water garden if it is watertight, structurally sound and deep enough for the plants being grown. Suitable containers include wooden half wine barrels fitted with pond liner, rigid plastic half-barrel liners, large glazed ceramic pots, fibreglass or resin containers, troughs and other large watertight tubs.

The water garden shown in this article uses a rigid plastic half-wine-barrel liner with a capacity of approximately 100 litres (26 US gal).

A broad container is generally more useful than a tall, narrow one because water lilies and other floating-leaved plants need surface area in which to spread. Greater depth is still useful because it allows plants to be placed at several levels and increases the volume of water, which slows temperature changes. The most useful container therefore provides both adequate surface area and enough depth to create several planting zones.

If a real wooden half barrel is used, fit it with a proper pond liner or rigid insert. Old barrels may leak when the timber dries and contracts, and a liner isolates the water from residues that may remain in the wood. The liner should be supported across the base rather than hanging from the rim once the barrel is full.

Large glazed ceramic pots can also make excellent water gardens. Any drainage hole must be sealed completely before use, and the container should be filled and left long enough to confirm that it does not leak before plants are installed. Unglazed terracotta is porous and normally needs to be sealed or lined if it is to hold water permanently.

Whatever type of container is chosen, avoid using one that previously held pesticides, solvents, fuels, oils or other materials that may contaminate the water. If fish will be included, clean the container with water rather than household detergents so that no detergent residue remains.

The weight of a filled water garden also needs to be considered. Water weighs approximately 1 kg per litre (8.3 lb per US gal), so a 100 litre container holds around 100 kg (220 lb) of water before the weight of the container, bricks, soil, gravel and plants is included. A completed half-barrel can therefore weigh well over 120 kg (265 lb). Position it on a solid, level surface before construction begins because it will be extremely difficult to move afterwards.

Choosing the Location

The location affects plant growth, water temperature, evaporation, algae growth and the amount of maintenance the water garden requires. Most aquatic plants grow well with several hours of direct sunlight each day. Around 3–5 hours of direct sun is enough for many species, although water lilies generally flower more freely with stronger light.

In warm climates, a useful position is one that receives morning sun but has some protection from intense afternoon heat. A 100 litre container heats much more rapidly than a large pond, particularly when it is dark-coloured and positioned against a heat-reflective wall or paving. This becomes especially important where fish are present because warm water contains less dissolved oxygen than cooler water, while fish and microorganisms continue consuming oxygen.

Avoid placing the water garden directly beneath a heavily shedding tree unless fallen leaves can be removed regularly. A few leaves cause no problem, but large quantities sink, decompose and add nutrients and organic matter to a very small volume of water. Deciduous trees can be particularly troublesome in autumn when most of their leaves fall over a short period.

The container should also remain easy to reach. Dead water-lily leaves will need to be removed, floating plants thinned, marginal plants divided, water topped up and pumps cleaned. A water garden tucked into an inaccessible corner may look attractive but will be unnecessarily difficult to maintain.

If a fountain or pump will be fitted, position the container where the pump can be powered conveniently and where the equipment remains accessible for cleaning. A small solar pump can be useful where only daytime circulation or fountain operation is required and running electrical power to the water garden is impractical.

Planning the Different Planting Depths

A container water garden has a single water surface, but the plants within it require different depths. A water lily may need its growing point 15–30 cm (6–12 in) below the surface, while a marginal plant may need only a few centimetres of water over its crown. Submerged plants may sit near the bottom and free-floating plants require no pot or support at all.

The simplest solution is to build underwater shelves from clean bricks, pavers or inverted pots. Deeper plants remain on or near the bottom while marginal plants are raised much closer to the surface.

Planting depth is measured from the crown or growing point of the plant to the final water surface, not from the bottom of the water garden. The height of the plant pot therefore has to be taken into account as well as the height of the supporting bricks.

It is easiest to work out the arrangement while the container is still empty. Put the plant pots in position, stack the required supports beneath them and use a ruler or measuring tape to determine where each plant crown will sit relative to the intended water line. This is far easier than repeatedly lifting saturated pots and bricks after the container has been filled.

Leave space between the pots because water lilies spread sideways across the surface, marginal plants develop larger clumps and floating plants multiply rapidly. A water garden that looks completely full on the day it is assembled will soon become overcrowded.

Bricks and pavers also displace water, which is particularly important where fish will be kept. A nominal 100 litre container may hold considerably less than 100 litres once it contains several large pots, soil, gravel and a stack of solid masonry. Use only as many supports as are actually needed.

How Much Plant Cover Is Needed?

A traditional starting rule for ornamental water gardens is approximately one water lily or other rooted floating-leaved plant, three submerged plants and one or two marginal plants for each 1 square metre (10.8 sq ft) of water surface. This is only a starting proportion because plants differ enormously in mature size. One large water lily can occupy more surface area than several miniature cultivars.

Surface coverage is therefore a more useful guide as the water garden matures. For a mixed water garden, aim for approximately one-third to one-half of the surface to be covered by water-lily leaves and other floating vegetation while leaving substantial open water.

The covered area shades the water, limits excessive sunlight and gives fish and aquatic animals overhead shelter. The open area allows light to reach submerged plants, permits unobstructed gas exchange and prevents floating plants from forming a continuous mat.

This does not require measuring the surface precisely. If virtually all the water has disappeared beneath duckweed, azolla or water-lily leaves, thin the plants. If the entire surface remains exposed to hot summer sun, more floating cover may be useful.

Deciding Whether to Include Fish

A water garden does not require fish. A plant-only container can develop into a diverse aquatic habitat, and dragonflies, damselflies and other aquatic insects may colonise it naturally.

Fish change the system because they consume food, produce waste and use oxygen. Their wastes eventually become nutrients available to plants, algae and microorganisms. A lightly stocked, well-planted container can process a modest amount of this material, but an overcrowded or heavily fed water garden accumulates nutrients much more rapidly.

If fish are planned, preserve as much actual water volume as possible, leave open swimming space, provide shaded areas and underwater refuges, avoid excessive fertiliser and do not overfeed them. A larger volume of water is easier to manage because temperature, oxygen concentration and waste levels change more slowly. A 100 litre half-barrel is therefore better suited to a small number of small fish than to species that become large.

Choosing Plants for a Small Water Garden

The four main aquatic plant groups can now be considered in more detail. The aim is not to collect as many species as possible, but to combine plants that occupy different levels and remain proportionate to the size of the water garden.

1. Rooted Floating-Leaved Plants

Rooted floating-leaved plants, sometimes called deep-water plants, have their roots or rhizomes anchored in soil beneath the water while their leaves grow upward to the surface.

Water lilies (Nymphaea spp.) are the best-known examples. Lotus (Nelumbo spp.) occupy a similar position in the pond but normally hold much of their foliage above the water instead of floating it directly on the surface.

Their leaves perform several useful functions. They shade the water, reduce heating beneath them and limit some of the light available to algae. They also provide cover under which fish and other aquatic animals can shelter.

Many rooted floating-leaved plants also produce spectacular flowers. Water lilies generally flower best in good sunlight, and dwarf cultivars are particularly useful in container water gardens because full-sized varieties can rapidly overwhelm a half-barrel.

Water lilies prefer still or gently moving water. They should be kept away from fountain spray because continuous splashing interferes with the leaves resting normally on the water surface.

Water-lily leaves and flowers are continually replaced. Remove yellow, brown and decaying leaves before they sink because decomposing foliage releases its nutrients back into the water.

Examples of rooted floating-leaved and deep-water plants include:

Large lotus and Victoria lilies belong to this plant group but are far too large for a small half-barrel. For container water gardens, choose compact species and dwarf cultivars.

Water lily

Lotus

Water poppy

Nardoo

2. Marginal Plants

Marginal plants grow in the shallow edges of ponds, lakes and wetlands. Their roots and lower stems remain wet or submerged while most of the foliage grows above the surface.

In a container water garden they are normally grown in pots raised on bricks or pavers so that the crown sits at the appropriate depth. Many commonly grown marginal plants tolerate around 5–10 cm (2–4 in) of water above the crown, although the correct depth depends on the species.

Marginal plants usually prefer still or slowly moving water. They add height and colour, soften the edge of the water garden, provide shade and wind protection and create cover for fish, frogs and aquatic insects. In larger ponds they also create the transition between open water and the surrounding terrestrial vegetation.

Suitable marginal plants include:

Yellow flag iris

Lizard’s tail

Pickerel rush

Aquatic mint

Vietnamese mint

Dwarf papyrus

3. Submerged Plants

Submerged plants grow mainly below the surface. Some root into soil or sediment while others remain unattached in the water.

They are often called oxygenators because they release oxygen during photosynthesis, but their importance does not depend on that process alone. They also absorb dissolved nutrients, provide food and shelter for aquatic animals and create a large underwater surface on which microscopic organisms can live.

Fine or divided leaves are particularly useful habitat for tiny aquatic animals and microorganisms. These form part of the food web and in turn provide food for larger organisms. Some fish also graze submerged plants, and vigorous species generally tolerate this because they can replace the lost growth rapidly.

Submerged plants can eventually become so dense that they fill much of the available water volume. Thin them when necessary and compost the excess. Removing the plant material also removes the nutrients contained within it from the water garden.

Different submerged plants grow in different ways and should not all be treated as bunches of stems pushed into gravel. Species such as Elodea and Egeria can root into substrate and grow upward through the water. Anacharis or Brazilian waterweed (Egeria densa) has dark-green stems with numerous narrow leaves, while Canadian pondweed (Elodea canadensis) has a similar submerged growth habit.

Hornwort (Ceratophyllum spp.) is different because it does not produce true roots. It can remain freely suspended in the water and does not need to be planted into soil or gravel.

Some aquatic plants grow substantially below the surface while also producing stems or leaves above it. Examples include variable water-milfoil (Myriophyllum variifolium), other Myriophyllum species and water primrose (Ludwigia peploides).

Examples traditionally grown as submerged plants include:

Anacharis

Hornwort

Variable water-milfoil

Water primrose

4. Floating Plants

Free-floating plants live on the water surface without being rooted into soil. Their leaves remain at or above the surface while their roots hang directly into the water.

Because the roots are in direct contact with the surrounding water, these plants take up dissolved nutrients efficiently. They also shade the water, so they can limit excessive algal growth both by reducing available light and by competing for nutrients. Floating plants provide additional shelter for fish and other aquatic animals.

Duckweeds (Lemna spp.) are tiny floating plants that reproduce very rapidly. They contain relatively high levels of protein and are readily eaten by fish such as goldfish. Where duckweed grows strongly, it can be harvested regularly rather than allowed to form a continuous surface layer.

Azolla (Azolla spp.) is a small floating aquatic fern associated with nitrogen-fixing cyanobacteria. This relationship allows the association to obtain nitrogen through biological nitrogen fixation. Azolla can multiply extremely rapidly under favourable conditions, and surplus material can be composted or added to a worm farm so the nutrients accumulated in its tissues are returned to the garden.

Examples of floating plants include:

Duckweed

Azolla

Water hyacinth

Water lettuce

Materials Required

Once the container, location and plants have been selected, gather the materials before beginning construction.

For the water garden itself you will need:

A bucket for keeping aquatic plants wet, a ruler or measuring tape for checking planting depths and a hose or watering can are also useful. If a fountain will be installed, have the pump and tubing available before arranging the plants so that its position can be incorporated into the layout.

A plastic half-barrel liner and solid paver bricks.

For potting the aquatic plants you will need:

Plants, plastic pots, garden soil, pea gravel and newspaper.

Aquatic plants can dry out rapidly when removed from water, particularly plants with delicate submerged foliage and water-lily leaves. Keep all plants shaded while working. Marginal plants can stand in shallow water, while water lilies and delicate submerged plants should remain completely wet in a bucket or tub until they are planted or positioned.

What Soil Should Be Used for Aquatic Plants?

Use a heavy mineral garden soil containing clay. Heavy soil remains in place underwater and provides a stable rooting medium.

Do not use ordinary potting mix. Potting mixes contain lightweight ingredients such as composted bark, peat, coir, perlite or vermiculite that can float out of the pot and cloud the water. Compost and manure are also unsuitable as the main potting medium because large quantities of decomposing organic matter release nutrients into the water and can colour it brown.

Excessive nitrogen and phosphorus stimulate heavy algal growth. When large quantities of algae or other organic material later die and decompose, microorganisms consume dissolved oxygen while breaking them down. Oxygen concentrations can fall sufficiently to stress fish and other aquatic animals. This nutrient enrichment and its consequences are referred to as eutrophication.

Plants that require supplementary feeding are therefore best fertilised by placing aquatic fertiliser tablets or another suitable controlled-release fertiliser deep inside the soil rather than leaving fertiliser exposed at the surface.

How to Build the Water Garden

Construction consists of preparing the container, potting any plants that require repotting, creating underwater planting levels, arranging the plants, filling the container and then allowing the system to establish.

Step 1 – Position and Prepare the Container

Place the empty container in its final position on a solid, level surface and check that it does not rock. Correct any unevenness before filling rather than trying to level a water-filled barrel after it contains more than 100 kg of water and materials.

Add a small amount of water first and check the container for leaks. Pay particular attention to the sealed drainage hole in a converted ceramic pot and to the folds and edges of a pond liner. If a rigid liner is used inside a barrel, make sure its base is fully supported.

Rinse bricks and pavers to remove soil and dust before putting them into the container. If a pump will be installed, decide where it will sit before arranging the plants so that it remains accessible for cleaning without requiring the whole water garden to be dismantled.

Step 2 – Pot the Aquatic Plants

Plants already growing in suitable aquatic pots do not need to be repotted merely because they are moving into a new water garden. The complete pot can simply be positioned at the appropriate depth.

Repot plants when their existing container is unsuitable, when they are being divided or when they have become badly overcrowded. Aquatic plants recover most rapidly from root disturbance while they are actively growing, so in a temperate climate major repotting is best done from late spring through summer. An established plant that remains undisturbed in its existing pot can be moved from one pond to another at any time, including during dormancy.

Potting Marginal Plants

Marginal plants can be grown in ordinary plastic nursery pots or aquatic baskets. Dark pots are useful because they become less conspicuous underwater.

Use one species per pot. Several plants or divisions of the same species can be planted together to make a fuller clump, but different species sharing a small pot eventually compete for the same limited root space and the strongest grower may overwhelm the others.

A pot around 15 cm (6 in) wide is suitable for many small marginal plants used in a half-barrel water garden. Larger plants may require containers around 20 cm (8 in) wide or larger.

1. Line the Pot

Select a suitable plastic pot. If the drainage holes are large enough for soil to wash through, line the inside with newspaper approximately two-thirds of the way up.

The newspaper temporarily holds the soil in place when the pot is submerged. It does not need to remain intact permanently because by the time it decomposes, the soil and roots have settled together.

2. Add Soil and Position the Plant

Fill the pot approximately one-third to one-half full with heavy garden soil. If the plant requires fertiliser, push an aquatic fertiliser tablet deeply into the soil so that nutrients remain near the roots rather than dissolving immediately into the surrounding water.

Position the roots of the marginal plant in the pot.

Hold the plant at its original planting depth while filling around the roots. Do not bury the crown. The crown is the basal part of the plant from which new shoots arise. Several divisions of the same species can be planted together where a denser clump is wanted.

3. Fill With Soil

Continue adding soil around the roots and firm it gently.

Leave approximately 4 cm (1½ in) between the soil surface and the rim of the pot so there is room for the gravel top dressing.

4. Water the Pot

Water the newly potted plant gently to settle the soil around the roots.

Allow the muddy excess water to drain away. If the plant will be placed immediately into a water garden already containing fish, use rainwater or dechlorinated water for this step.

5. Wash the Gravel

The soil requires a gravel top dressing to prevent it being disturbed when the pot is submerged. Use pea gravel or small river pebbles and wash the stones first to remove soil, dust and fine particles that would otherwise cloud the water.

An easy way to do this is to place the gravel into a spare plastic pot with drainage holes smaller than the stones.

Rinse thoroughly with clean water.

6. Apply the Gravel Top Dressing

Cover the soil with approximately 1–2 cm (⅜–¾ in) of washed gravel.

Keep the gravel away from the crown and emerging shoots and leave approximately 1 cm (⅜ in) below the rim of the pot.

The marginal plant is now ready to be positioned in the water garden. Place the pot near the edge and raise it on bricks or pavers until the crown is at the correct depth. Many commonly grown marginal plants are positioned with approximately 5–10 cm (2–4 in) of water above the crown, but the correct depth depends on the species.

Potting Water Lilies

Water lilies grow from rhizomes. A rhizome is a modified stem that grows horizontally and produces roots and shoots.

Because the rhizome expands sideways, water lilies are better grown in wide, relatively shallow containers than in narrow, deep pots.

Miniature water lilies can often be grown in aquatic baskets around 20 cm (8 in) wide, while regular water lilies generally require baskets around 30 cm (12 in) wide or larger.

When a water lily is purchased already growing in a suitable aquatic basket, leave it there until the pot becomes crowded. There is no need to repot a healthy plant simply because it is being moved into a new water garden.

To pot a water lily:

  1. Select a wide aquatic basket suited to the mature size of the cultivar.
  2. Line large openings with newspaper if necessary to prevent soil escaping.
  3. Fill the container approximately halfway with heavy garden soil.
  4. Place an aquatic fertiliser tablet deeply into the soil.
  5. Position the rhizome so that the roots are covered but the crown and active growing point remain exposed.
  6. Fill around the root system with soil and firm it gently.
  7. Add a 1–2 cm (⅜–¾ in) layer of washed pea gravel or river pebbles, keeping the crown and growing point uncovered.
  8. Lower the pot slowly into the water so that the soil is not disturbed.

Place the water lily towards the centre or open side of the container so that its leaves have room to spread.

A depth of approximately 15–45 cm (6–18 in) above the crown covers the useful range for many small and medium water lilies. Dwarf and miniature cultivars are generally grown nearer the shallow end of that range, and some require only around 10–15 cm (4–6 in) of water over the crown.

Newly planted lilies can initially be placed closer to the surface. As the leaf stalks lengthen and begin reaching the surface, the pot can be lowered gradually until the plant reaches its final depth.

Other rooted floating-leaved plants are planted in much the same way, although many can be grown in ordinary dark plastic pots around 15–20 cm (6–8 in) wide rather than specialised water-lily baskets.

Planting Submerged Plants

Submerged plants do not all require the same planting method. For stem plants that naturally root into sediment, gather approximately five or six healthy stems loosely together, place their lower ends into a small plastic pot and add a small amount of heavy soil where appropriate. Cover the surface with washed gravel to anchor the stems.

Only enough of the basal stems should be buried to hold them securely. Do not bury a large length of green stem beneath gravel.

A water depth of around 15–40 cm (6–16 in) is suitable for many small submerged plants used in container water gardens. As the stems grow upward, trim and thin them if they become tangled at the surface or occupy too much of the water column.

Hornwort requires a different treatment because it does not form true roots. Simply place it into the water and allow it to remain suspended. Forcing it into a gravel-filled pot serves no useful purpose.

Adding Floating Plants

Floating plants require neither soil nor pots. Rinse newly obtained plants gently to remove loose sediment, then place a small quantity on the surface. Their roots hang directly into the water and begin taking up dissolved nutrients immediately.

There is no reason to spread them manually over the whole container. Duckweed, azolla and other vigorous floating plants multiply rapidly once conditions suit them, so starting with a small amount is sufficient. Check their coverage during warm weather and remove the excess if separate colonies begin merging into a continuous mat across the surface.

Step 3 – Create the Underwater Planting Levels

Once the plants are ready, arrange the clean bricks or pavers inside the empty container. The deepest plants go at or near the bottom, while marginal plants are raised closer to the surface. A marginal crown may be only around 5 cm (2 in) below the final water level, whereas a water lily may sit considerably deeper.

Make sure the supports are stable and support the base of each pot properly rather than balancing it on the edge of one brick.

Avoid tall, narrow towers of loose bricks that could topple while plants are being moved. A large pot that needs substantial elevation is better supported on two broad, stable supports beneath opposite sides of its base.

Place the marginal plant onto its raised shelf.

Before adding water, look down into the container and make sure there is still open water between the pots, enough room for the water lily to spread and adequate access to any pump. One advantage of keeping aquatic plants in individual pots is that their height and position can be changed later without reconstructing the whole water garden.

Step 4 – Fill the Water Garden

Fill the container slowly. Do not direct a strong stream of water straight into the planted pots because this can dislodge the gravel and wash soil into the water. Aim the hose against the inside wall, onto a clean paver or onto a shallow plate so that the force of the water is dispersed.

As the water level rises, check that the pots remain stable, the gravel stays in place and each plant reaches its intended depth. If a marginal plant is too deep, add another support beneath it. If a water lily is too shallow, lower the pot.

A small amount of suspended clay may make the water cloudy immediately after filling. Leave it alone because fine particles normally settle without intervention.

The completed water garden, with plants positioned at several different depths.

What Water Should Be Used?

A plant-only water garden can normally be filled with ordinary potable tap water. Where fish are present, water treatment is more important because municipal supplies may contain chlorine or chloramine.

Chlorine can dissipate from exposed water, but chloramine is much more persistent, so simply leaving a bucket of water standing overnight is not a reliable treatment where chloramine is used. Clean rainwater is suitable for water gardens and avoids both disinfectants. Where tap water is used in a fish-containing pond, treat it with an aquarium or pond conditioner that neutralises chlorine and chloramine before adding a substantial volume.

Small top-ups are diluted into the existing water, but repeatedly replacing large proportions of the container with untreated tap water exposes fish directly to the disinfectant.

Once fish are present, avoid complete water changes simply because the water becomes slightly cloudy or green. Replacing all the water changes temperature and water chemistry abruptly and usually fails to correct the cause of the problem.

Allowing the Water Garden to Establish

A newly completed water garden often looks sparse, which is preferable to filling every open space immediately. Aquatic plants grow rapidly once established. Water lilies spread leaves across the surface, floating plants multiply, submerged stems elongate and marginal plants expand into larger clumps. A container that looks completely full on the first day can become badly overcrowded within a few months.

During the first few weeks, several things happen at once. Fine soil particles settle, transplanted plants produce new roots, microorganisms colonise the underwater surfaces, algae respond to the available light and nutrients, and aquatic insects and other small organisms may begin colonising naturally.

Some algae during this establishment period are normal. A newly planted water garden initially has a large area of exposed water while its higher plants have not yet reached full growth or nutrient uptake. As floating leaves spread and submerged and floating plants become established, they provide greater shade and stronger competition for nutrients.

Do not respond to an early algal bloom by emptying the container, scrubbing everything clean and starting again. That removes the symptom temporarily without correcting excessive light, nutrient release or overfeeding.

If fish are to be added, allow the newly planted water garden approximately a week to settle first. Where many plants have been heavily repotted or a large amount of soil entered the water, waiting longer is useful. Add only a small number of fish initially because they begin producing waste immediately while the plants and microorganisms need time to adjust to the additional nutrient load.

Adding Fish to a Small Water Garden

Fish are optional, but they add movement to a water garden and consume mosquito larvae.

The following fish have traditionally been used successfully in outdoor water gardens in Melbourne’s cool-temperate climate:

  1. Goldfish (Carassius auratus)
  2. Rice fish or golden medaka (Oryzias latipes)
  3. White cloud mountain minnows (Tanichthys albonubes)

Goldfish

Rice fish or golden medaka

White cloud mountain minnow

Rice fish and white cloud mountain minnows remain small and can coexist in an appropriately sized water garden.

Goldfish are very different. The small goldfish sold in shops eventually become considerably larger and produce much more waste than medaka or white cloud mountain minnows. A 100 litre half-barrel is therefore far easier to manage with a small population of small fish than with adult goldfish. Do not mix very small fish with large goldfish because sufficiently large goldfish can eat them.

Fish alter the nutrient balance of the water garden because they convert food into waste. A lightly stocked system can process a modest amount of waste, but excessive feeding or too many fish can result in persistent green water or filamentous algae. Feed only as much as the fish consume promptly because food that sinks and decays becomes an additional source of nutrients just like decomposing leaves or exposed fertiliser.

Provide both swimming space and cover. Water-lily leaves and floating vegetation shade part of the surface and give fish somewhere to retreat, but the entire surface should not be covered because open water remains useful for swimming and gas exchange.

Summer heat requires particular attention because small containers warm quickly. Warm water contains less dissolved oxygen while the oxygen demand of fish and microorganisms continues. Partial afternoon shade, moderate fish numbers and gentle surface circulation all help. Fish gathering at the surface and repeatedly gulping should be treated as a sign that water temperature, oxygenation or water quality needs attention.

In other climates, choose fish suited to the local temperature range rather than assuming that species suitable for Melbourne are appropriate everywhere.

Protecting Fish From Predators

A small water garden containing fish can attract cats and fish-eating birds. Because the fish have little room to escape, useful protection combines a physical barrier above the water with cover below it.

The simplest cover for a half-barrel is rigid wire mesh cut slightly larger than the opening and secured so that a cat cannot push it aside. Pond netting can also be stretched tightly over a simple frame or hoops. Raise it approximately 15–30 cm (6–12 in) above the surface so that water-lily leaves and emergent plants can grow beneath it.

Fish also need underwater refuges. A short section of wide pipe, a terracotta drainage pipe laid on its side or a small tunnel made from stable stones can be placed on the bottom. The opening should be large enough for the fish to enter freely, and the structure should not be able to roll or collapse. Water-lily leaves and other aquatic vegetation provide additional overhead cover.

For a small container, the most useful protection therefore combines a secure mesh or net cover with floating or overhanging vegetation and one or two submerged hiding places.

Mosquito Control in a Water Garden

Standing water can provide mosquito breeding habitat, but a functioning water garden does not have to become a mosquito nursery. Mosquito larvae are easily recognised as small wriggling organisms that repeatedly rise to the water surface, so the pond can be checked periodically during warm weather, particularly where fish are absent.

Fish consume mosquito larvae readily and are often effective enough to prevent large numbers from developing. They should not, however, be added solely as mosquito-control tools if the container is too small to support them properly.

Dragonfly and damselfly larvae are also aquatic predators and consume mosquito larvae and other small animals. A planted water garden containing submerged stems and marginal vegetation provides habitat for these useful predators, which is another reason not to treat every small organism in the water as something that should be removed.

Water movement can make part of the surface less attractive to mosquitoes. A fountain or circulating pump disturbs the water where it is operating, although quiet pockets can remain between dense vegetation. A pump that switches off overnight also leaves the water still for long periods, so circulation should be treated as one part of mosquito management rather than the only control.

Dense floating growth should also be kept under control because a continuous mat of duckweed, azolla or similar plants creates sheltered still spaces between and beneath the leaves. Thin these plants before the water surface disappears completely.

Where fish are absent and mosquito larvae persist, products containing Bacillus thuringiensis subsp. israelensis (Bti) can be used. Bti produces toxins active against mosquito and certain related fly larvae when ingested. Commercial mosquito-control products containing Bti are available as granules, pellets, dunks and similar formulations. Use a product intended for standing water and apply it according to the label directions.

Making a Water Garden Frog-Friendly

A water garden can attract frogs, but a water feature and good frog habitat are not automatically the same thing.

Frogs use both the water and the surrounding garden. The pond provides somewhere to breed and for tadpoles to develop, while vegetation, leaf litter, rocks, logs and damp sheltered places around it provide cover and feeding habitat for adult frogs and newly metamorphosed froglets. Good frog habitat therefore extends well beyond the water’s edge.

A purpose-built frog pond is usually better than a deep, vertical-sided half-barrel, but a container water garden can still be made considerably more useful to frogs.

Provide Both Shallow and Deep Water

A purpose-built frog pond should not have the same depth everywhere. The edge should begin very shallow and gradually deepen towards the centre. Shallow margins provide warmer water, places for tadpoles to graze and easy access for frogs entering and leaving, while deeper water provides a cooler refuge and somewhere for tadpoles to retreat when disturbed.

For an in-ground frog pond, a broad shallow margin can grade gradually towards a deeper section around 60–70 cm (24–28 in) deep. The entire pond does not need to reach that depth because the important feature is the range of depths.

A half-barrel cannot provide a natural sloping bank, so it needs an artificial escape route. Position a firmly secured branch, piece of rough timber or stable arrangement of stones so that it extends from below the water surface to the rim and continues to a secure landing point outside. A frog entering the water should not have to climb a smooth vertical wall to escape.

Give Frogs Plenty of Plant Cover

A bare pond surrounded by paving provides water but very little frog habitat. Plant both the pond and the surrounding area densely enough to create several types of cover.

Submerged plants and marginal plants provide shelter within the water. Rushes, sedges, grasses and other clumping plants around the edge provide cover where frogs enter and leave. Low groundcover creates cool, humid shelter during the day, while taller vegetation can provide shade and protection overhead.

The surrounding plants also support insects and other small invertebrates that adult frogs eat, so a frog-friendly garden needs to support the food web as well as the frogs themselves.

Do not completely shade the pond. Some sunlight supports aquatic plants, algae and the biofilms that many tadpoles graze. Morning sun with protection from the hottest part of the afternoon is a useful arrangement.

Create Shelter Around the Pond

The habitat outside the pond is just as important as the water itself. Frogs spend much of their lives away from open water, so a pond surrounded by bare paving or exposed soil provides very little protection once they leave it.

Rocks, logs, branches, leaf litter and dense low vegetation create cool, moist crevices where adult frogs can shelter during the day and newly emerged froglets can hide after leaving the water. Leaf litter can be left beneath surrounding plants instead of clearing the soil completely bare, while low groundcovers, sedges and clumping grasses help maintain a more humid microclimate close to the ground.

Logs and rocks placed partly in and partly out of the pond can also provide useful transition points between the aquatic and terrestrial habitat. A well-designed frog pond should therefore change gradually from deeper open water into shallower planted water, then into a damp, densely vegetated margin rather than ending abruptly at a bare edge.

This transition is particularly important for newly metamorphosed froglets, which are very small when they first leave the water and are vulnerable to drying out and predation. Dense vegetation and moist hiding places immediately beside the pond give them somewhere to shelter as they begin living on land.

Keep Fish Out of a Frog-Breeding Pond

If the main purpose of the pond is successful frog breeding, do not add fish. Many fish eat frog eggs and tadpoles, and in a small garden pond the tadpoles have very little space in which to avoid them.

The half-barrel described in this article can therefore be managed in two different ways. It can be a fish water garden, where fish occupy the open water and consume mosquito larvae, or it can be developed as frog-breeding habitat, in which case the fish are omitted.

Adult frogs may still visit a fish-containing water garden to drink, hunt insects or shelter among plants, but it is much less useful as a breeding site.

Keep the Water Suitable for Frogs and Tadpoles

Rainwater is particularly useful for topping up a frog pond where it is available. Avoid allowing lawn and garden runoff to enter the pond because it may carry fertilisers, herbicides and pesticides into the water. Frog skin is highly permeable, and eggs and tadpoles are continuously exposed to the surrounding water.

Do not try to keep a frog pond sterile. A mature pond should contain algae, microorganisms, aquatic insects and other small organisms. Tadpoles of many species graze algae and biofilms, while adult frogs feed on insects and other invertebrates associated with the pond and surrounding vegetation.

Excessive fallen leaves and large accumulations of decomposing material should still be removed before they foul the water, but a biologically active pond is very different from a perfectly clean ornamental pool.

Let Frogs Find the Pond

Once suitable habitat has been created, allow local frogs to discover it. Do not stock the pond by collecting frogs, eggs or tadpoles from another pond or wetland. Moving amphibians between sites removes them from their existing habitat and can spread chytrid fungus and other diseases.

Where frogs occur in the surrounding area, a suitable pond can be colonised naturally.

Adapting a Half-Barrel for Frogs

A half-barrel intended specifically for frogs should be arranged differently from one intended for fish. Fish should be left out, and at least one secure rough branch, log or stone ramp should extend from below the water to outside the container so frogs can enter and leave easily.

One or more planted pots can be raised close to the surface to create a shallow-water area within the otherwise deep container. Marginal plants should be allowed to provide dense cover around this shallow zone, while the barrel itself should be positioned beside groundcover, sedges, grasses or low shrubs rather than standing alone on bare paving.

Rocks, logs and leaf litter placed around the outside create cool, damp hiding places and link the water garden to the surrounding terrestrial habitat. The container should receive some sunlight to support aquatic plant and algal growth, but shade during the hottest part of the day helps prevent the water and surrounding shelter from becoming excessively hot and dry.

Aquatic insects and other small organisms should be allowed to colonise naturally. These changes will not turn a vertical half-barrel into the equivalent of a large in-ground frog pond, but they will make it substantially more useful as frog habitat.

For anyone specifically wanting frogs to breed successfully, an in-ground pond with broad shallow margins, a deeper refuge area and densely vegetated surroundings remains the better design.

Frogs also call at night during the breeding season, which is worth remembering when deciding where a frog pond should be located.

Tadpole

Fountains and Small Pumps

A fountain or circulating pump is optional in a planted container water garden. Still water does not mean that the pond is biologically defective, and a plant-only container can function successfully without mechanical circulation.

A pump is useful when moving water is wanted for sound and visual effect, where fish are present and additional surface circulation is useful, or where the water would otherwise remain very still. A small submersible pump draws water through an intake and pushes it through an outlet, which can feed a bubbling nozzle, a low fountain, a short spout or simply circulate water below the surface.

The main oxygenation benefit comes from moving water across and through the surface. Surface disturbance increases gas exchange between the water and atmosphere. It does not create oxygen; it improves the transfer of atmospheric oxygen into the water.

A half-barrel does not need a large pond pump. A small adjustable submersible unit is easier to control because the aim is gentle circulation or a modest fountain rather than strong turbulence throughout the container.

Keep strong water movement away from water lilies. Their leaves perform best resting on relatively calm water rather than being continually splashed or pushed around.

The pump should not sit directly on accumulated mud or debris because the intake will continually draw sediment and plant material into the mechanism. Raise it slightly on a brick, paver or inverted pot and leave enough room to remove it later without dismantling the entire water garden.

Set a fountain low enough that almost all of its water falls back into the container. A high, fine spray loses much more water to wind and evaporation than a low bubbling fountain. A poorly adjusted fountain can lower the water level surprisingly quickly because every droplet that lands outside the container is permanently lost.

Pumps also require occasional maintenance. Algae, plant fragments and sediment gradually accumulate around the intake and reduce the flow. Disconnect the pump before removing it, rinse the intake screen or sponge and remove any plant roots or fibres wrapped around it. If the flow remains weak, inspect the impeller chamber because small pieces of debris can prevent the impeller from rotating properly.

Do not use household detergent to clean pump components that will be returned to a fish-containing water garden.

Because fountains increase evaporation, check the water level more frequently during hot and windy weather. A sudden water loss much greater than normal evaporation usually indicates that the fountain is spraying outside the container or that the container has developed a leak.

Maintaining a Small Water Garden

Once established, a small water garden requires relatively little work, but it is not maintenance-free. Plants continue growing, fallen material accumulates, water evaporates and fish add nutrients where they are present.

Regular minor maintenance prevents these normal processes from eventually turning into a major clean-up. The main tasks are keeping plants within their allotted space, removing decaying material, maintaining the water level, preventing excessive nutrient accumulation and dividing plants when their pots become overcrowded.

Managing Algae

Algae are normal components of aquatic ecosystems. The presence of some algae does not mean that the water garden has failed.

Problems arise when algae become so abundant that the water remains persistently green, long strands cover the plants or dense mats dominate the surface. Two common forms are green water, produced by large numbers of microscopic algae suspended in the water, and filamentous algae, which form visible strands and mats. Both respond strongly to light and nutrient availability.

New water gardens are particularly prone to algae because much of the water remains exposed to sunlight while newly transplanted plants have not yet reached full growth. Fertiliser may also have been added recently, soil disturbance can release nutrients and fish may be introduced before the plants are fully established.

As the higher plants grow, they shade more of the water and take up more nutrients. A temporary early algal bloom often diminishes as this competition increases.

Persistent algae usually indicate that nutrients are entering the water faster than they are being removed by plant growth and other biological processes. Common sources include exposed fertiliser, over-fertilising, overfeeding fish, excessive numbers of fish, decaying foliage, large quantities of fallen leaves, manure- or compost-rich soil and accumulated sludge.

Correct these sources first. Killing the algae without reducing the nutrient supply simply leaves those nutrients available for the next generation of algae.

Healthy floating and submerged plants can provide useful competition for dissolved nutrients, while water-lily leaves and other surface foliage reduce the amount of light entering the water. This does not mean covering the entire surface with duckweed or another floating plant; the aim is still a mixture of plant cover and open water.

Long strands of filamentous algae can be removed manually by winding them around a stick, small rake or gloved hand. This removes both the algae and the nutrients stored in their tissues. Where tadpoles or aquatic insects are present, inspect the removed material before disposing of it because small animals may be caught within the strands.

Repeated complete water changes are rarely a useful algae-control method. Fresh water does not correct excessive fertiliser, too many fish, continual overfeeding or excessive sunlight. It simply makes the water look clearer temporarily while the original cause remains.

Caring for Water Lilies

Water lilies are relatively heavy feeders and benefit from regular fertilising while actively growing and flowering.

A traditional schedule is approximately every two months during the growing season, from spring through autumn. In a cool-temperate Southern Hemisphere climate such as Melbourne, this corresponds roughly to September or October through April or May.

Push aquatic fertiliser tablets deeply into the soil near the roots. Another traditional method is to place a small quantity of controlled-release fertiliser inside folded plain paper and push it down between the soil and the side of the pot. The important point is to keep the fertiliser buried rather than allowing it to dissolve directly into the surrounding water.

Remove yellow, brown and decaying leaves before they rot. Foliage left to decompose releases the nutrients stored in the leaf tissue back into the water and can contribute to algae growth. Removing old leaves also creates space for new growth.

Water lilies eventually fill their baskets with rhizomes. Divide them when the rhizomes become badly crowded, flowering declines or the leaves begin growing over one another rather than spreading normally across the surface. Hardy water lilies often need division after several years, although the interval varies with cultivar, pot size and growing conditions.

Lift the basket during the active growing season, divide the healthy rhizomes and repot the vigorous sections into fresh heavy soil.

Hardy water lilies can survive cold winters as long as their rhizomes do not freeze solid. Where only the surface freezes, lower an elevated water-lily pot so the rhizome remains below the ice. Where a small container is likely to freeze completely, greater protection is needed. Tropical water lilies are different and cannot tolerate freezing conditions.

Caring for Marginal Plants

Remove dead stems and leaves as they accumulate. Marginal plants that are actively growing and flowering can be fertilised by pushing aquatic fertiliser tablets deeply into the soil.

Many marginal plants spread by rhizomes, offsets or expanding clumps and eventually fill their pots completely. Depending on the species and the size of the pot, division may be required approximately every 1–3 years.

Lift the pot from the water, remove the plant, separate or cut the clump into healthy divisions, remove old or weak material and repot only enough divisions to refill the original container. Return the pot to its normal depth after replanting.

The surplus divisions can be potted separately, given to other gardeners, used in another water garden or composted. One of the useful characteristics of water gardening is that established plants often produce far more planting material than was originally purchased.

Caring for Submerged Plants

Submerged plants can produce dense growth during warm weather and should be thinned when their stems begin occupying too much of the available water volume, particularly where fish need open swimming space.

Do not strip all of the submerged vegetation from the container. Leave enough to continue providing habitat and nutrient uptake.

When thinning, remove older tangled or deteriorating growth first and retain healthy actively growing material. Surplus plants can be given away or composted.

Caring for Floating Plants

Floating plants can multiply extremely rapidly. Duckweed and azolla may eventually cover an entire container if left unchecked.

Maintain approximately one-third to one-half of the surface under a combination of rooted floating leaves and free-floating plants rather than allowing the whole surface to disappear beneath vegetation.

Thin small amounts regularly rather than waiting until a thick continuous mat develops. The plants can be removed by hand, with a small net or even by using an empty plastic garden pot as a scoop.

The harvested plants need not be wasted. Duckweed can be fed to suitable fish, and azolla can be added to compost or used as food in a worm farm. In both cases, harvesting physically removes nutrients from the water and transfers them elsewhere in the garden.

Maintaining the Water Level

Water is continually lost through evaporation and plant transpiration, and a fountain increases the loss further. During cool weather the level may change slowly, while hot, dry or windy conditions can lower the level of a small container by several centimetres surprisingly quickly.

When the water garden is first filled, note the normal full water level against the side of the container. This provides a simple reference when checking later water loss.

Top up before the water level falls far enough to expose plant crowns, strand floating plants on top of pots or substantially reduce the available volume for fish.

For a plant-only water garden, simply add water slowly to restore the original level. Where fish are present, use rainwater or treated tap water for substantial top-ups. If a large amount has evaporated during hot weather, add the replacement gradually rather than pouring in a large volume that is much colder or chemically different from the existing water.

Heavy rain can produce the opposite problem and cause the container to overflow. Arrange floating plants and fish refuges so that they cannot easily be washed out over the rim. After prolonged rain, check that lightweight floating plants have not escaped and that pots have not shifted.

Removing Fallen Leaves and Organic Debris

Organic matter continually enters the water garden. Aquatic plants shed leaves, insects fall into the water, dust blows in and nearby vegetation drops foliage. A small amount is normal, but problems develop when material accumulates faster than it can decompose.

Remove fallen leaves while they are still floating because they are far easier to collect at the surface than after they sink. This is particularly worthwhile during autumn leaf fall.

Trim yellow water-lily leaves, collapsed marginal stems and deteriorating submerged growth before they decay completely. Cut dead water-lily stalks near their base and remove the entire leaf rather than leaving detached material floating in the water.

Over time, fine decomposed material accumulates between the pots and bricks as sludge. A thin layer is normal. If it becomes deep, the water remains heavily tea-coloured or disturbing the bottom releases large quantities of decaying material, a more thorough clean is useful.

Remove fish first and hold them in a large container filled with water from the pond. Move the plants into buckets or tubs so they remain wet, drain the container and remove the excess sludge.

Do not scrub every underwater surface sterile. The sides of the container, bricks and pots carry established biofilms containing microorganisms involved in decomposition and nutrient cycling. Rinse away loose debris and then reassemble the water garden.

Seasonal Maintenance

The seasonal cycle depends on climate and on whether the plants are hardy, subtropical or tropical. In warm climates, aquatic plants may remain active for most of the year, while in cool-temperate climates many slow down or become dormant in winter.

During spring, hardy water lilies begin producing new leaves, marginal plants send up fresh shoots and floating plants begin multiplying more rapidly. Remove any dead winter growth and check that pots remain at the correct depth. This is a good time to divide overcrowded water lilies and marginal plants because they are entering active growth and can establish quickly. Resume fertilising when active growth is clearly underway rather than applying fertiliser to dormant plants.

Spring can also produce a temporary increase in algae because sunlight and temperature increase before the larger aquatic plants have reached their full seasonal growth.

During summer, plant growth and evaporation are at their highest. Check the water level frequently, thin floating plants before they cover the whole surface, remove yellowing water-lily leaves and trim excessive submerged growth. Fish need adequate open water, shade and oxygen during hot weather. A container in strong afternoon sun may benefit from additional shade, while gentle pump circulation can improve surface gas exchange.

Summer is also the period when mosquito activity is usually greatest, so fish-free water gardens should be checked regularly for larvae.

During autumn, growth slows as temperatures fall and day length decreases. Reduce fertilising and stop once the plants have entered dormancy. Remove declining foliage before it decomposes in the water, and keep fallen tree leaves from accumulating on the bottom.

Autumn is also the time to decide how tropical plants and temperature-sensitive fish will be handled before winter. Do not wait until the first severe cold event before moving species that cannot tolerate low temperatures.

During winter, treatment depends on the plant. Some aquatic plants tolerate freezing conditions, hardy water lilies tolerate cold water but should not have their rhizomes frozen solid, and tropical aquatic plants require warm conditions.

Hardy water lilies lose their leaves and survive as dormant rhizomes below the surface. Where only the pond surface freezes, lower the pot sufficiently to keep the rhizome beneath the ice. Where a shallow container can freeze solid from top to bottom, greater protection is needed.

Tropical aquatic plants may need to be moved indoors or otherwise overwintered according to the requirements of the species.

Fish also vary greatly in cold tolerance. Tropical aquarium fish should be moved indoors before the water becomes too cold for them. Do not assume that a fish that survives cool autumn nights can remain outdoors through winter.

In mild or frost-free climates, winter maintenance is much simpler. Plant growth slows, fertilising and feeding are reduced, dead material is removed and the water level is maintained until active growth returns.

What to Do With Excess Aquatic Plants

A successful water garden eventually produces surplus plants. Marginal plants require division, submerged plants need thinning, floating plants require regular removal and water lilies eventually fill their baskets with rhizomes.

Healthy surplus plants can be replanted elsewhere, potted to create another water garden, given to other gardeners, used as appropriate animal feed where suitable, added to compost or used in a worm farm.

Aquatic plants are particularly useful compost material because harvesting them physically removes nutrients from the water and transfers those nutrients back into the terrestrial garden. Allow very wet plant material to drain before adding large quantities to a compost heap so it does not create a waterlogged section in the pile.

Never dispose of unwanted aquatic plants into creeks, rivers, lakes, drains or wetlands. Excess plants can be composted, used in a worm farm where suitable, replanted elsewhere, or given to other gardeners.

In Conclusion

A small water garden is one of the easiest ways to add an aquatic habitat to a garden without constructing a full-sized pond.

A watertight container, a few pots, some stable supports and a carefully chosen collection of aquatic plants are enough to create a functioning water garden in a courtyard, patio or small backyard.

The key is not simply filling a container with plants. Different plants need to occupy different depths. Marginal plants grow near the surface, water lilies occupy deeper positions and spread their leaves across the top, submerged plants fill the water column and free-floating plants live directly on the surface. Together they make use of the full vertical space.

Start with fewer plants than the finished water garden appears to need. Aquatic plants grow rapidly, and within a relatively short time the problem changes from filling empty space to controlling excess growth.

Once established, a small water garden will often produce enough surplus plants to divide, compost, share with other gardeners and use to establish additional water gardens. If you know another water gardener, there is a good chance they already have spare plants for exactly the same reason.

This means a small water garden can be constructed inexpensively, become increasingly productive as it matures and add an entirely new habitat to even the smallest garden.

References

>A serene, reflective pool has its allure, it’s something that has always drawn mankind. There is something about water that relaxes us, that makes us feel peaceful and calm. It resonates with a deep inner part of us, a part perhaps long forgotten, but the connection is still there. After all, water is the very stuff of life itself.

Water features are becoming common additions to gardens these days, almost to the point of becoming clichéd! Unfortunately, they are more often than not just lifeless statues with flowing water. A pond has a far greater attraction than a plain old water feature, as it’s literally brimming with life. Anyone who has ever seen children around a pond, especially if it has fish in it, will know what a captivating effect it can have.

Most people in an urban setting have neither the space nor the expertise to construct a full-sized pond, but that doesn’t mean they can’t enjoy the benefits of a small water garden. Water gardens in containers are easy to build, and “half-barrel” water gardens are becoming quite popular for that very reason. Using a real wine barrel cut in half, or a similar sized plastic container, a water garden can be completed in an afternoon.

Beyond mere aesthetics, a water garden has its place in a permaculture garden. It can be used to grow edible aquatic plants and fish, provide a breeding site for rare and endangered fish or frogs, and produce many other valuable outputs.

A water garden is an aquaculture system – a diverse aquatic ecosystem, one of the most productive and efficient systems around. They are far more productive than any land based systems. This is because in an aquaculture system, aquatic plants have a constant supply of water that has nutrients dissolved in it, which they can easily take up. The waste from fish and other animals in the system provide additional nutrient to the plants, making for a very efficient and productive system.

Part I – Basic Water Garden Design Theory

In any water garden or pond, one of the most basic requirements to create a stable aquatic ecosystem are the various types of plants in it, each of which plays a specific role to support and sustain aquatic life.

There are four categories of water plants that can be included in a pond to achieve perfect balance.

  1. Rooted floating plants, such as water lilies
  2. Marginal plants
  3. Submerged (oxygenating) plants
  4. Floating plants


Image source: Virginia Cooperative Extension article, Urban Water-Quality Management: Purchasing Aquatic Plants. ID 426-044

Lets have a look at the four categories of aquatic plants in detail:

1. Rooted Floating Plants

Rooted Floating Plants, also referred to as Deep Water Plants, have their roots sitting in the bottom of the pond (or in a container on the bottom of the pond) and their leaves reach up to the water’s surface. They are sun-loving plants and can survive with 10-20cm or more of water above the plant’s crown. The best known examples include Waterlilies (Nymphaea spp.) and Lotus (Nelumbo spp.).

They produce floating leaves that shade the water, which reduces the growth of algae. They also provide shade and a hiding place for fish. Many rooted floating plants also produce spectacular flowers (most species need full sun 10 hours a day for best flowering).

Place these plants away from fountain sprays, as strong water movement or splashing water inhibits water lily growth. The leaves and flowers are constantly replaced and should be removed when they die off otherwise they will rot down and create more organic matter that can algae feed off.

Examples include the following:

• Dwarf or miniature water lily (Nymphaea spp.)
• Golden club (Orontium aquaticum)
• Hardy water lily (Nymphaea spp.)
• Lotus (Nelumbo spp.)
• Tropical water lily (Nymphaea spp.)
• Victoria lily (Victoria spp.)
• Yellow pond lily (Nuphar lutea)
• Water Poppy (Hydrocleys nymphoides)
• Nardoo (Marsilea mutica)
• Water Hawthorn (Aponogeton Distachyum)


Water Lily


Lotus


Water Poppy


Nardoo

2. Submerged (Oxygenating) Plants

Submerged Plants. also called Oxygenators, grow with their roots anchored in soil, but the leaves stay underwater. Oxygenators are essential for keeping the pond healthy and the water clear. The best known examples include Anacharis (a deep green plant with many delicate leaves, which will grow in water 15cm to 150cm deep) and Hornwort (dark green grass-like leaves, need 15cm to 30cm of water above the crown).

These plants absorb carbon dioxide and release oxygen into the water, and by oxygenating the water they help it support more aquatic life such as fish and beneficial aquatic insects. They also absorb excess nutrients in the water and help purify it, which reduces the growth of algae. Oxygenators also provide food and shelter for fish. The leaves, which are usually fern-like, lacy, or hairy, provide cover for the microscopic aquatic life forms which are an essential part of a balanced aquatic ecosystem.

Oxygenators can multiply very quickly and outgrow their space if not cut back regularly. Remove excess plants and compost them, they are a great source of plant nutrients. You will notice that fish eat these plants too, and that is not a concern because they can regrow quickly, and the fish just help control their growth.

These plants are usually planted in pots that are sunk to the bottom of ponds, so they sit vertically in the water, but they can also be left to free float on the water surface horizontally, though this doesn’t look as tidy.

Examples include the following:

• Canadian pondweed (Elodea or Anacharis)
• Hornwort (Ceratophyllum)

Some of these plants are Submerged/Emergent Oxygenator Plants, that is, they grow below the water’s surface, and also above it, examples include the following:

• Variable Water-milfoil (Myriophyllum variifolium)
• Water Milfoil (Myriophyllum propinquum)
• Water Primrose (Ludwigia peploides)


Anacharis


Hornwort


Variable Water-milfoil


Water Primrose

3. Floating Plants

Floating Plants are plants that float on the water’s surface, they do do not need soil, nor to be anchored to kind of base, and they grow by extracting nutrients from the water.

They control algae in two ways. Firstly, by shading the surface of the water, they restrict the light that algae needs to grow. Secondly, they are act as natural filters to remove excess nutrients from the water, which limits the nutrients available to algae.

They also have many other useful functions. Duckweed is a protein rich food source for fish, goldfish consume it greedily! Azolla is a tiny fern which supports nitrogen-fixing bacteria just like legumes do, so it captures its own nitrogen from the air. This makes it a great nitrogen source for the compost pile or as a source of rich food for worm farms.

Examples include the following:

• Duckweed (Lemna)
• Fairy moss (Azolla)
• Water hyacinth (Eichhornia crassipes)
• Water lettuce (Pistia stratiotes)


Duckweed


Azolla


Water hyacinth


Water Lettuce

4. Marginal Plants

Marginal Plants grow in the shallow margins around the edge of a pond, and they can survive with up to 10cm of water over the plant crown. These plants do best in still to slow moving water.

These plants can serve several functions. They can be decorative, adding colour and height to any shape of water garden, as well helping to blend in the edges of a pond into the surrounding ground. They also provide more practical functions, such as shelter from the wind, and shade. They also serve as a barrier around the water’s edge, providing protection to fish and frogs from predators. .

These plants are usually planted in pots, and set in shallow water on shelves or piles of bricks to achieve the correct elevation, or they can be planted directly in soil around a pond or stream.

Examples include the following:

• Arrowhead (Sagittaria spp.)
• Cattail (Typha spp.)
• Water iris (Iris laevigata)
• Water plantain (Alisma)
• Yellow flag (Iris pseudacorus)
• Lizard’s Tail (Saururus cernuus)
• Pickerel Rush (Pontederia cordata)
• Aquatic Mint (Mentha aquatica)
• Dwarf Papyrus (Cyperus papyrus)
• Horsetail Fern (Equisetum hyemale)
• Vietnamese Mint (Polygonum odoratum)
• Purple Loosestrife (Lythrum salicaria)


Yellow Flag Iris


Lizard’s Tail


 Pickerel Rush


Aquatic Mint

Vietnamese Mint

Dwarf Papyrus

Putting It All Together

Now that we’ve covered the four types of water plants, we can look at how they come together to create a balanced ecosystem.

In Permaculture the principle of stacking describes the seven defined vertical layers of a forest garden that all work together to create a balanced ecosystem, as listed below:

  1. The canopy
  2. Low tree layer (dwarf fruit trees)
  3. Shrubs
  4. Herbaceous
  5. Rhizosphere (root crops)
  6. Soil surface (cover crops)
  7. Vertical layer (climbers, vines)

In aquatic ecosystems, we have four layers that similarly work together to create a balanced ecosystem.

  1. Marginal plants
  2. Floating plants
  3. Rooted floating plants
  4. Submerged (oxygenating) plants

This too is a “stacked”” arrangement in terms of utilisation of vertical space, and when these plants are brought together with the right proportions, all the plants in that system benefit.

The rules for constructing a water garden to get the “perfect balance” are simple, as listed below.

For one square metre of pond surface area you need:

For coverage of the water’s surface:

Now, with this theory in mind we can look into building a small half-barrel water garden.

Part II – Water Garden Construction

One of the easiest water gardens to construct is a half-barrel water garden. You can literally use any watertight container of sufficient size to construct a small water garden.

In this project, we’ll use a plastic half-wine barrel liner (pictured below) for our water garden. These liners are rigid containers that can be used without putting them inside a wooden half-wine barrel, and have a capacity of around 100 litres.

Whatever container you use, make sure it is clean. A word of warning though, if you intend to put fish in your water garden, do not use any soaps, detergents or chemicals to clean the container, the residue (which won’t be detectable by you) will be present in enough quantities to kill the fish!

The construction of the water garden consists of the following steps:

  1. Gathering of materials
  2. Potting up of water plants
  3. Setting up container with “shelves” to sit plants at their correct height
  4. Filling with water!

Step 1 – Preparation, Gathering of Materials

Gather all the materials required to build the water garden.

To build the water garden itself, you will need:


A plastic half-barrel liner and half dozen solid paver bricks

To pot up the water plants that will be placed in the water garden you will need:


Plants, plastic pots, garden soil, pea gravel and newspaper

A few helpful tips:

Step 2. Potting Up Water Plants, Step-by-Step Planting

Planting usually entails removing plants from where they are currently growing and placing them in their new location. When you do this, they take some time to re-establish themselves in their new homes. So, with any replanting, keep the following in mind when deciding to build a water garden.

Now, let us look at the planting procedures for each of the four types of water plants:

A. Marginal Plants

  • Marginal plants can be planted in regular plastic pots, just make sure you plant only one type (species) of plant per pot, otherwise stronger growing species of plants will take over when they start growing.
  • You can use several of the same plant in the same pot to create a denser planting, which will have more visual appeal.
  • Use black or dark coloured plastic pots so they won’t be visible under the water.
  • A good size plastic pot that can accommodate most marginals, and that is an ideal size for a half barrel water garden id a 6” (15cm) wide pot. For larger plants you could use a 8” (20cm) wide pot.
The steps to potting up a marginal plant are as follows:

  1. Select an appropriate sized regular black plastic garden pot and line it inside with newspaper so the soil doesn’t leak out.
  2. Add soil so that the container half full.
  3. Add some fertilizer (such as Osmocote, or a water lily fertilizer tablet) into the soil at the bottom of the pot, this way it doesn’t leach out into the water.
  4. Position the marginal plant in the pot with the crown at the top and then add soil around the roots, but leave the crown uncovered.
  5. Add a 1-2cm thick layer of pea gravel or river pebbles on top of the soil to hold it in place, but once again leaving the plant’s crown uncovered.
  6. Sit the pot in your water garden or pond, at the edge, to create a border or boundary around the water.
  7. Sit the pot in your water garden or pond, at the correct height, so that there is 5cm-10cm of water above the crown of the plant (elevate the container by sitting it on bricks or pavers to achieve the correct height if necessary).

B. Water Lilies

Water lilies grow from rhizomes. A rhizome is a horizontal underground stem of a plant from which new stems and roots grow. These rhizomes spread quite rapidly, so water lilies are planted in low and wide round or rectangular aquatic basket pots (pictured below).

  • Miniature water lilies are planted in medium sized (20cm) aquatic basket pots.
  • Regular sized water lilies are planted in large sized (30cm) aquatic basket pots.
  • You won’t have to worry about aquatic basket pots unless you are propagating your own water lilies – when you buy a water lily it comes in the correct sized pot, and all you do is sit it at the bottom of your water garden or pond.
  • Lilies can be introduced into your water garden or pond from spring until early autumn.
The steps to potting up a water lily are as follows:

  1. Select the correct sized aquatic basket pot and line it inside with newspaper so the soil doesn’t leak out.
  2. Add soil so that the container half full.
  3. Add some fertilizer (such as Osmocote, or water lily fertilizer tablets) into the soil at the bottom of the pot, this way it doesn’t leach out into the water.
  4. Position the lily in the pot with the crown at the top and then add soil around the roots, but leave the crown uncovered.
  5. Add a 1-2cm thick layer of pea gravel or river pebbles on top of the soil to hold it in place, but once again leaving the plant’s crown uncovered.
  6. Sit the pot in your water garden or pond, in the centre, or away from the edge, to give the leaves room to spread
  7. Sit the pot in your water garden or pond, at the correct height so that there is 15cm-45cm of water above the crown of the plant (elevate the container by sitting it on bricks or pavers to achieve the correct height if necessary).

NOTE: Other types of Rooted Floating Plants are planted the same way as water lilies, but you can use regular black or dark coloured plastic pots, 6-8” (15-20cm) wide instead of the fancy aquatic basket pots.

C. Submerged (Oxygenating) Plants

Submerged (Oxygenating) plants absorb their nutrients directly from the water, and as a result, require a lot less soil than other water plants, and can therefore be potted in much smaller pots.

These plants are often planted in a pot filled with gravel only, just to anchor the plants to the bottom of the water garden or pot.

The steps to potting up a submerged (oxygenating) plant are as follows:

  1. Take around five or six stems of the plant, and bunch them together
  2. Put the bottom end in a small plastic pot, and fill it with gravel or river pebbles.
  3. Sit the pot in your water garden or pond, so that there is 15cm-40cm of water above the leaves of the plant

D. Floating Plants

Floating plants just float on the water’s surface, and their roots hang into the water. These plants do not require pots or soil. Simply place these plants on the water’s surface and they care for themselves, that’s it!

How To Pot up a Marginal Water Plant

To familiarise ourselves a bit better with the actual process of potting up a water plant, we’ll step through how to pot up a marginal water plant in greater detail, in six easy steps.

1. Line the pot
Line the inside of a plastic pot about two thirds of the way up with newspaper.

This is to stop the soil from leaking out of the holes below.

2. Position plant in pot
Fill the container about one-third full of soil, then place the roots of the plant in the soil and continue to fill while holding the plant at the correct height in the pot.

Be sure not to plant it too deep. You can add several plants of the same type into a single pot if you want a fuller look.

3. Fill with soil
Add soil to the correct depth and firm down lightly, so it sits about 4cm below the rim of the pot.
Water the plant
Water the plant to settle the soil around the roots and allow excess water to drain off.

Note: If this plant will go into a water garden with fish, water with rainwater or dechlorinated water, as the chlorine in tap water irritates fishes gills.

Wash top dressing (pebbles)
To stop the soil washing out of the pot, you need to add a layer of river pebbles or pea gravel as top a dressing.

To remove any dirt or residue that might cloud or pollute the water, the top dressing needs to be washed.

One simple way to washing the top dressing stones is to put them into a pot with drain holes that are smaller than them so they can be rinsed under the tap.

Fill small rinsing pot or other suitable container with stones for washing.

Rinse top dressing under tap to wash out any dirt.
4. Apply top dressing
Cover the top layer of soil with about 2cm of river pebbles or pea gravel, stopping about 1cm below the top of the rim.

The potted plant is now ready to go into the water garden!

Step 3. Setting the Water Plants at the Correct Height in the Container

As mentioned earlier, the various types of water plants will tolerate a specific height of water above their crown. The “crown” of a plant is the point at which the stem and roots join.

As only one level of water exists in a container, we accommodate plants that need shallower water by building “shelves” in the water garden to lift them to the correct height.

Typically, marginal plants will have about 5cm of water above their crowns, and one way of elevating them is to use pavers or bricks. Ensure that the pavers or bricks are clean before putting them in your water garden.

Stack the pavers or bricks to the right height, and ensure that they are stable and support the base of the pot all way around as shown in the picture below.

Here is the marginal plant set to the chosen height, now it’s just a matter of adding the rest of the plants, and filling with water.

NOTE: If you are intending to put fish in your water garden, make sure you fill it with rainwater or dechlorinated water. The chlorine in tap water burns fishes gills!

The completed water garden, placed in the correct position, all plants placed in the container at the correct heights using pavers, and water added.

New water garden even passes inspection by the local fauna!

Additional Notes – Fish for Mosquito Control

Fish can be added to a newly built water garden to control mosquitoes, though you might give the water garden a week to settle and allow the aquatic ecosystem to stabilise before adding fish.

Various fish that work well in water gardens in Melbourne’s cold climate* are:

  1. Goldfish (Carassius auratus auratus)



  2. Rice Fish or Golden Medaka (Oryzia latipes)
  3. White Cloud Mountain Minnows (Tanichthys albonubes)

NOTE: The Rice Fish and White Clouds are both small fish and can coexist together, but don’t mix them with Goldfish, which will grow big and possible eat the smaller fish.

(*Melbourne, Australia, is considered a cold temperate climate, though we don’t usually get frost in the city)

Frogs and Tadpoles

If you wish to put tadpoles in your water garden, there is a bit more involved to turn it into a frog pond. I recommend reading up about frog ponds if this is what you intend to do, as this subject is beyond the scope of this article. Just a few brief points:

Other Useful Additions to a Water Garden

Part III – Water Garden Plant Care and Maintenance

Once you put together your water garden, it may look a bit sparse at first, as the plants may still need to grow in size to give it the look you want. Be assured that aquatic ecosystems are one of the most prolific and fast growing because of the constant supply of water and nutrient, in no time it will be possibly overgrowing.

Another point to keep in mind is that after a water garden is constructed, it takes some time to establish the right balance – it is a complex ecosystem and it has to settle in. If the water fills with algae, do not change the water, this is a normal part of the process. With enough shade from floating plants to cut out some of the light, and with the submerged pants growing and taking up excess nutrient in the water, the algae will reduce and disappear.

Each of the four types of plants will require their own particular maintenance around the year:

A. Water Lilies

Water lilies are heavy feeders, and should be fertilized every two months during the growing season (spring-autumn or September/October through to April/May) to ensure good flowering. Push a water lily fertilizer tablet into the soil near the roots, or put some slow release fertilizer granules (such as Osmocote) into a folded piece of newspaper or brown paper (this paper isn’t bleached and doesn’t contain harmful chemicals) and push it between the soil and the side of the pot.

Remove any dead or dying leaves (yellow or brown leaves) to reduce algae growth, if these are left in the water garden and rot down they will provide nutrients for algae growth. Removing old growth also helps promote new growth.

Hardy water lilies can survive in cold areas and do not need to be removed from the water as long as the water does not freeze down to the roots. If the water garden or pond is very deep, and the water lily pot is elevated, then it may be necessary to move the pot even lower to the bottom to ensure that the roots are below the level of the ice. If the water all freezes completely solid, then remove the water lily before this happens.

B. Marginal Plants

Fertilizer tablets can be pushed into the soil when the plants are flowering.

Since many marginal plants multiply by division, you will eventually need to unpot them and divide them up to thin them out a bit, then repot only some of them back into the same pot. This will probably need to be done every 1-3 years. The excess plants can then be repotted to make more plants, this is called propagation by division. Surplus plants can be given away or composted, or used to make more water gardens! With water gardening, you end up with lots of spare plants!

C. Submerged Plants

Thin out submerged plants if they become overgrown and crowded, especially if there are fish in the water garden and they have very little room left to swim around. The excess plants can be given away, or they can be composted.

D. Floating Plants

Floating plants reproduce quickly, and can cover the water’s surface.

Remember, only one third to one-half of the water’s surface should be covered with free floating and rooted floating plants. This means that any time, no more than half the surface of the water should be covered with floating plants. When they cover up more than half of the surface of the water, scoop them out by hand, with a net, or even a plastic garden pot, and give them away or compost them.

As mentioned before, duckweed makes excellent fish food, and azolla makes great food for earthworms in worm farms, so make best use of this free resource where you can.

In Conclusion…

As you can see, water gardens are quite easy to set up, and they can be set up in any container that can hold a reasonable amount of water. Once you have an established water garden, I promise you that you will have so much surplus plants that you won’t know what to do with them all !

So, if you’re lucky enough to know any other water gardeners, you’ll find that they are more than happy to give you spare plants they don’t want, and this way, you can construct your water garden for next to nothing!

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