DIY Self-Watering Pots and Mini Wicking Beds – How to Build Your Own Sub-Irrigation Systems

Self-watering pots are a simple and effective way to keep plants watered with less effort. Instead of applying water to the surface of the potting medium each time a plant needs watering, these containers store water in a reservoir beneath the pot, where it is drawn upwards to the plant roots as required.

These systems have been used for decades, particularly for indoor plants. African violet growers commonly use small wick-watering pots to provide their plants with a continuous supply of moisture, while larger self-watering containers are popular for growing vegetables such as tomatoes. The same principle is also used in wicking beds, which are essentially self-watering containers scaled up to the size of a raised garden bed.

The method of watering plants from below the growing medium is called sub-irrigation. It’s quite easy to make your own sub-irrigation systems using ordinary plant pots, plastic containers and other inexpensive materials, many of which can be recycled.

In this article, we’ll look at how these systems work, how to build three different types of self-watering pots, and how to modify the larger designs to grow plants that require much wetter soil conditions.

How Do Self-Watering Pots Work?

Self-watering pots use a process called capillary action to draw water upwards from a reservoir into the growing medium above it.

Water is able to move through very narrow spaces, such as those between the fibres of a cord or the tiny pores within potting medium. Water molecules are attracted to these surfaces through a force called adhesion, and they also attract one another through a force called cohesion. Together, these forces allow water to move upwards through the narrow spaces against the pull of gravity.

When a wick extends from a water reservoir into the potting medium above it, water travels upwards through the wick and spreads into the surrounding growing medium. As plant roots absorb water, and moisture is lost from the surface through evaporation, more water moves upwards from the reservoir to replace it.

The height to which water can rise depends on the material through which it travels. Different potting mixes have different pore sizes and moisture-holding properties, so some will wick water higher than others. This becomes particularly important when constructing larger self-watering planters, where the water must travel further upwards to reach the plant roots.

The basic design is quite simple. All that’s needed is a container to hold water, a pot containing the growing medium, and a wick connecting the two. Let’s start with the simplest version, which can be made in just a few minutes.

1. How to Build a Wick-Watering African Violet Flower Pot

African violets (Streptocarpus sect. Saintpaulia) grow best when their potting medium is kept evenly moist. Allowing the growing medium to become excessively dry between waterings creates a wet–dry cycle that can adversely affect their growth and flowering.

Wick watering provides a continuous supply of moisture and avoids this damaging wet–dry cycle. This is why the method has been widely adopted by African violet growers, particularly those who maintain large collections of plants.

The system consists of a small plastic plant pot sitting above a container of water, with a synthetic cord extending from the potting medium into the water below. The cord draws water upwards, keeping the potting medium moist without requiring frequent watering from above.

Materials Required

All that is needed is a small plastic plant pot with drainage holes, a length of synthetic cord, suitable potting medium, and a plastic food container with a lid to serve as the water reservoir.

For a typical 10 cm (4″) African violet pot, use a cord approximately 15–20 cm (6–8″) long. Acrylic, nylon and other synthetic materials with an open weave work well because water can travel between their fibres. Natural fibres such as cotton eventually rot, so synthetic materials are preferable for a permanent wick-watering system.

The potting medium is also important. Use a light, porous African violet mix suitable for wick watering, containing at least 50% coarse perlite. This provides the air spaces needed by the roots while the growing medium remains continuously moist.

Construction Instructions

Step 1 – Prepare the watering wick.

Cut a length of synthetic cord approximately 15–20 cm (6–8″) long, or longer if necessary to reach the bottom of your chosen water reservoir.

Soak the cord thoroughly in water to saturate it before installation. A dry wick may not immediately conduct water effectively.

Step 2 – Thread the wick through the plant pot.

Pass one end of the wet cord through a drainage hole in the bottom of the plant pot, leaving enough cord hanging below the pot to reach the bottom of the reservoir.

Arrange the remaining length of cord inside the pot so it extends upwards through the growing medium, or winds around the inside of the pot. This keeps the wick in contact with the potting medium and helps distribute moisture around the roots.

Step 3 – Fill the pot and plant the African violet.

Fill the pot with suitable African violet potting medium, positioning the plant at the same depth it was growing previously.

The pot now has a length of cord hanging from its base, rather like a tail. This is the wick that will draw water from the reservoir.

Step 4 – Water the plant thoroughly.

Water the newly planted African violet from above to moisten the entire potting medium and wick.

This initial watering is important because capillary action works more effectively when the wick and the growing medium are already moist and in good contact with one another.

Step 5 – Make the water reservoir.

Take a clear plastic takeaway food container with a secure-fitting lid and cut a hole in the centre of the lid, large enough to allow the wick to pass through without being pinched.

You can also make a second hole near one side of the lid, through which water can be added to the reservoir without having to remove the plant pot.

Step 6 – Assemble the self-watering pot.

Fill the reservoir with water, fit the lid, and place the planted pot on top.

Thread the hanging wick through the hole in the lid and make sure it extends down to the bottom of the reservoir. This allows the wick to draw water from the reservoir even when the water level becomes low.

The base of the plant pot should remain above the water, with only the wick extending down into it.

Wick-watering system showing the plant pot supported above a water reservoir, with a synthetic cord carrying water upwards into the potting medium.

Using and Maintaining the Wick-Watering Pot

Once assembled, the system will continue supplying moisture to the growing medium as long as there is water in the reservoir and the wick remains in contact with it.

Check the water level periodically and refill the reservoir when required. The clear plastic container makes this easy because the remaining water can be seen without removing the plant.

African violet growers often add a weak fertiliser solution to the reservoir to provide a continuous supply of nutrients. Use a suitable African violet fertiliser at the recommended low concentration.

Because water continually moves upwards through the growing medium, dissolved minerals and fertiliser salts can gradually accumulate. To remove these deposits, occasionally lift the plant off its reservoir and water the potting medium thoroughly from above, allowing the excess water to drain away. Monthly flushing is a useful practice for continuously wick-watered African violets.

This simple design works very well for small pots. For larger plants, however, we can improve the system by replacing the cord with a much larger wick made from the potting medium itself.

2. How Commercial Self-Watering Pots and Planters Work

Commercial self-watering pots are available in many sizes, ranging from small indoor plant containers to large planters suitable for vegetables, shrubs and other plants.

Most use a similar arrangement, consisting of a water reservoir beneath the planting container, with a perforated barrier separating the potting medium from the water below. A filling opening or pipe allows water to be added directly to the reservoir.

The interesting part of the design is how water moves upwards from the reservoir into the growing medium.

Instead of using a cord, many commercial self-watering pots have hollow projections or ‘feet’ extending downwards from the base of the planting container. These feet are filled with the same potting medium as the rest of the pot, and have holes or slots in their sides that allow water to enter.

When the reservoir is filled, the lower portions of these soil-filled feet sit in the water. The wet potting medium inside them acts as a wick, drawing water upwards by capillary action into the rest of the potting medium above.

Because the feet contain potting medium, they form a continuous connection between the reservoir and the growing medium in which the plant roots are growing. Their larger contact area allows water to enter the potting medium through several points beneath the planter.

Commercial self-watering pot showing the planting container and water reservoir beneath it.

Top view of a commercial self-watering pot and its water reservoir.

Bottom view of the planting container showing the hollow wicking feet. The slots in their sides allow reservoir water to reach the potting medium inside them. Additional slots in the base of the planter allow excess water to drain into the reservoir when the pot is watered from above.

An important feature of this design is that the reservoir water level is controlled, so the planting container sits above the water while the wicking feet extend down into it.

The height to which water travels through the potting medium depends on its capillary properties. Water rises through the smaller spaces between particles, and the mixture of materials in the growing medium determines how far moisture can travel upwards.

This is one reason why the type of growing medium matters in self-watering planters. A suitable potting mix must be able to draw moisture upwards while also providing enough air spaces for the plant roots.

The slotted barrier also serves another purpose. When rain falls on the planter, or the growing medium is watered from above, excess water can drain through the openings in the bottom of the planting container and enter the reservoir. An overflow outlet then allows any water above the reservoir’s maximum level to escape.

Now that we’ve seen how commercial self-watering pots work, we can use exactly the same principle to make our own larger self-watering planters from recycled materials.

3. How to Build Large DIY Self-Watering Pots and Mini Wicking Beds

Large self-watering pots can be constructed from ordinary plastic plant pots, storage tubs, plastic drums and other watertight containers.

These systems work like miniature wicking beds, storing water beneath the growing medium and allowing it to move upwards to the plant roots. They are particularly useful for growing vegetables in containers and can be made in a range of sizes to suit the space available.

One of the advantages of building your own self-watering pots is that you can choose the size and shape of the containers to suit your plants. You can also make use of recycled materials that might otherwise be discarded, reducing the cost of construction.

For growing edible plants, choose clean, sturdy containers suitable for food production, and avoid containers that previously held hazardous chemicals. The containers must also be strong enough to support the weight of the potting medium and plants.

There are two ways to construct these larger systems, as shown in the diagram below.

Two DIY self-watering pot designs. The left-hand system uses a plastic tub with a lid to support several planted pots, while the right-hand system uses a large planting pot fitted over a plastic drum. Both use smaller pots filled with growing medium to wick water upwards from the reservoir.

Design 1 – Multiple Self-Watering Pots Using a Plastic Tub with a Lid

The first design uses a large plastic storage tub with a lid as the water reservoir. Several ordinary plant pots are suspended through openings in the lid, with smaller pots fitted through their bases to act as the wicks.

This arrangement allows several plants to share the same water reservoir. The number and size of the planting pots can be adjusted according to the dimensions of the storage tub.

Materials Required

You will need a strong plastic storage tub with a secure-fitting lid, several plastic planting pots, smaller plastic pots or hydroponic mesh pots to serve as wicks, a length of plastic pipe for filling the reservoir, and suitable potting medium.

You will also need a drill and an appropriate saw or hole cutter to make the openings. Bricks, small paving blocks or upturned terracotta pots can be used to support the lid if necessary.

Construction Instructions

Step 1 – Select the water reservoir and planting pots.

Choose a plastic tub large enough to hold the required volume of water and accommodate the planting pots.

The lid must be strong enough to support the weight of the pots when they are filled with moist potting medium and mature plants. If the lid is flexible or the planting pots are particularly heavy, additional support will be required.

Step 2 – Cut openings in the lid for the planting pots.

Position the planting pots on the lid and mark their locations.

Cut circular openings large enough for the pots to pass through, but small enough to prevent them from falling completely into the reservoir.

The rims of the pots should rest securely on the lid, leaving their bases suspended inside the water container.

Step 3 – Prepare the smaller wicking pots.

Each large planting pot requires two or more smaller pots fitted through holes in its base.

Choose small plastic pots with a rim or lip around their upper edge, so they can be suspended through the openings without falling through.

Cut holes in the bottom of each main planting pot to accommodate these smaller pots. The openings should be large enough for the small pots to extend downwards through the base, but narrow enough for their rims to hold them in place.

The small pots must have drainage holes or slots that allow water to enter from the reservoir. Long, narrow hydroponic mesh pots are an excellent alternative because their open mesh sides allow water to move freely into the potting medium.

Step 4 – Fit the wicking pots into the larger pots.

Insert the small pots through the holes prepared in the base of each larger planting pot.

Their rims should rest securely against the inside of the main pot, with the bodies of the small pots extending below its base.

These smaller pots will be filled with potting medium, which draws water upwards from the reservoir into the main planting pot.

Step 5 – Install the water inlet pipe.

Make a suitable opening near one side of the reservoir lid and insert a length of plastic pipe.

The pipe should extend down into the reservoir and have its upper opening above the lid, where water can be poured into it.

This allows the reservoir to be refilled without lifting the planted pots out of the container.

Step 6 – Make the overflow outlet.

The overflow is an important part of the design because it limits the maximum water level in the reservoir.

With the planting pots and their smaller wicking pots temporarily fitted into position, mark the required overflow height on the side of the reservoir.

Position the overflow outlet approximately 2.5 cm (1″) below the tops of the small wicking pots.

At this level, the upper portions of the wicking pots remain above the water, while their lower portions extend into it.

Drill a hole at the marked position. This can be left as an open overflow, or a short length of pipe can be fitted through it to direct the excess water away from the container.

Step 7 – Add supports if required.

Once filled with potting medium and mature plants, the pots can become quite heavy. Check that the reservoir lid can carry the weight without sagging or bending.

If additional support is needed, place bricks, small paving blocks or upturned terracotta pots inside the reservoir beneath the planting pots.

Position the supports so they hold up the lid without obstructing the smaller wicking pots or preventing water from circulating around them.

Plastic pots can also be used as supports, but they must be secured so they cannot move out of position.

Step 8 – Fill the planting pots with growing medium.

Fill the smaller wicking pots with potting medium, making sure it reaches right down to their bases and remains in contact with the growing medium in the larger pots.

Continue filling the larger pots with a suitable, good-quality container potting mix. The potting medium inside the small wicking pots must connect directly with the growing medium above it, forming a continuous column through which water can travel.

Moisten the growing medium thoroughly and plant the vegetables or other plants you wish to grow.

Step 9 – Assemble and fill the self-watering system.

Fit the planted pots into the openings in the reservoir lid, making sure the smaller wicking pots extend down into the water storage area.

Water the newly planted containers thoroughly from above to establish good moisture contact throughout the growing medium.

Fill the reservoir through the inlet pipe. When water begins flowing out of the overflow outlet, the reservoir has reached its maximum level.

The system is now ready to use!

Design 2 – A Large Self-Watering Pot Using a Plastic Drum

The second design uses a large planting pot sitting over a watertight plastic container or drum.

This arrangement is ideal when you want to grow a large plant in a single container. A large plastic drum can be cut in half to make the water reservoir, and the planting pot is fitted over its opening.

The wicking system works in exactly the same way as the previous design, using smaller pots extending from the bottom of the planting container into the water below.

Materials Required

You will need a large watertight plastic container or a plastic drum cut to a suitable height, a large planting pot that fits securely over its opening, two or more smaller plastic pots or hydroponic mesh pots, a length of plastic pipe for the water inlet, and suitable potting medium.

Construction Instructions

Step 1 – Prepare the water reservoir.

Select a plastic drum or other watertight container that will serve as the reservoir.

If using a large plastic drum, cut it to the required height, making sure the upper edge is reasonably level.

Choose a planting pot that is wider at the top than the reservoir opening, so it rests securely over the water container without falling inside.

Step 2 – Prepare the planting pot.

Cut two or more openings in the base of the large planting pot to accommodate the smaller wicking pots.

As with the previous design, the holes must allow the smaller pots to extend below the base while their rims hold them securely in position.

Step 3 – Install the wicking pots.

Fit the small plastic pots or hydroponic mesh pots into the openings in the base of the main planting pot.

Make sure they extend far enough below the main pot to reach into the reservoir water.

Fill the wicking pots with the same potting medium that will be used in the large planting pot, ensuring direct contact between the two.

Step 4 – Fit the water inlet pipe.

Position a length of plastic pipe down the side of the reservoir, extending from an accessible point above the planting container to the water storage area below.

This pipe allows water to be added without disturbing the planted container.

Step 5 – Install the overflow outlet.

Temporarily place the large planting pot over the reservoir and mark the overflow height on its side.

As with the first design, position the overflow outlet approximately 2.5 cm (1″) below the tops of the smaller wicking pots.

Drill the overflow hole or fit a short outlet pipe to direct excess water away from the reservoir.

Step 6 – Fill and plant the container.

Fill the large planting pot with good-quality potting medium, ensuring that the growing medium in the smaller wicking pots connects directly with the medium above.

Plant the container and water thoroughly from above to moisten the growing medium.

Fit the planting pot over the reservoir, making sure it rests securely on the upper rim, and fill the reservoir through the inlet pipe until water begins flowing from the overflow outlet.

The completed planter will now draw water upwards into the potting medium through the smaller wicking pots.

An Even Simpler Example – The Self-Watering Celery Pot

The self-watering pot shown in the photograph at the beginning of this article is a particularly simple example of the second design.

It consists of an ordinary plastic plant pot fitted snugly into a florist’s pot. These are the watertight plastic containers used by florists to hold cut flowers, essentially a large pot without drainage holes.

A short offcut of 19 mm (3/4″) polypipe irrigation tubing serves as the water inlet, allowing water to be added to the reservoir beneath the planted pot.

A single small plastic pot is fitted underneath the main planting pot and filled with potting medium, where it acts as the wick. This small pot isn’t visible in the photograph because it sits inside the water reservoir.

It’s a very simple and inexpensive construction that demonstrates how easy it is to adapt ordinary containers to make a self-watering planter.

Using and Maintaining Large Self-Watering Pots

Once a self-watering planter has been constructed and filled, it requires very little attention beyond maintaining the water supply and caring for the plants growing in it.

Checking and Refilling the Reservoir

Water is added through the inlet pipe until the reservoir reaches the overflow level. Any additional water escapes through the overflow outlet, preventing the reservoir from becoming overfilled.

The interval between refilling depends on the size of the reservoir, the number and size of plants growing in the container, and the weather conditions.

A large vegetable plant can use considerable amounts of water during hot weather, particularly when it is producing fruit. Check the reservoir regularly until you become familiar with how quickly your plants use the stored water.

If the growing medium becomes dry despite water being present in the reservoir, check that the wicking pots are properly filled and that their potting medium remains in contact with both the reservoir water and the growing medium above. Watering the planting container thoroughly from above will also help re-establish capillary action if the growing medium has dried out.

Fertilising Plants in Self-Watering Containers

Plants grown in self-watering containers still require nutrients, just like plants growing in ordinary pots.

Use a suitable fertiliser for the plants being grown, taking care not to apply excessive amounts. Because these containers retain much of their irrigation water, they also retain dissolved nutrients that would otherwise drain out of an ordinary plant pot.

As water moves upwards through the growing medium, it carries dissolved mineral salts with it. The water can evaporate from the surface or be absorbed by plant roots, leaving some of these salts behind. Over time, this can lead to a build-up of salts, particularly in the upper layers of the potting medium.

Avoid excessive fertiliser applications, and periodically water from above to help wash accumulated salts downwards and out through the overflow. The overflow water must be allowed to escape during this process.

For a more detailed discussion of growing conditions and nutrient management in wicking systems, see our article on how to build a full-size wicking bed.

4. Modifying Self-Watering Pots for Bog Plants and Aquatic Vegetables

One of the great advantages of building your own self-watering containers is that you can modify the design to suit plants with different water requirements.

The self-watering pots we’ve constructed so far use an overflow outlet to keep the water level below the main planting container. This arrangement is useful for growing a wide range of ordinary vegetables and other container plants.

But what if we want to grow plants that require permanently saturated soil, or plants that naturally grow in shallow water?

There are many useful edible aquatic and bog plants that thrive in these conditions. Examples include water chestnuts, water celery or water parsley (Oenanthe javanica), watercress, water spinach (kangkong), and duck potatoes (arrowhead).

We can grow these plants in modified self-watering containers by changing the way the overflow operates.

Making a Permanently Wet Planter

The simplest modification is to construct the planter without an overflow outlet.

When the reservoir is filled, the water level can rise into the growing medium and keep it saturated. This creates the wet conditions needed by many bog plants and aquatic marginal plants.

The container still looks like an ordinary planted pot from above, because the water is stored beneath the growing medium.

This makes it possible to grow edible aquatic plants in ordinary-looking containers without needing to construct a pond.

Adding an Adjustable Overflow for Greater Versatility

An even more useful modification is to fit a tap or valve to the overflow outlet.

With the tap open, the reservoir operates as a normal self-watering container. When the water reaches the overflow level, any excess drains out, keeping the water level below the main growing medium.

With the tap closed, water can be added until the reservoir fills and the water level rises into the growing medium. The container can then be maintained in a saturated condition for aquatic marginal plants or bog plants.

Opening the tap again allows excess water to drain away until the reservoir returns to its normal operating level.

This simple modification allows the same container to be used in different ways, depending on the types of plants you wish to grow.

Note: Cover water inlet and overflow openings with fine mesh to prevent mosquitoes from entering the reservoir.

Reusing the Overflow Water

Another useful feature of DIY self-watering planters is that the overflow water doesn’t have to go to waste.

A short pipe can be fitted to the overflow outlet to direct excess water into another garden bed, a nearby plant pot, or a water filtration reed bed.

This can be particularly useful when several containers are arranged together, allowing excess water from one container to be directed where it can still be used.

The designs can be adapted in many ways using the materials available, which is one of the great benefits of making your own gardening equipment.

In Summary

Self-watering pots and mini wicking beds are simple irrigation systems that use capillary action to supply water to plants from a reservoir beneath the growing medium.

A small wick-watering pot can be made in just a few minutes using a plant pot, some synthetic cord and a plastic food container. Larger planters use soil-filled wicking pots instead of cord, allowing the same principle to be applied to vegetables and other larger plants.

By adding an overflow outlet, the maximum water level can be controlled, and by fitting a tap to the overflow, the design can also be adapted for growing bog plants and edible aquatic vegetables.

These DIY projects provide an inexpensive way to experiment with sub-irrigation while reusing materials that might otherwise be discarded. Once you’ve built a few of these small systems and understand how they work, it’s easy to apply the same principles on a larger scale.

For a much bigger project, have a look at our detailed guide on Wicking Bed Construction – How to Build a Self-Watering Wicking Bed, which explains how to construct a full-size raised garden bed using the same basic principles.

References

African Violet Association of Australia. (n.d.). Growing and flowering African violets. https://africanviolet.org.au/growing-african-violets.html

African Violet Society of America. (2020). Watering African violets. https://africanvioletsocietyofamerica.org/learn/violets-101/2146-2/

National Parks Board, Singapore. (n.d.). Oenanthe javanica. https://www.nparks.gov.sg/florafaunaweb/flora/4/9/4982/

Townsville City Council. (n.d.). Wicking bed. https://www.townsville.qld.gov.au/__data/assets/pdf_file/0022/82354/WickingBed-FS.pdf

University of Maryland Extension. (2023). Mineral and fertilizer salt deposits on indoor plants. https://extension.umd.edu/resource/mineral-and-fertilizer-salt-deposits-indoor-plants

University of Maryland Extension. (2024). Self-watering containers. https://extension.umd.edu/resource/self-watering-containers

Victoria Department of Health. (2022). Keeping your rainwater tank safe from mosquitoes. https://www.health.vic.gov.au/sites/default/files/2022-11/Keeping-your-rainwater-tank-safe-from-mosquitos.pdf

Self watering pots that wick water upwards from a water reservoir below have been around for decades. They’re commonly used for indoor plants, and they also have more specialized applications in the form of tiny wick watering pots used by African Violet growers. More recently, large DIY self-watering pots have been finding favour amongst tomato growers, and the latest self-watering trend to sweep the gardening world is that of wicking beds, self-watering pots scaled up to the size of a big raised garden bed.

The system of irrigation used in self-watering pots and wicking beds, where watering is carried out from below the soil and wicks upwards is called sub-irrigation.

In this article we’ll be looking at how to build a few different small scale sub-irrigation systems, from small self-watering pots to mini wicking beds.

1. An Introduction to Sub-Irrigation – How to Build a Wick Watering African Violet Flower Pot

This system is used because it provides constant moisture and avoids the wet-dry cycle which is damaging to African violets.

The design is very simple, and it only takes a few minutes to construct a water wicking African violet pot.

1. Take any appropriate material that will wick water to use as your watering wick
   
   (you can use a piece of cord approximately 15-20cm (6-8”) long made of synthetic material (natural materials will rot) such as acrylic or nylon with an open weave to conduct water).
2. Soak the wick thoroughly in water so it is saturated, then thread it through a hole at the bottom of a plastic plant pot, and leave a reasonable length winding around inside the pot to distribute moisture evenly to the roots.
3. Fill with potting medium and plant up with your moisture-loving plants such as an African violet.
   
   You will now have a planted pot with a ‘tail’.
4. Water the plant well to evenly wet the potting medium and wick so it will all conduct water well by capillary action when you place the wick in the water reservoir.
5. To construct the watering reservoir, take a clear plastic take-away food container, and make a hole in the lid. You can make a second hole in the lid near one side if you wish so you can refill the container with water without lifting the pot off to do so.
6. Fill the reservoir with water, sit the pot on top of it, and make sure the wick touches the bottom of the water container so it can access all the water inside.

With self-watering pots the wicking system can be made even more efficient than the simple cord wick, and the containers can be scaled up in size to accommodate much larger plants. In the next section we’ll look at the design used in commercial self-watering containers, and how we can adapt their design to construct our own DIY large-scale self-watering pots.

2. Larger Scale Sub-Irrigation Theory – How Commercial Self-Watering Pots and Planters Work

Commercial self-watering pots and planters are available in a range of sizes from the smallest indoor plant pots to very large tubs and planters able to support large or numerous plants. These pots have a side opening or a tube where water is added to the reservoir, and they utilise a slotted barrier that separates the water from the potting medium. The barrier has hollow ‘feet’ that are also filled with the potting medium and these ‘feet’ sit in the water.

The clever part of the design is that the ‘feet’ have holes or slots in the sides allowing water in, so the wet potting medium extending down into the ‘feet’ acts as a wick and carries the moisture up into the rest of the potting medium as high as the potting medium material will allow.

Self watering pot and its water reservoir, top view.

Self watering pot and its water reservoir, showing how they fit together. Note the slots in the hollow ‘feet’ to allow water to wick up into the potting medium. There are also slots in the soil barrier (bottom of the pot) to allow water to drain into reservoir if watered from above.

Now that we’ve seen how commercial self-watering pots work, we can design and build our own to suit our requirements!

3. How to Build a DIY Large Self Watering Pot – Mini Wicking Bed System

Very large DIY self watering pots can be constructed from large plastic tanks cut in half or plastic containers with lids, as shown in the diagram below. These function as small wicking beds that you can grow quite a few plants in, and they have the additional benefit in that they’re fairly easily movable. Additionally, they can be modified very easily to grow a wider range of plants than the self-watering pot that you buy off the shelf.

If you’re into sustainable gardening, the great thing about these DIY self-watering pots is that you’ll make them mostly, if not completely, from recycled materials!

The design is quite self-explanatory, we have two designs here, side by side:

1. With the design on the left, a plastic tub with a lid holds the water. Holes are cut into the lid so plastic pots can fit into the holes (but can’t fall though!)The pots have holes cut into their bottom to fit two or more smaller pots that once again can fit into the holes (but can’t fall though!) It helps if these smaller pots have a lip to help hold them in place. These smaller pots act as the wicks and conduct water up into the pot. In place of these small pots you can also use the long, narrow mesh pots used in hydroponic systems.Make sure the lid is strong enough to hold the weight of the pots filled with potting mix and with plants in them. If required, you can use something under the post to hold them up, such as bricks or small pavers, or upturned terracotta pots. Plastic pots can be used but they need to be secured so they don’t move around.
2. With the design on the right, a large container or plastic drum cut in half to hold water. A pot that is wider at the top than the water container fits in snugly to seal the system, and uses smaller wicking pots identical to the system discussed above.

Both these designs have a water overflow outlet to prevent them flooding. You can simply cut or drill a hole on the side of the water container, or a make a hole and insert a small pipe if that’s more useful to direct the overflow water. Position the overflow outlet about 2.5cm (1”) below the tops of the small wicking pots, so the tops of the small wicking pots are always above the water.

These DIY large self-watering systems are used successfully by tomato growers and can be used for growing quite a variety of vegetables. Experiment and see what works best!

In case you’re wondering, the self-watering pot pictured at the beginning of the article growing celery is simply a plastic pot that fits snugly into a florist’s pot (what they use in florists shops to hold cut flowers, basically a pot without holes, or a bucket without a handle), with an offcut of 19mm polypipe irrigation tubing as a water inlet, and a single small pot underneath it all, which you can’t see, to wick the water upwards.

Modifying the Design for a More Versatile Pot

You can also modify the design of these larger DIY self-watering pots to grow a wider range of plants such as those that require a much wetter soil. Some plants that can grow in very wet soil are aquatic marginal plants and bog plants. This includes a lot of edible aquatic plants such as water chestnuts, water celery, water parsley, watercress, water spinach (kangkong), duck potatoes (arrowhead) and many others.

The modification is quite simple – if don’t put in an overflow hole it will flood and stay wet, but look like a regular plant in a pot without any standing water that will attract mosquitoes.

To make the design more flexible, you can put a tap in the overflow so you can use it with the tap open for plants with regular water requirements and with the tap closed so it floods for water and bog plants.

If you’re into saving water, you can direct the water from the overflow pipe into garden beds, other pots, water filtration reed beds, wherever you like. The great thing about DIY projects is that you can get creative as you like!

In Summary…

In this article we’ve explored the theoretical aspects of sub-irrigation, explaining how it works, and the practical side of how it can be implemented, looking at how to build a few small to medium-sized sub-irrigation systems that are cheap, quick and easy to put together. These projects are a great way to start experimenting with sub-irrigation without investing too much money, time and effort.

If you’ve tried these and want to try something much bigger, then please have a look at our article on how to design and construction of full-size wicking beds.