A raised garden bed is an elevated garden bed that sits higher than the surrounding soil, or the ground that it sits on, and is usually supported by some sort of frame or enclosure, though this is not always the case.
Timber Raised Garden Bed Construction
Timber raised garden beds are built using planks of wood fastened to corner posts. The corner posts can be actual wooden posts, or short lengths of the same planks used for the sides, as shown below.
The wooden planks are screwed into the posts using long galvanised screws. It’s better to use hot-dipped galvanised screws, as these have a thicker coating of protective zinc (compared to zinc-plated screws) which prevents them rusting.
There are two steps required to build a timber raised garden bed.
- Assembly of the long side panels of the garden bed
- Attaching the short side planks to the two long side panels
The first step is to assemble the long two long side panels. Screw the timber posts to the long side planks, using two screws at each point, enuring that the edges of the post are flush with the ends of the planks. The planks should not overhang past the edge of the corner posts, nor should they be short, they should be perfectly level with each other, as shown in the diagram below.
The second step is to attach the short side planks to the long side panels to make a large box shape. It’s easier to carry out this part of the construction on a flat, level, surface if possible, to ensure that all the corners are square.
A carpenters square can be used to check that the corners are actually at 90 degrees, as they should be. Once again, use two screws at each point on each plank.
How to Attach the Sides to the Corner Posts of a Timber Raised Garden Bed
NOTE: When fastening the planks to a post, the positions of the screws must be offset on either side, otherwise they will hit each other inside the post and won’t be able to screw all the way in!
As shown in the diagram below, offset the position of the fasteners slightly higher on one piece of wood, and slightly lower on the other, so they are all spaced evenly apart.
If using a railway sleeper (railroad tie, crosstie, railway tie) that is 20cm high (which is a standard height), the way to calculate where the holes go is as follows:
Since we need 4 holes evenly space from the edges and from each other, we need to divide our given width by 5. If we do the math, 20/5 = 4cm
So, on the left hand piece of timber in the diagram, we drill the first hole 4 cm from the top.
For the next position, we can’t go down another 8cm position, because that’s where the other piece will be fastened, so we go down another 4cm again to the 12cm position from the top.
So, the left hand piece is fastened at 4cm and 12 cm positions down from the top.
Therefore, the right hand side piece must be fastened at the 8cm and 16cm positions down from the top.
It’s just a matter of marking where the holes go, drilling the holes, and fastening it all together with screws, coach screws or coach bolts.
- Screws can be screwed in using a cordless drill fitted with a screwdriver bit.
- Coach screws and bolts both have hexagonal heads, and can be tightened with a spanner, socket set, or socket fitted to a cordless drill.
The reason for using cordless drills is because they have a screwdriver function, which allows the user to set the amount of torque that is applied to the screw by a variable clutch. By setting the level of torque, this determines how hard or deep the screw is screwed in, without shearing the head off the screw.
If using screws or coach screws to fasten the planks to the posts:
- As mentioned earlier, use hot-dipped galvanised screws, as these have a thicker coating of protective zinc (compared to zinc-plated screws) which prevents them rusting.
- Use the right length of screws. The rule for using screws is that they should be long enough to go right through the first piece of timber (the side plank), and approximately 2/3 of the way into the second piece of timber (the corner post).
- In hard wood, it’s not possible to screw straight into the timber without either splitting the wood or breaking the screws. Test on a scrap piece of the same wood if unsure. Drill pilot holes smaller than the thickness of the screws, so they can bite into the wood. Drill only part of the way through the post, so the screws can bite more into the wood. If the pilot holes are drilled too small, it will be hard work driving the screws in.
- Helpful tip: Rub beeswax (or a bar of soap if beeswax isn’t available) over the threads of the screw to lubricate them so they screw into the wood more easily, this also prevents the heads of the screws sheared off.
If using coach bolts to fasten the planks to the posts::
- Use hot-dipped galvanised bolts, nuts and washers for corrosion resistance.
- Drill a hole slightly larger than the bolt, and drill all the way through, both the plank and the post.
- Use a washer on the inside, then screw on the nut, and tighten using a spanner or socket on both sides.
Single Level Timber Raised Garden Bed Construction Using Steel Angle Brackets
Another way is to fasten the sides of a timber raised garden bed together, if it only is one plank high, is with steel brackets.
Steel brackets attached to the outside corners can be fastened using screws, while the brackets that are used on the inside are fastened using bolts, with nuts and washers.
The diagram below shows a steel bracket used on the inside of each corner, fastened using nuts and bolts. The heads go on the outside, and the bolts extend into the inside of the bed, out of sight, preventing a snagging or tripping hazard.
Another popular type of steel bracket used in landscaping is one which has a long stem with a pointed end, shaped like the letter “T”, that is hammered into the ground.
These can be attached either inside or outside of the raised bed structure, and fastened either with screws or bolts. The long pointed end sits firmly on the ground and stabilises the structure. This is particularly important when joining two sleepers end to end.
Considerations When Measuring and Laying Out Timber Garden Beds
Before any construction begins, it’s best to draw out a plan or design with accurate measurements, as this will help avoid mistakes. Remember, building materials are not cheap, so use the old woodworkers maxim “measure twice, cut once” and avoid the wastage.
Before we do any cutting or drilling, we need to determine where the wooden beams will be laid on the ground, and how long they need to be. This is important if the space is limited by obstructions, if you’re making an allowance for paths of a specific size, or if the beds are to match up the space you’ve allocated on a design or plan.
The critical matter to consider here is that the thickness of the timber beams needs to be taken into consideration when determining the completed internal and external garden bed sizes.
This point is illustrated in the diagram below:
As is clearly visible in the diagram, the layout of the timber alters the overall dimensions. Decide whether the short or long sides will be the ones overlapping the ends, and stick with this when cutting and assembling, otherwise the final sizes of your beds either will be mismatched, or won’t fit where you intend to put them.
Toxic Treated Timber to Avoid for Raised Garden Beds Used for Food Growing
When building timber raised garden beds, there are two considerations when it comes to the choice of timber:
- the raised bed material will last a reasonable length of time as it will be exposed to the weather – heat, cold, rain and sunlight
- the raised bed material is non-toxic
Recycled Railway Sleepers
A durable material for raised garden bed construction are railway sleepers (railroad ties, crossties, railway ties), but don’t use recycled ones. Use railway sleepers are normally treated with creosote, a highly toxic and carcinogenic mixture of chemicals, oily or tar-like in consistency, most often derived from coal tar, and used for preserving wood.
Creosote will contaminate soil, and is best avoided for all garden beds. Researchers have found that children who play with creosote-contaminated soil tend to get more skin rashes than other children, so its presence is harmful.
I’ll focus mainly on timber raised bed construction here, though I’ll cover a few other methods too.
CCA Treated Pine Timber
Traditional CCA treated pine (Copper Chrome Arsenate) contains arsenic, a poison which will leach into the soil and be taken up by plants. Arsenic is persistent, being an element, it doesn’t break down, ever, and will also bioaccumulate, which means its concentration will build up to levels higher than the soil in living things.
CCA treated pine is toxic when handling or working with it, especially when drilling or cutting it as the toxic sawdust is hard to control. It’s also toxic when burnt, and should not be disposed of that way! Having toxic chemicals in the soil is not the intent of organic gardening, nor is it in the interests of your health.
Due to the arsenic scare, ACQ treated pine (Copper and Quaternary Ammonium Compound) is now being offered on the market as an alternative. It’s touted as being a new, safer type of treated pine.
Another toxic wood treatment is LOSP (Light Organic Solvent Preservative) are all toxic. Using painted timber is not a safe practice either.
Painted Timber
Paints contain a range of toxic chemicals, so painted wood should not be in contact with soil. Even boiled linseed oil contains heavy metal additives such as cobalt and manganese which are used as drying agents.
Untreated timber will eventually rot and break down, that’s what nature intends it to do. To garden organically, either preserve the timber raised beds with raw linseed oil, or use wood that has good longevity.
What is the Ideal Size for a Garden Bed?
The optimum size of a raised garden bed is 1.2m (4′) wide when accessed on both sides, or 60cm (2′) wide when accessible from one side only. The reason for a maximum width of 1.2m (4′) is a matter of ergonomics, this is the maximum width that an adult person can reach across to access the area efficiently from either side. Garden beds can be made to any length, though it is more efficient to keep them reasonably short, to save having to walk long distances around them constantly.
I’ve found that 1.2 x 2.4m (4’ x 8’) is an ideal length not only to work around, but also to construct from 2.4m (8’) standard-length pieces of timber or railway sleepers, if using these materials.
Are Shorter Length Garden Beds Better?
The benefit of breaking up a long continuous 1.2m (4’) wide bed into shorter sections is that it increases the amount of “edge” available. To understand this better, we need to introduce the permaculture design principle of the “edge effect”.
This edge effect is an ecological concept, which states where two different environments meet, there is an “edge” or interface between two different area, that creates a broader range of favourable environmental conditions or ecological niches which are able to support an increased variety of plants and animals, and are therefore more highly productive areas.
For example, a 1m x 10m bed has (2×10) + (2×1) = 22m of edge.
If we now divide the same bed into 5 sections, we now have 5 x (2×2) + (2×1) = 30m of edge.
Through this simple change we now gain an additional 8m of edge.
There is a trade-off though when using shorter length garden beds. The additional edge requires additional materials, which increase cost, but the benefit of increasing edge will outweigh the initial outlay in materials.
The other consideration is space, the shorter beds require more space because of the spaces between them.
When using harder wood, it may be necessary to pre-drill the holes with a drill bit which is narrower with the screw, then screw into the holes.
When using very thick pieces of wood, it may not be possible to get screws long enough, and it may be necessary to use long coach screws with a hexagonal head (like a bolt) that are tightened with a spanner or socket set.
What Are the Benefits of Using Raised Garden Beds?
There are many benefits to using raised beds, and these include:
- increased productivity
- better soil conditions
- increased usage flexibility
- more efficient irrigation
We’ll examine each of these benefits in the following sections.
1. Raised Garden Beds Increase Productivity
The most important benefit of raised garden beds is increased productivity. Raised garden beds are at least twice as productive as a conventional garden.
Raised beds are more productive per square foot, because plants can be spaced more closely together. This is because you don’t need to leave spaces to walk through, because you don’t need to ever step on the garden bed, ever.
Having a higher density planting also has the advantage that plants growing there will shade out bare soil, making it harder for weeds to grow there.
According to Ohio State University:
“In a traditional home garden, good management may yield about .6 pounds of vegetables per square foot. Records of production over three years in a raised bed at Dawes Arboretum near Newark, Ohio, indicate an average of 1.24 pounds per square foot, more than double the conventional yield.”
2. Raised Garden Beds Provide Better Soil Conditions
Since there is no soil compaction in raised garden beds, there is no need to plow, till, fork or dig the soil to loosen it up, traditional practices which destroy the soil structure and do more harm than good. For this reason, raised bed designs also lend themselves very well to the gardening technique of no-dig gardening.
Raised garden beds can be used to overcome issues of poor drainage, poor soil, or even no soil, such as gardening on top of concrete or asphalt, because we construct or purchase the garden bed, fill it with the type of soil we require, and build the soil further it by adding organic matter. It’s possible to create a number of garden beds with different soil blends in each for a variety of different growing environments.
By not stepping on the soil, we avoid soil compaction. When soil is compacted, water and air do not move as easily through the soil to the roots of plants. Plant roots have trouble growing through compacted soil, limiting the plant’s access to water and nutrients. It has been suggested that soil compaction can lead to a 50% loss in productivity.
3. Raised Garden Beds Provide Flexible Growing Options
Raised Garden beds offer a wide range of growing options. It’s much easier to attach trellises, supports, frames, fences or shade cloth over or around the bed temporarily, or permanently as part of the structure.
For people with physical limitations, such as those unable to bend over, or who are confined to a wheelchair, waist-high raised garden beds are the answer. A bed of this height will enable the person to partake in their interest in gardening without hindrance.
Also, by not having to step into the garden bed, it’s possible to tend to the garden all year round. Gardeners can sow, plant and harvest, whenever they want, even when the ground is wet, because they won’t be stepping in mud!
4. Raised Garden Beds Can Be Irrigated More Efficiently
With their raised sides, raised garden beds can support very thick layers of mulch over the soil, which will not slide off, or be blown or washed away.
This aids in water conservation, and also makes it easier to enrich and build the soil through the constant addition of organic matter.
The dimensions of raised garden beds also lend themselves to the installation of drip irrigation, which is an efficient way to water the garden, minimising loss by evaporation, and reducing disease by not wetting the plant’s leaves.
Another way to form a raised bed is by using old steel roofing sheets cut in half lengthways. The sharp edge is then folded over with a pair of pliers and these sheets are supported with steel rods on the outside. Once the compost , soil etc are on the inside, the sides stand solidly upright. It works really well but is not as aesthetically pleasing I grant you but a lot cheaper, if cost is an important factor.
Another good read, thank you for all the hard work!
Cheers Jan
Thanks Jan, that’s a great idea!
Creosote, diesel, tar and a bunch of other toxic gear is found in old railway sleepers (as is noted in the article above) yet your garden beds featured seem to be constructed from this product (at least, that’s what the pic says). While those beds seem to be ornamental rather than edible, is there not ongoing soil health issues associated with the use of this type of product in gardens?
Hi Rufus,
Toxic products in the garden, heavens no! Definitely not here. This an organic garden, the raised beds are constructed of NEW redgum sleepers, totally untreated, and not cheap either..
Thanks, I am happy to hear you say that the beds appear to be ornamental, actually, that suggests the garden must look aesthetically pleasing, I consider that a compliment. Yes, my garden does not have neat little rows of identical vegies in traditional monoculture style, which is just a pest insect banquet arrangement in real terms. In actual fact, it’s all edible, the rest is herbs and companion plants, there are a few ornamentals, but not in any significant numbers! This is what an overstacked, companion planted, food garden actually looks like. This is how nature grows plants, that’s how we do it in Permaculture. The farms have got it seriously wrong. If you want to know what’s in the beds, take a look at my initial design and the plant list I posted recently.
As you rightly point out, there are issues with using treated timber in a food garden, or nay garden for that matter, the toxic timber treatments do affect soil health and do accumulate in the food grown in such soil, something best avoided! Best advice is to keep it natural!
Regards
“Yes, untreated timber will eventually rot and break down, and thats what nature intends it to do, so if you want to use timber raised beds and wish to garden organically, its best to come to terms with this idea”
not best to do this. rebuilding fences, beds & compost heaps is extremely impractical (wasteful in new wood & labor)
a better alternative must be out there. hemp boards might be it
Hi David,
Hemp boards are a great idea! They are a renewable resource and sound very promising. Not sure of their suitability for outdoor structures, I honestly dont know enough to comment about this application, but their suitability in the indoor applications is beyond question. They make an impressive composite wood, and when made with non toxic glues, can be used to replace chipboard, MDF and other wood composites, all of which use toxic formaldehyde based glues which out-gas toxic volatile compounds into the home. Hemp boards are stronger than these composites because hemp fibres are extremely long, much longer than short wood fibres. Hemp is also resistant to fire, fungus, rodents, and insects including termites. Thanks for raising awareness for such a fantastic material!
I got a bit excited there, and went off the topic! Back to raised beds, here are a few thought.
The nature of all things is that they are ultimately impermanent. Our modern society seems to think otherwise. Even treated timbers eventually break down and dump their toxic payload into the soil.
Remember, when we practise soil building, we are building a vibrant living ecosystem, we encourage the organisms that break down and decompose both green and woody plant material, in order to create a nutrient rich humus filled with life. The organisms that make this possible, the fungi, bacteria, insects and other myriad lifeforms will not discriminate between dead timber. Most timber treatments work by killing these very same organisms. So you can imagine what they do to the soil.
Also, because a rich, living humus retains moisture well, things break down faster. The ends of my tomato stakes sometime rot off and get taken back up into the soil as quickly as a season or two. This is what a healthy soil is expected to do and a sign that the soil is healthy. (Note that I don’t water very often either!)
We can make wise choices to use the most sustainable materials available, ones with low embedded energy, and so forth. Ultimately its a trade-off or compromise of some sort. Recycled bricks make for an Earth-friendly solution, besser blocks or concrete will last for ages but are expensive, have high embedded energy, and concrete leaches lime into soil which some plants dislike. I prefer to use natural materials for a more natural feel, knowing the nature of such materials.
There are many choices we have in how we build raised beds. Ultimately, its about making responsible decisions for what materials we choose to use.
Regards
Another way to create raised garden beds cheaply – and minimum effort – is what my elderly (aged 88) uncle uses. Chicken wire formed into rounds (about a metre diameter), joined by twisting wires, and lined with black plastic, folded slightly over at the top. He then fills the interior with soil and compost which holds it all in place. If necessary he clips the plastic to the wire with pegs. He has several of these in the small backyard of the unit where he lives – and grows much of his own vegetables. Another advantage is that he doesn’t need to bend to tend his crops.
Steel brackets are a good way to join the sides together. But if they are not covered by soil, I find them to be not very easy on the eye
Its really a nice and helpful piece of information. I am satisfied that you shared this helpful information with us. Please stay us informed like this. Thank you for sharing.
This is a very good article on raised beds.
Another way to construct a raised bed is to use precast concrete boards (not Hardy Board) and mount them to pipes driven into the ground. The boards can be attached to the pipes with bolts that screw into concealed threaded inserts cast into the boards.
The pipes can be used as inserts for poles or frames to tie tomatoes to or to provide a support for running plants.
If anyone is interested, I will send pictures.
I would love to see pictures of your precast concrete board beds. I’ve never even heard of this material!
The concrete boards are a semi-permanent alternative that will provide a lifetime of gardening. These beds only need to built once. I have approximately $10 in each 4′ length of 12″ wide board. This includes the mounting hardware.
I would be interested in knowing more about the concrete boards. I need to start building some raised beds, to move forward with what I hope to be an urban homestead.
I used T nuts as the threaded inserts. I used 12″ masonry joint reinforcement at the midpoint of the 1.5″ thickness to strengthen the board.
I used a piece of roofing as the bottom of my form. This added some detail to the exposed face. The smoother the form is made the slicker the concrete will be. The steel roofing leaves a very smooth exposed surface.
It takes approximately 0.5 cubic feet of concrete mix for each 12″x4’x1.5″ board. The board weighs about 80 lbs. I did not see this weight as a problem, since they are not moved very often.
Excellent detailed instructions and tips on raised beds. We use the same in our garden and couldn’t be happier.
I have recently constructed raised beds using concrete Besser blocks. After a lot of consideration, I decided they were the best option for me for the following reasons:
– Concrete lasts forever
– Concrete is inert, no risk of any chemicals leeching into the soil
– Beds are easy to construct in that no building/joining is required
– Can be moved or rearranged if needed
– Holes in the blocks can be filled with soil and small plants put in, such as herbs and beneficial-insect attracting plants
– You can get them in coloured concrete, similar to the colours that concrete pavers come in, although these can be difficult to source.
Oh and I meant to say, I am so glad I just discovered your blog, it is fantastic!
Good article. Your raised bed garden is beautiful! Just a note that the “benefits” of raised beds here have nothing intrinsic to raised beds. In fact, all of these benefits can be translated into well-designed “in ground” beds. Gardeners who do so also make gardens that are less resource-intensive, more sustainable and require less work than similar raised beds. I stopped using raised beds when I discovered that they required far more irrigation and fertilization than “in ground” beds with clever “in ground” water storage. Of course, one exception is Hugelkulture beds… mine seem to require little to no irrigation at all.
Raised beds do dry faster than the surrounding ground. This can be a benefit if there are long rainy spells. I have had plants to “drown” and plants are more prone to disease if they stay wet for extended periods of time.
Youre so cool! I dont suppose Ive learn anything like this before.
So good to find someone with some unique ideas on this subject.
realy thank you for starting this up. this
web site is one thing that’s needed on the net, somebody with a bit of originality. useful job for bringing one thing new to the web!
I am wondering about creating a pentagon or greater with fruit trees to train them and tie them together over a forum(?) as here in the high desert in Colorado it is tough to grow things out of the ground out of the wind or to get the fruit trees not to freeze in a late freeze.
I love the veggie box ideas and plan to look at sizes of covering for moisture and such ideas? We get the 4 ft. concept but to extend the season up here may need to look at cover options for some of it fall.
Thanks
Gena & Todd’s
I can’t say I fully understand what you mean by a ‘forum’to grow trees over, I’m guessing you want to plant trees in a circle and tie them together over an arbor or support of some sort…
With the raised beds, you can easily construct covers for them. Some gardeners put metal pipes or short metal stakes into the soil inside the beds, and attach plastic pvc pipes/conduit to these supports and bend them into curved supports, over which they stretch greenhouse plastic or bird netting, depending on what they need the covering for.
I live in Australia and found raised beds to cook in the summer heat. The wood on the sides heats up and the first foot of soil against it becomes too hot to even touch. As a result the water loss is extreme. For me I have found heavily mulched ground level beds to work best.
Hi Jason, wood is a thermal insulator, the wood shouldn’t heat up and heat the soil.
Soil should always have something covering it, wherever it is, raised beds or in the ground – in the heat of the summer the soil should be covered with a heavy mulch or with groundcover plants.
Raised beds have better drainage than the soil in the ground on account that they are raised. If the soil in a raised bed is not retaining moisture, add compost, this will help hold moisture in the soil. When using compost as a soil amendment, use one-third compost to two-thirds soil, this is the optimum amount to add, don’t add any more than this.
A great idea for hot, dry areas are sunken beds instead of raised beds- if you have okay drainage.
I’m currently building a mandala on a field next to my house. One thing I have a lot of are rocks, so I’m using them to create my keyhole paths into the circular beds. I was thinking of putting rocks on the perimeter of the beds to separate them from the main paths between the beds, but I’m just not sure- that’s how I ended up finding your site. I have an abundance of wood chips that will go in the paths, so they’ll go down- I’m just not sure how to separate them from the soil. Unfortunately, I didn’t allow for large rock size on the perimeter, so if I use them I’ll be taking away from either my paths or beds. I won’t be buying anything, that’s for sure. I tend to use what I have first.
Glad I found your site 🙂
Hi Tessa,
Good point, in arid (desert) areas, instead of being raised. garden beds can be sunken to lower the garden to where water is more easily accessible by plant roots, and more likely to retain water when it rains.
You can use rocks for your garden border in a mandala design, but if the rock are way too big then you can use a few of them around each circular bed to define the shape, like the hour markings on a clock. If the rocks can be broken, you can smash then and use the pieces around the beds.
One technique for wood chip paths is to dig out the paths and put the excess soil into the garden beds, then fill the trenches you have created with wood chips till they are level with the soil or a bit higher. As you walk on the paths the wood chips will compact and your paths will become level with the garden bed soil and wont spill over. The great thing with this method is that the wood chips eventually break down and create nutrient rich soil, so you can keep adding fresh wood chips and the earthworms will carry the nutrient rich material at the bottom that is well composted into the adjacent garden beds.
Thanks, Angelo. Maybe I’ll break the rocks to get the size I need- great idea! All true about the wood chips- early in the year I spread them everywhere, even on my beds as a mulch. Now I have worms everywhere, and mushrooms too, which is a great sign the chips are doing exactly as hoped. There was some nitro loss initially- I wish I would have had some blood meal, but I wasn’t growing much this year anyway. This was a soil building year. Now if only I can find a great perennial vegetable sources for my zone 5.
Back to the mandala. The soil here is awful, so I’ll be planting cover crops, which will also help define the beds pretty quickly I guess I’m a little concerned about the ease of turning then in if rocks are there.
Thanks for the help!
There’s no need to turn the soil, you can just use a ‘no-till’ or ‘no-dig’ system, I’ve been using this approach for many years now, it’s such a relief to never have to turn soil ever again. I’ve written an article on the topic – http://deepgreenpermaculture.com/diy-instructions/no-dig-gardening/
It’s really easy to convert an existing garden bed, see the second half of the article, hope this helps!
So true about going up rather than digging down- this is how I’ve built all my new beds in the yard and have improved the existing ones too. This is how I’ve always done it. However, with the field I had huge rocks everywhere that had to be removed- after that there were giant holes everywhere. Knowing this and other things about the area I did some research and many permaculturists do till in certain situations- this field met that and so after getting the many and huge rocks out i tilled shallowly. To break up and level the soil before adding new. Next I’ll sow cover crops.
I was referring to the cover crops being turned into the soil in the top few inches when I said turning- so you don’t turn them in you just build layer up from that? After they start growing well, and before they set seed, I considered just adding straw to the top, then going from there with more layers. I’ve added turnips to the mix for my cover crops so I’m not sure I’ll do that.
Thanks so much for your input!
Thanks for the clarification. Both with ‘green manures/living mulches’ which are chopped down to add organic matter, and with all my regular annual vegetables at the end of their season, I practice a technique called “chop & drop” – after the plants have been harvested, I chop them at the soil level, leaving the roots in the soil, and drop the above ground growth on the soil surface as mulch. I’ll chop the tops up into small pieces most times, either there and then with my secateurs by hand, or I’ll feed them through my electric mulcher.
This system is a form of sheet composting, and the earthworms will dig down the composted material through the soil on their own, saves me digging it in! The roots rot down to create an incredibly intricate network of air channels which naturally aerate and decompact the soil, and allow water to infiltrate deep into the soil, which is why I don’t disturb the soil. Also, all the soil fungi (which are highly beneficial to plants) live mainly in the top 15cm (6″) of the soil, and get severely disrupted if you dig them up. This technique works for all plants except the brassicas (cabbage, cauliflower & broccoli family), because if you leave their roots in the soil, they produce plant growth inhibitors as they rot down – pull them up and compost them.
Hi,
I’m currently researching how best to approach some raised garden beds for food growing (the usual herbs and veggies). I’m weighing up going with untreated hardwood or the corrugated iron bed kits that are available. Would be interested to hear your thoughts re the metal kits – I would have thought they would be designed to avoid health risks? But to be fair, I don’t know enough to be sure at all!
Thanks in advance – what a great blog 🙂
Where did you buy the spiked extension metal brackets? Been looking for something like that but can only find corner. Thanks!
They’re quite easy to find here at landscaping supply outlets.
Very informative post! I know this is an old thread, but I’m also looking for brackets like the ones you mention (spiked extension metal brackets) and I can’t seem to find them. Do you have a brand name? Thank you!
I get mine from a local landscaping supplies store, so if you check with any landscape supply stores they might have something similar for the purpose of securing railway sleeper garden edging.
Can anyone recommend a material to use to divide up a raised bed, to allow crop rotation? Fibrous cement sheeting?
There are a lot of materials you can use to divide a garden – timber or plastic garden edging, stones, bricks, or even paths. The paths can be dug out and filled with mulch, which will slowly break down and add organic matter to the soil.
Thanks Angelo. It’s one big rectangular bed built with wooden edging, raised about 1m. Some of those options could work.
Great article
Great Article
When using sleepers do you suggest concrete in the posts?
I use wooden posts because its very difficult to fasten the sleepers to the concrete. Wood can be screwed or bolted together.
Sorry I should have worded my question better
I am going to place sleepers down with posts coach bolted to the sleepers, should I concrete the post into the ground
Don’t concrete them in, the raised beds definitely don’t move wherever you place them, and the advantage of not concreting the posts into the ground is that you can assemble them on a flat area of ground somewhere else and move them into place with a few people helping.
Putting the short length internally so that it is 4 foot wide internal width gives more growing space.
1200 internal width, 2150 internal length is 2.58 square metres
950 internal width, 2400 internal length is 2.28 square metres
So better to do the full 4 foot internal width as long as you have reasonable reach.
I find your website very helpful. I would like to build a raised bed garden approx. waist high for less bending, but I am wondering how one would apply the guilding principle in such a situation. Would planting a tree (trees) outside the raised bed be appropriate?
Thanks…..
Waist-high raised beds still need to be built at the optimum width for ergonomic access, it’s the same standing and bending over at waist height, no difference.
You would definitely plant trees straight into the ground, there is no benefit in putting a tree in a raised bed as it limits the spread of its roots and raises the canopy beyond reach. The only viable reason would be to elevate it for better drainage but then you would really just mound the soil and plant into that instead.
Hey there, great work but I have some food for thought…you have a no dig policy but from where and how does all that topsoil fill those beds?
Simple, the no-dig materials break down to create the topsoil, just like in Nature! 🙂
So if I understand you right, the soil content of your beds comes entirely from onsite mulch/compost etc?
If you mean no-dig gardens in general, if they are not built on top of existing soil, then yes, all the material is brought in to build the beds as described in the articles.
If you’re referring to my own garden, the no-dig beds are built on top of existing soil, and all green waste goes into the beds as a form of ‘sheet composing’ directly, or it goes into compost bins for and then it goes into the garden. Kitchen waste and food scraps go into either the worm farms or bokashi bins for processing then go into the garden.
After trial and error I have changed the concrete beds to eliminate all hardware. I cast 1.5″x4’x18″ concrete boards. I dig a trench 6″ deep and set the boards on edge and backfill the trench. doing this anchors the boards and prevents grass from growing under the bottom edge.
I have approximately $6 in each piece. A 4’x12′ bed cost $32 to construct.
I cannot figure out how high the bed should be in the end. All layers add up to over 30 cm, but your railroad wood is only 20 cm. Can you clear this up, please?
Birgit
The bed can be as high as you like. Which layers are you referring to, the ones in the No-dig Garden Bed article? In the section “Converting Existing Gardens to No-Dig Gardens” I only have two layers and they all add up to 15cm.
Angelo,
I was referring to the height of a note to garden on top of concrete.
Birgit
If the raised bed is built on top of concrete it will need to be at least 40cm (16″) deep to grow annual vegetables, and preferably deeper.
I use 20cm deep raised beds to separate the garden from the paths and to hold the materials in place for the no-dig garden beds.
What about curved or circular beds.
They can be made out of corrugated iron curved around posts, pavers, bricks & mortar, concrete block, landscaping blocks specially designed for constructing curved beds, rendered earth bags, the choices are endless.
I have read conflicting information about using treated sleepers in creating raised beds. Unfortunately I have just constructed mine from this material and am now concerned for our health. Can you please refer any scientific references that actually document how these specific toxins (eg. arsenic) are taken up by the plants from the sleepers? And of course, how the plants actually retain these chemicals through their life cycle, since it is implied we will be consuming these toxins.
Thank you, much appreciated!
Hi Martha, are you in Australia? The use of Copper Chrome Arsenic (CCA) treated timber for non-industrial (domestic) use has been banned in the US and Canada for the last decade, it’s similar in Europe. Meanwhile, Australia, being the backward country that it is (where I live!), is only concerned with protecting corporate interests and not following their lead, is holding the position that the US EPA initially and mistakenly held in the 1980s and 1990s which they have long since revised. New Zealand, being equally pathetic, has chosen to follow Australia’s backward stance unfortunately. It looks like objective scientific evidence that drove a regulatory change in the Europe, US and Canada doesn’t cut it for countries Australia and NZ for some reason…
From the US EPA website (http://www.epa.gov/oppad001/reregistration/cca/):
“Arsenic and potential risks to human health
Arsenic is a known human carcinogen and is acutely toxic at certain levels. When estimating the potential risks that a chemical may pose, one must consider two factors: toxicity and exposure.
Toxicity is described as the harmful effects that the chemical may cause, which is often dependent on the amount or dose received.
Exposure is the dose received, typically orally or through contact with the skin, or by inhaling, over a certain period of time.
Thus, whether any risk exists is dependent on both toxicity and exposure. Arsenic is a naturally occurring chemical that can also occur in drinking water, food crops, and soil.
Leaching of arsenic from treated wood products into soil: Published results of scientific studies suggest that arsenic slowly leaches from CCA-treated wood products. The amount and rate at which arsenic leaches, however, varies considerably depending on numerous factors, such as local climate, acidity of rain and soil, and how much CCA was applied.”
From another US EPA document (http://yosemite.epa.gov/opa/admpress.nsf/b1ab9f485b098972852562e7004dc686/1a8cfb4970823b3885256b5e006ffd67?OpenDocument)
“Arsenic is a known human carcinogen and, thus, the Agency believes that any reduction in the levels of potential exposure to arsenic is desirable. As always, when children play outside, whether around CCA-treated play structures or not, they should wash their hands prior to eating. Also, food should not be placed directly on any outside surface, including treated wood. CCA-treated wood should never be burned, as toxic chemicals may be released as part of the smoke and ashes. Consumers who work with CCA-treated wood are encouraged to use common sense in order to reduce any potential exposure to chemicals in the wood. Specific actions include sawing, sanding and machining CCA-treated wood outdoors, and wearing a dust mask, goggles and gloves when performing this type of activity. Clean up all sawdust, scraps and other construction debris thoroughly and dispose of it in the trash (i.e., municipal solid waste). Do not compost or mulch sawdust or remnants from CCA-treated wood. Those working with the wood should wash all exposed areas of their bodies thoroughly with soap and water before eating, drinking or using tobacco products. Work clothes should be washed separately from other household clothing before wearing them again.”
There’s no two ways about it, it is poisonous stuff, and if there wasn’t a possible risk or danger, EPA would not have banned CCA.
From an Australian government website (http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Copper_chrome_arsenic_(CCA)_treated_timber):
“Copper chrome arsenate (CCA) treated timber is wood that has been preserved with a combination of copper, chromium and arsenic. It is important to limit exposure to the chemicals that CCA timber contains. CCA treated timber is not permitted to be used in the construction of new garden furniture, picnic tables, exterior seating, children’s play equipment, patios, domestic decking and handrails.
International concerns about CCA-treated timber
Although the chemicals are fixed within the dry wood in CCA-treated timber, concerns have been expressed internationally about the potential for harm as small amounts of arsenic can leach out of the surface of the timber.
The US and Canada jointly decided to restrict the use of CCA-treated timber in non-industrial settings after January 2004. In March 2005, the Australian Pesticides and Veterinary Medicines Authority (APVMA) reviewed the safety of CCA-treated timber use in Australia.
Australian recommendations
CCA-treated timber should not be used to build childrens play equipment, patios, domestic decking, handrails, new garden furniture, exterior seating or picnic tables.
CCA-treated timber can be used for poles, fencing, landscaping timbers, piling and other structure foundations, residential construction, industrial and commercial construction, rural and farm use, fresh and salt water structures, signage and boat construction.
Existing structures made from CCA-treated timbers do not need to be removed and replaced until they reach the end of their functional life.”
From the Canadian government website (http://www.hc-sc.gc.ca/cps-spc/pubs/pest/_fact-fiche/cca-acc/index-eng.php)
“Is there a risk that the CCA preservative can leak out of treated wood?
It is possible that some of the preservative will be dislodged, depending on various factors such as wood species, treatment practices, age in service, and the environment in which the treated wood is installed. It is known that treated wood continually exposed to water in damp soil will lose more preservative than that exposed to an occasional rainfall. These factors are currently being re-assessed as part of the re-evaluation of CCA.
Is it safe to continue to use CCA wood preservatives when a risk of exposure to arsenic and these other metals exists, especially when it comes to children’s exposure?
Arsenic, chromium and copper occur naturally in the environment.
Some studies have found that small amounts of arsenic, chromium and copper can dislodge from CCA-treated wood used in playground structures.
When the U.S. EPA reviewed CCA wood preservatives during the 1980s it concluded that CCA-treated wood did not pose an unreasonable health risk. A similar assessment, conducted by the U.S. Consumer Product Safety Commission in1990 concluded that short- and long-term health effects are unlikely to occur for individuals coming into contact with treated wood. Health Canada critically reviewed these assessments and agreed with the overall conclusions at the time.
The re-evaluation of CCA is examining whether the exposure to these metals as a result of contact with CCA-treated wood and soil containing leachate from CCA-treated wood presents an unacceptable health risk to the general population and sensitive sub-groups such as children. Previous assessments, and possible mitigation measures, are being considered during the current re-evaluation.”
Despite some questionable opinions which aim to downplay the risk, the fact is that arsenic and chromium are toxic, and copper in high concentrations is toxic to plants, everything breaks down in time, even treated wood, which can contain up to 10% by weight of CCA, which of course will end up in the soil eventually, resulting in toxic soil contamination.
Plant do take up what’s in the soil, and certain plants can accumulate certain minerals at higher concentrations than the soil, hence the caution about growing root crops in lead contaminated soil (resulting from the stupidity of adding tetraethyl lead to petrol (gasoline for you Americans!) as an anti-knocking agent in previous decades and contaminating all the soil around roadways, with toxic lead, as well as the equally idiotic idea of using lead as a paint pigment, which contaminated the soil in the garden beds around homes).
There are alternative treated timbers which are safe, those treated with CQA (copper quaternary ammonium) sold as “Eco wood” are suitable for this task.
I do live in Australia (I have CCA wood) and now I’m faced with the decision of using this raised bed to grow vegetables or not. I am considering lining it with plastic in hopes that a physical barrier would reduce leaching into the vegetables? This seems logical to me, surely there would be significantly reduced contamination if there is a physical barrier. Otherwise I would not know what to do with this “toxic” wood. I am so disappointed as I was really hoping to grow some food in it. Thank you for sharing the info.
This is an extremely helpful article on raised bed! Thank you my friend =)
-Alison
Hi Angelo,
Great page and great site! Thanks also for that important info on CCA treated materials.
I’m in the process of building some raised beds out of cypress.
My question, however, is about levelling the beds. Given the permaculture principles regarding the use of slope, should I be aiming for the beds to sit on the un-levelled earth, or should I excavate to get them level? The gradient I’m working with is actually pretty slight, but I thought I’d asked for a perspective.
Cheers, David
Hi David, it’s very easy to level a raised bed, to raise any side to level the bed up, you just push some soil under one side to elevate it and compact it down a bit so it stays put. If the soil doesn’t stay, a large stone or a bit of wood can prop the compacted soil up until you fill the raised bed with soil, then it then it will stay in place levelled.
Raised beds water more uniformly if they are level.
There are some new timber treatments where they blast the timber with copper nanoparticles. I read they are meant to be the safest treatment, but some people have expressed concern over the use of nanoparticles. I have built beds from cca sleepers but have lined them with plastic as they were wicking type beds. It certainly isn’t my first choice but acq treated sleepers are almost impossible to source in Townsville where I’m based. I generally use 25mm thick acq treated plantation pine planks, which I have to purchase in 160 length lots (150x25mm x 2.4m) as only cca treated plank are available locally and they have to be ordered in. Three planks high gives a bed height of 450mm for herbs and veggies and four planks high is 600mm which is deep enough for bananas and fruit trees. As I live in the dry tropics I line the bottom section of the beds with plastic and plumb them with socked dotted drainage pipe, with the drain 150mm off the ground. I fill with soil and have no gravel or sand layer like conventional wicking beds. To stop the saturated anaerobic soil at the base of the bed from going ‘off’ and creating methane I use an organic probiotic fertiliser made from food waste fermented with a modified EM (Effective Microorganisms) brew that replaces the methanogenensis microbiome with beneficial anaerobic bacteria, including purple non-sulphuric photosynthetic bacteria that utilises infrared light to sequester both nitrogen and carbon in the soil. The nitrogen is converted by other bacteria to become fertiliser for plants and the carbon improves soil structure. In this way these permaculture-designed BioWicked beds turn a problem into a high nutrient solution 🙂 As a side benefit the foof-waste-food cycle is carbon negative as more carbon is locked up in the beds than is released in the food waste fermentation.
Incredibly helpful. I’m in NM, USA and have horrible granitic soil, takes an hour to dig 6inch hole for planting, in our foothill location. Going raised for veggies, and in ground for natives. Debating getting galvanized water troughs, drill holes for drainage, fill with soil compost mix. My debate is if the metal will cook, and if I would be better off with cinder blocks. High desert leads to large diurnal temp swings and very little rain (less than 10 inches per year). Thoughts? Thanks!!!!
You can make removable decorative timber panels to cover the sides of the steel tanks if you don’t want them to heat up too much, but the tanks should be fine on their own as long as you water the plants. In Australia galvanised or coated (Colorbond) raised garden beds are popular, and our temperatures get fairly high, in Melbourne where I’m based our summers are hot and dry and temperatures are in the mid 30s to low forties (degrees Celsius) which translates to 95-108 degrees Fahrenheit, though we get 60cm (24″) of rain a year in our part of the country, but we still need to supply water to our gardens.
Hi there, I was just wondering, going with the ergonomic thought process, what width you would suggest between beds in order to be able to weed/harvest/walk and enjoy whats growing! Thanks for the great info :o)
Minimum path width is 45cm (18″), maximum width I would use is wide enough to fit a wheelbarrow if I was using a wheelbarrow to carry bulk materials around the garden.
Now, if you have many people working on a garden bed all at once, such as in a community garden, then you need to allow space for two people to comfortably pass each other.
Loved your article. Many thanks for the advice.
To all who have or will be using cinder blocks or forms of concrete, please do some research as both may have “fly ash” in them. Fly ash has toxic properties.
Jamie with Bees in San Francisco
Hi Angelo,
I’m currently designing by backyard food forest In Geelong and want to incorporate no-dig raised beds on top of my soil with Backyard Orchard Culture. I am designing my guilds with my fruit trees as the top layer in these beds, however I was a bit concerned about you mentioning to plant fruit trees in the ground instead. It looks like in your design you planted your fruit trees in beds – how did you manage to incorporate these two techniques (no dig and b’yard orch culture)?
Thanks,
Chris
Hi Chris, the raised beds in my backyard food forest are a single 20cm high sleeper, they’re used more as edging to separate the paths from the no-dig garden beds that are built on top of the soil. They hold in the mulch and other materials in place in the no-dig system.
Small trees are often planted in raised garden beds or large planters filled with soil. They can be converted to no-dig beds, that will work fine.
I caution against planting trees in garden beds that filled only with no-dig materials because the soil level will drop when they’re first built and the materials begin breaking down, which isn’t a concern for annual vegetables.
I am not using three of my beds this year they are 4 x 8 and 4 foot high. I have turned over my ground cover and put Compost on top and Im wondering if I should put a tarp or something on top of that for the summer?
Thank you Mo
You’d be better off planting a warm season green manure, you can get green manure seed mixes for warm and cool season, just sow the seeds, let the plants grow, then cut and dig the plants into the soil to rejuvenate it and replenish the nutrients.
I’d like to make a comment about reusing old corrugated iron roofing for raised garden beds. Please be careful, the old corrugation may have used lead in its galvanising.
Also, people tended to paint on galvanised roofing; because of its age, it’s very probable that the paint may also have contained lead.
I used to work for a major Sydney utility and lead leaching from peeling lead paint into the soil was a big problem. There was an instance where adjoining people kept chickens and grew vegies. The soil was tested and found to be contaminated. Then the people got tested and were found to have very elevated levels of lead in their system. The people had to be moved and all the contaminated soil (sampling from test pits showed the areas with various measurements) removed and certified ‘virgin excavated natural material’ brought in.
Working for the this major utility made me more conscious of contamination considerations.
Thanks for your comment. The galvanising process only uses zinc, so there should not be any concerns with lead contamination. I’ll research the topic in case there is lead impurities in the zinc galvanising and write an article on it.
Peeling lead paint is definitely a cause of lead contamination of the soil, and building raised beds above lead contaminated soil, with a layer of root barrier plastic underneath is a great way of using these spaces to grow food. Lead test kits are cheap, I’ve purchased mine online, best to test any painted corrugated iron before putting painted surfaces inside the bed where soil is in contact with it.
I live in Missouri and have access to cedar at a very reasonable price. I char the boards with a brush burner before assembling the raised bed. Our local farmers have charred their wood fence posts before building for over a century. The Japanese have used this method on exterior siding for thousands of years. I believe they call the technique shou sugi ban. They do oil the wood after burning it. Charring the wood makes it rot resistant, insect resistant, and fits in the permaculture structure as I see it.
Thanks Craig, that’s an excellent idea and a very sustainable way of preserving the timber. It fits the permaculture approach very well, appreciate you sharing this here!
i’m about to make three raised garden beds replacing my current beds, in a U shape. these are under the hills hoist over which i grow passionfruit vines for shade in summer. works extremely well and there is a small concrete path to the base of the hoist. three garden beds surround this. the back stairs and the hose are nearby and the aspect is north east.
am just mulling about whether to use besser blocks or timber. thanks for your comments everyone.
Hello, I read your article on raised garden beds with great interest, in particular the warning on treated wood. A couple of months ago we installed a couple of EcoWood raised beds, which I note are treated with copper azole (which is marketed under the Tanalith brand). We are using the beds to grow vegetables and herbs. I had no idea when I purchased these that this treatment could be toxic. What would be your recommendation Angelo? Should we decommission these beds? Thanks so much – loved your companion planting session on Zoom recently!
I had a look at the cocktail of chemicals, including toxic fungicides in Tanalith, and their toxicity, it would take me a whole article to spell it all out and explain the science, which I don’t have time to do right now. The Ecowood treated with CQA (Copper Quaternary Ammonium) seems a lot safer. I personally wouldn’t use any treated wood around a vegetable garden, some people might be inclined to line the beds with plastic to minimise contamination, it’s a personal call really. Glad you liked the companion planting class online, thanks!
Hello – what advice might you give to filling new raised beds to ensure the healthiest soil thank you
You can either use the no-dig gardening method to make new soil from scratch, or you can fill it with a premium garden soil blend from a garden centre or landscape supply yard. I use a combination of 50% premium garden soil, 25% organic compost to improve soil structure, 25% organic cow manure for increased soil fertility.
Any thoughts on the use of fly ash in old bricks (or in their mortar) and its potentially toxic effect on soil that would come into contact with it?
Thanks for this excellent post.