- Wicking Bed Construction
- The Advantages and Disadvantages of Growing in Wicking Beds
- Wicking Bed Design Theory
- Wicking Bed Materials
- Wicking Bed Construction – Step by Step
- Getting More Out of Your Wicking Bed
- Wicking Bed Maintenance
- Building Wicking Beds in Melbourne
- So, What the Heck are Wicking Beds?
- Pros and Cons
- They just work!
- Getting a Wicking Bed
- Building a Wicking Bed
- Wicking Beds and Raised Garden Beds are an Essential Component of Urban Gardens
- How Are Wicking Beds Different Than Garden Beds?
- Where Is The Best Place To Put A Raised Garden Bed?
- How to Build a Wicking Bed
Wicking Bed Construction
A wicking bed is a self-watering raised garden bed, and even though the design is a relatively new innovation that is catching the attention of many produce gardeners worldwide, it is essentially nothing more than a large scale version of a self-watering pot. Self watering pots have been around for decades, and are based o the principle of sub-irrigation, where the water supply sits below the pot that is wicked upward into the soil in the container above.
This article provides detailed step-by-step instructions on how to build a wicking bed, but before we start building anything it is important to understand how wicking beds work, so we know exactly what we’re building and how to modify the design to our needs if we need to.
Also, when considering wicking beds, it is really important to determine whether this system of gardening is suitable for our needs as gardeners. By understanding the pros and cons of wicking bed gardening, we can make the right choice and get the best results gardening with this wicking beds.
The Advantages and Disadvantages of Growing in Wicking Beds
Wicking beds are great for situations where watering is infrequent, such as community gardens and school gardens where nobody is present over holiday periods to water the garden beds. The water reservoir in a wicking bed can carry enough water to keep the plants alive for up to several weeks depending on climate, season and location. They’re also useful for gardening under and around trees with invasive roots that extract every last bit of moisture from the soil, such as Australian eucalyptus trees.
Growing plants in wicking bed systems is a useful technique that increases the range of possibilities of what you can grow where, and wicking beds have their place and purpose in a gardeners repertoire, but they also have their limitations just like any artificial gardening system. What are these limitations you may be asking?
Most plants require a wet-dry cycle to grow, but wicking beds create an environment with constantly moist soil which is unsuitable for many plants. Since water is retained in a wicking bed, this leads to a build up of fertiliser and the evaporation of water from the soil combined with the upward wicking creates a situation where the concentration of salts can build up to dangerous levels in the soil that can burn the roots of the plants. Also, the upward moving water carries the excess salts upwards, so the salts accumulate at the upper soil levels where shallow rooted seedlings are planted.
Another issue is that the lowest soil levels in wicking beds are always wet, while the upper levels can be fairly dry, because the soil can only wick moisture up so high through the forces of capillary action, adhesion and cohesion against the forces of gravity. As a consequence, the moisture available to a plants depends on the height of the garden bed and the depth of the plant roots. Deep rooted plants which dislike ‘wet feet’ (constantly waterlogged soil) will be very unhappy in a wicking bed, and will usually fail due to root rot. It is also important to consider that a wicking bed in in fact a container garden, and all containers of soil or potting mix/medium have what is termed a ‘perched water table’, a layer of water-saturated soil at the bottom of the container that never drains away. If this layer is constantly wicking up more water, it can never dry due to evaporation or uptake by plant roots, and becomes a soggy, anaerobic (without air/oxygen) sludge that may promote root diseases.
The main drawback for most people is cost. Large properly built wicking beds are expensive to build. In my mind gardening should be simple, cheap and sustainable. My basic rule of gardening construction is as follows. Only use a raised garden bed when growing in the ground is not possible. If using a raised bed is not possible, only then use a wicking bed. The cost and construction effort involved going from gardening in the ground to raised beds to wicking beds jumps astronomically with each step.
Wicking beds are not a universal gardening solution, and if we keep this in mind and use them where they perform best, we can best make use of the benefits while avoiding the disadvantages.
Wicking beds in my opinion, much like hydroponic systems, are best suited to growing annual vegetables, which are so short lived they don’t live long enough to develop long term problems due to the soil conditions, and require large amounts of nutrients in a short period. Since wicking beds retain fertiliser all too readily, less fertiliser can be used for annual vegie growing. As such, wicking beds make great intensive vegie beds and kitchen garden beds.
Now that we understand the benefits and limitations of a wicking bed system, let’s have a look at how they work..
Wicking Bed Design Theory
A wicking bed is quite a simple design as shown in the diagram below
The size of the wicking bed is essentially personal preference, it can be vary from a small tub which sits on a table or stand, all the way through to a full garden bed sized wicking bed system.
Common wicking bed sizes are determined by the dimensions of commercially available raised beds or construction materials.
- For very large wicking beds, railway sleepers are often used, and the dimensions and efficient use of materials dictate the size. A railway sleeper is 2.4m (8’) long so a popular size is 2.4m (8’) x 1.2m (4’) as this uses three sleepers to construct a single level. A typical height when using such materials is 60cm (2’) high, as each sleeper is 20cm (5”) high, and if they are stacked three high, the total height is 3 x 20cm = 60cm (3 x 8” = 24” = 2’). Such a design uses 9 full-length railway sleepers. Another design option to save 1/3 of the materials is to dig a trench in the ground for the water reservoir level so the pond liner sits below the ground 20cm (8”) with the outlet at the same level as the ground, this way you can use only so the two levels of sleepers instead. By comparison, such a design uses only 6 full-length railway sleepers.
- Galvanised or coated steel raised garden beds of various dimensions are also commonly used as long as they are of adequate depth. Typically something around 70cm (28”) high works well as this allows for a good depth of soil, and enough of a lip above the soil level to hold mulch in place.
- If using a small container which isn’t that deep you wont be needing a 20cm (8”) deep water reservoir, you can scale it down to suit the dimensions of the container.
Wicking beds design showing the components of the system
If we look at the wicking bed design shown in the diagram, we can see it is constructed of several layers or levels. The best way to explain how the wicking bed system work is layer by layer, in the same way that it is constructed.
- The ‘shell’ of a wicking bed is a pre-constructed or pre-fabricated raised bed, it can be made of steel, wood, whatever is strong enough to hold the required amount of soil.
- The raised bed ‘shell’ is lined with pond liner so that it can hold a large volume of water. It turns the raised bed into a very large watertight container.
- A hole is drilled through the raised bed and pond liner to fit the overflow pipe (threaded tank inlet or bulkhead fitting), at a height of 20cm (8”), which allows the water to flow out when the water level gets too high.
- The pond liner water reservoir is filled with coarse scoria (a porous red volcanic rock) to the height of the overflow pipe. This layer will hold the water. the water sits in the spaces between the scoria, and wick it upwards. The scoria layer also serves as a structural support to hold up the soil above it away from the water below.
- The L=shaped inlet pipe is put into place before the scoria is laid down, it serves as a water inlet to fill the water reservoir with water. The vertical pipe is joined to the horizontal pipe with a 90-degree elbow join. The lower horizontal pipe has holes drilled right along its length so water drains out more easily.
- The scoria layer is covered with geotextile fabric or shade cloth to keep the soil layer above it from falling into the scoria layer water reservoir – essentially it is a barrier that separates the water below from the soil above.
- The soil then fills the bed to a level just below the edge of the pond liner, so the pond liber sits slightly higher than the soil level.
The wicking bed is filled with water from the inlet pipe to fill the water reservoir, when it is full, some water will flow out of the overflow outlet. The water will then wick upwards as high as it can to keep the soil damp.
By understanding how a wicking bed works, we can get a better idea about how we want to design one and determine the quantities of materials required tor construction.
Wicking Bed Materials
Wicking beds require a lot of materials to construct, and as a result, they are not cheap.
To construct a wicking bed you will need the following materials:
- Raised garden bed – prefabricated steel raised garden bed or DIY timber raised garden bed
- Pond liner – either PVC or the more expensive butyl rubber (these have very long warranties on then and are designed not to leak. While some people use black builders plastic, it is not as durable as pond liner and not recommended). You will need enough pond liner to line the sides and bottom of the raised bed. So, your width of materials will need to be (width of bed + 2x the height), and the length of pond liner will need to be (length of bed + 2x the height).
- Scoria (Coarse Grade) – this is a porous volcanic rock that fills the water reservoir, the water occupies the scoria layer and wicks upwards. You will need enough to fill the raised garden bed to a height of 20cm (8”). To work out the volume in litres,use the following formula: (length of garden bed (cm) x width of garden bed (cm) x 20cm)/1000, so for example a 2mx1m garden bed will take (200*100*20)/1000 = 400L of scoria. or 0.4 cubic metres.
- Geotextile fabric – separates the soil from the scoria-filled water reservoir. Geotextile fabric is synthetic and does not break down, which is important. Geotextile fabric is sold as fine grade weed mat which looks like see-through cloth (it does NOT look like plastic) and can come in a few colours, often grey-black or white. As it is quite thin it is a good idea to use a double layer of geotextile fabric . If geotextile fabric is unavailable, you can use shade cloth with a high shading factor as possible such as 90% shading shade cloth, as the holes are smaller. Whichever material you use, you will need enough to cover the bottom of the raised bed and extend a little up around the sides by at least 15cm (6”).
- Soil Mix – use a high grade soil with a good level of organic matter in it. Ideally, a mix of 50% premium soil, 25% organic compost and 25% organic cow manure will give your vegies a good start.
- Water Overflow Outlet Fitting – use a 20mm Threaded Tank Inlet (Bulkhead fitting) and get a drill with the appropriate drill bit or hole cutter to drill a hole to fit the fitting into the side of the raised bed.
- Water Inlet Pipes – use two pieces 50mm (2”) PVC pipe, joined by a 90-degree elbow joint. The vertical segment of pipe should extend above the soil line at a height that allows the gardener to comfortably pour water into it (not too high), but not so low that it is lost amongst the vegetation. The horizontal section should be approximately half to three quarters the length of the bed, and should be drilled all around and over its length with holes approximately 10mm-12mm (3/8”-1/2”).
- Tools required – spirit level for levelling the garden bed and scoria laver, a drill and appropriate drill bits and hole cutters as discussed above, a set of small spring or screw clamps for holding the pond liner in place while filling, and scissors to cut pond liner.
After we have gathered the required materials, we can then begin construction. Allow a few hours for construction if you have never built a wicking bed before as you’ll be learning as you go. Once you are familiar with the process and have developed and refined a system that works for you, you’ll be able to build them rather quickly. The two wicking beds in the following instructions were built at a kindergarten with a colleague (and a lot of little children with tiny plastic spades and buckets) in a little over an hour!
Wicking Bed Construction – Step by Step
In this instructional article we’ll be using a galvanised steel raised bed as the base for our wicking bed.
Also, for ease of construction, we’ll use a slightly simpler design where the water inlet tube is just a straight pipe with no bend in it, as shown in the diagram below:
- Place or construct the raised bed in the desired location, once it is filled with soil it will be immovable!
- Ensure that it is level by using a spirit level – place the spirit level crossways and lengthways and at various angles to determine if it is level.
The wicking bed needs to be level because it will hold water at a specific height, if it is angled it will drain out one side and be too dry on the higher side or not drain properly and be wetter on the lower side.
If a side of the bed is low and needs raising, lift the bed slightly and pack more soil underneath to elevate it, if it is high, dig some soil out.
If you’re wondering about the four white tubes inside the top edge of the raised bed, they are part of it, it’s purchased that way. The vertical tubes are used for attaching flexible pipe from one side of the bed to the other to make a half-circle tunnel -shaped frame to support a covering material such as bird or insect netting. shade-cloth or plastic.
- Drill hole in the side of the raised bed, 20cm (8”) above the ground
- Lay down the pond liner inside the raised garden bed and check that it fits properly.
- Install the 20mm threaded pipe outlet (bulkhead connector). Cut a hole in the pond liner just big enough to fit it through the hole, no larger, and ensure that the rubber washer of the fitting is against the pond liner to ensure a watertight seal.
- Prepare the water inlet pipes – if using the vertical modified design, drill 10mm (3/8”) holes all around the last 30cm (12”) of the 50mm (2”) wide PVC pipe, length should extend high enough above raised bed to allow efficient watering without reaching too high or pushing plants out of the way to find the watering inlet.
If using the more common design of an “L” shaped water inlet, use two lengths of pipe and an elbow join. The horizontal section should be approximately half to three quarters the length of the bed, and should be drilled all around and over its length with holes approximately 10mm-12mm (3/8”-1/2”). Join the two pipes with the elbow join, just push-fit the pieces together, a friction-fit is sufficient.
- Lay down a thin layer of coarse scoria over the pond liner. This will bed it down and put a protective layer of scoria over the pond liner so that it can’t be damaged by the PVC inlet pipe.
Important – This modified design used only one shorter piece of inlet pipe and no elbow joint for the pipe, it is ‘I” shaped and not “L” shaped as in the previous design, so the cut end of the pipe is pointing straight down onto the pond liner, make sure there is an adequate layer (5cm or 2”) of gently packed-down scoria between the end of the pipe and the pond liner to avoid puncturing it if the pipe is pushed down!
- Clamp the pond liner to the top edges of the garden bed right around using small spring or screw clamps to keep the pond liner in place while the bed is filled with materials.
- Fill the garden bed with coarse scoria to the height that is level with the overflow outlet. Make sure that the scoria layer is fairly level and even.
- Lay down geotextile fabric (or shade cloth) over the scoria layer.
- Wrap well around inlet pipe, allow the fabric to come up around the pipe to prevent any soil entering the scoria layer.
- Cover the scoria layer with two layers of geotextile fabric (or a single layer of dense shade cloth) and extend it up around the sides of the pond liner by at least 15cm (6”).
The geotextile fabric can be tucked in all around where it makes a corner with the sides to secure it in place, just push the bottom part or the vertically extending sections between the pond liner and scoria. This is to make sure that no soil can get into the scoria layer.
- Check that the scoria layer is level. If there are any high spots, pat them down. Low spots can be raised by pressing around the sides of the low area to push scoria into the area to fill it.
If the scoria is far too uneven, lift a section of the geotextile fabric, level the scoria layer, and then put the geotextile fabric back in place.
- Check once more that the scoria layer is level under the geotextile fabric.
- Begin filling the raised bed with the soil (50% soil, 25% compost, 25% cow manure mix or your own blend), ensuring that the pond liner is kept against the walls of the raised bed as you fill with soil.
The blue plastic pot at the top of the water inlet is there as a cap to prevent dirt and other objects entering the water reservoir.
- Trim off excess pond liner with scissors leaving about about 3cm (1-1/4”) of pond liner the soil line.
- Wicking bed completed and ready to plant and water!
To get the system to wick properly, you need to evenly wet all the soil first by gently watering the soil from above repeatedly until water starts running into the scoria layer.
Once the soil is evenly wet, fill the water reservoir through the inlet pipe until water begins to flow out of the overflow pipe.
Plants up the wicking bed and mulch your plants to conserve moisture, then sit back and relax!
Getting More Out of Your Wicking Bed
Mulch – The reason why there is a considerable lip or edge above the soil level , around 10cm (4”), is to allow the bed to hold a nice thick layer of mulch above the soil. Mulch keeps the moisture in the soil, prevents evaporation, and conserves water, and the purpose of building a wicking bed in the first place was to reduce watering. If you’re building your wicking bed in the warm seasons, always mulch!
Mulch with a layer of mulch around 5-7cm (2”-3”) so the water lasts longer, and your plants roots stay cool. The mulch will also break down slowly and add nutrients to the soil. For mulch material in a vegetable garden bed, you can use pea straw, lucerne, hay or sugar cane mulch.
In-soil worm farms – you can also construct worm farms directly in the wicking bed using worm tunnels (see article Build a Worm Tunnel Vermicomposting System) so that the whole wicking bed becomes a wicking worm farm, that way the earthworms generate worm castings, one of the best known fertilizers, within the garden bed itself!
Water recycling – the water that flows out of the water overflow outlet will be loaded with fertiliser so you can run that water into a bog garden, reed bed system or a garden bed in the ground for moisture loving plants (if you get enough water overflowing!)
Extra growing space – wicking beds, like other raised beds, can support frames or trellises to grow climbing plants on such as beans, peas, cucumbers, watermelon and any other edible annual climber you fancy. Keep in mind that you cant hammer stakes or poles into the wicking bed itself, that will punctuate the pond liner and destroy the watering system. The frame, trellis or support has to either be anchored into the ground or attached to a wall behind the wicking bed.
Protective covers – as with other raised beds, you can make a frame to support bird netting or insect exclusion netting to protect the plants in your wicking bed from pests. Another possibility is to use clear greenhouse plastic to make a cloche tunnel for extended season growing.
Wicking Bed Maintenance
To maintain a wicking bed, flush out the whole system at least once a year. If the wicking bed is undercover and not exposed to rain, which helps flush it out naturally, consider carrying out the task perhaps twice a year.
To clear away high levels of salts that are building up at the top layers of the soil, water from above to wash them out into the water reservoir and out of the outlet pipe.
Also, remember to go easy on the fertiliser when feeding the garden bed in spring and autumn, as fertiliser levels can accumulate in wicking beds because every bit of fertiliser that you put in stay in the system unless it is washed out.
Other than that, maintain a wicking bed just like any other raised bed.
Now that you know whether you really do need a wicking bed, how it works, and how to build one, the rest is up to you! Happy growing!
vegetable patch design Wicking Beds Wicking bed depths The accepted wisdom regarding wicking beds is that water can only be effectively drawn up from the water reservoir at the bottom of a wicking bed to a height of around 30 cm. However this only applies to the osmotic process and does not take into account the ability of roots to extract water from much greater depths. Wicking beds can in fact be made to a variety of depths depending on the size and root structures of the plants you intend to grow in them. Below is a rough guide to the different depths for different sized plants.
Shallow wicking beds with a soil depth of around 15 to 20 centimetres draw the water to the surface of the bed providing ideal conditions for growing seedlings for transplanting.
Wicking beds with a depth of around 35 to 40 centimetres depth are suitable for growing vegetables.
Deep wicking beds with a soil depth of 50 centimetres or more are ideal for containing small trees and shrubs.seedlings : 15 to 20 cm Small wicking tubs with just 15 to 20 centimetres of soil above the water reservoir are ideal for growing seedlings for transplanting. At this depth the osmotic process draws moisture right to the surface of the soil, providing ideal conditions for seeds to sprout and young seedlings to grow.
There is however not enough space for the roots structure of most mature vegetables.
vegetables : 35 to 40 cm Wicking beds or tubs with 35 to 40 centimetres of soil above the water reservoir provide a suitable height for growing vegetables. At this height the soil on the surface is fairly dry but allows all but the smallest seedlings to reach the moist area just below the surface with relative ease.
At this depth there is not only enough room for the vegetable roots to develop properly the drier soil on the surface reduces the number of weed seeds that germinate.
If you are planting vegetables seeds into wicking beds of this depth you will have to water the seeds from above until the seedlings are big enough for their roots to reach the moister soil below.
small trees & shrubs : 50 plus cm Wicking beds or tubs with a soil depth of 50 or more centimetres are ideal for growing small trees or shrubs. At this depth the surface soil is very dry, inhibiting weed growth, while the greater volume of soil provides more room for roots to grow.
Wicking tubs of this depth are ideal for growing small trees in a vegetable patch as they prevent the roots from competing directly with nearby vegetables.
Wicking beds and tubs can also be used to contain plants that send out lots of suckers. I have used wicking tubs to contain raspberry canes.
Building Wicking Beds in Melbourne
We’ve now got a whole website devoted to wicking beds. You can buy conversion kits there and see an updated version of this article. 🙂
We’ve created a sequence with all the info you need to get started building your own wicking bed – i.e., a veggie bed that waters itself from below. It’s based on our years of experience installing wicking beds in Melbourne, Australia. We sincerely hope your water wicks well and your garden grows green and lustrous. Let’s start with the basics—and wonders—of wicking beds:
On this page:
- What are Wicking Beds?
- Pros and Cons of Wicking Beds
Elsewhere, on our wickingbeds.com.au site:
- How to Make a Wicking Bed
Here’s also an intro video about what VEG Wicking Beds does:
When we first started Very Edible Gardens (VEG) back in early 2009, we had no idea what a wicking bed was. Then, after a year or so of installing raised vegetable garden beds all over Melbourne, someone whispered the words into our ears. “Wicking beds,” they said. “We want some wicking beds.”
“Wicking beds” we thought, smiling and nodding, then scratching our heads. “What on earth is a wicking bed?” So we did some research and, equal parts intrigued and skeptical, we started to experiment. Up till then, all our raised veggie beds had been either hand-watered or set up with ‘dripline’ irrigation. But now we started setting up wicking beds in old bathtubs:
…and then, using plastic liner, in our raised VEG beds which are assembled from sleepers of locally harvested golden cypress (Cupressus macrocarpa) timber:
So, What the Heck are Wicking Beds?
Invented by an Australian named Colin Austin, the idea with a wicking bed is that you prevent water from leaving the bottom of the bed with a waterproof liner or layer. This creates a water reservoir underneath the soil. Then, rather than having to irrigate by watering from above (via drip irrigation, a hose, watering can etc), the water literally wicks up into the soil from below, keeping it nice and moist.
Now, with all that water, this could easily get messy and even stinky. But, you prevent the weight of the soil from squashing all the water out – and making a muddy mess – by having the water sit within a layer of small stones, which is able to accommodate the water whilst bearing the weight of the soil (and your prize pumpkins!) without collapsing. You prevent the soil from washing down into gaps between the stones with a sheet of something that lets water wick up, but stops soil moving down.
A little helper adds stones to the wicking
bed reservoirThe wicking process in action: water moves
up the stones! Cassie from VEG explains the geotextile
fabric layer which separates the soil (coming
next) from the water reservoir
Then you have your happy soil and plants on top of this.
The last essential piece of the wicking bed puzzle is that you need an overflow point (usually a pipe) so that the soil layer doesn’t get flooded, which would kill the soil life and plants by rotting their roots. (With the VEG Wicking Bed style ones you install them before you add the soil or stones.)
Our overflow system (now industry standard)
lets you also observe water levels
and periodically drain & flush your bed
As you’ll know if you’ve researched wicking beds online, the available information is scattered about the web in dribs and drabs and often with advice that contradicts what the other site said. So, taking it all with a grain of salt, we set out to learn by doing, our initial intention to prove to ourselves that wicking beds didn’t work. We gave it a pretty good shot, and in the process we learned a lot, and refined how we go about them enormously.
We’ve condensed all this knowledge into our How to Make a Wicking Bed sequence. But before you rush out and build one, take a moment to consider the pros and cons…
Pros and Cons
Q. “How do I know if wicking beds are right for me?”
Let us level with you here. Yeah, we sell these things. And we love them. But, we’re not interested in selling them to anyone where it’s not the right solution. Jeremy (our sterling Wicking Beds Manager) needs some days off to practice his drumming anyway. So this is our truest, honestest, bestest list of the formidable pros, and some realistic cons of wicking beds. So read on, to help decide whether or not wicking beds are the right choice for you.
- Easier gardening. In the garden, overwatering can be just as big an issue as underwatering. With wicking beds, the observation pipe eliminates the guesswork of knowing when and how much to water!
- Happier, healthier, more productive veggies. Veggies love wicking beds because they a provide low-stress environment of constant, optimal moisture, good for soil life, and good for your plants. You’ll get more food, from less space! Here’s an easy visual to help:
The Wicking Bed H2O sine wave
- Less weeds. In wicking beds, the surface of the soil is relatively dry, making it more difficult for weeds to germinate.
- Use less water. Oh, we haven’t mentioned this yet? Wicking beds flourish with a lot less water than normal raised beds. Think something in the ballpark of one third to one half less water for each kilogram of produce.
- Water less often. Wicking beds need watering much less often, meaning plants will survive and thrive for days, or even a couple of weeks, even if you go away during in a heatwave.
- Grow on any surface. Wicking beds are a great solution for spots where eucalypt or other vigorous tree roots might invade the bed. As water and nutrients are prevented from soaking through the bed base, the trees won’t even realise the veggie bed and its rich soil is there! Wicking beds can be built on top of concrete, paving or contaminated soils, while keeping the soil in the bed separate from what’s underneath.
- Trickier to install. Wicking beds require some technical understanding and skill to be built properly; they can leak, or over-saturate the soil, either due to poor design or being installed incorrectly. (Our kits are designed to make it easier and come with clear instructions though, so you get it right the first time!)
- More expensive. Wicking beds typically cost a bit more to set up than non-wicking beds.
- More materials. Wicking beds generally require some non-renewable materials, i.e. poly pipes and liner, as well as screened crushed rock which is probably fairly energy intensive to produce. (We minimise this by using food-grade poly liner, and poly components, rather than PVC, for human health and environmental reasons.)
- You can break them (if you try hard enough). Wicking beds are not quite idiot-proof once installed. For example, it is possible to pierce the liner if you drive a tomato stake into a wicking bed too deep and enthusiastically. Trust us, we’ve repaired damaged beds, and it’s not fun to dig everything out to replace the liner!
- Some training required. Wicking beds do require a little bit of knowledge or training to be used properly – what we mostly mean here is keeping the water level topped up through the inflow pipe rather than surface watering, draining the reservoir occasionally, and not hammering in tomato stakes… It’s actually very easy! But they may not be appropriate if a wide variety of untrained people manage the beds.
If you think they are for you, you can jump straight to checking out our kits, or contacting us about installation services.
They just work!
Ok, so you do want to consider your options, but here’s what one client, Rosalie, said about her beds:
The original two wicking beds were so successful that I had the other three converted. One of the original two was planted with silver beet when I went away in Sept 2014 and another non wicking bed also planted. I was away for four weeks. When I came back the difference between the two beds was amazing. One was lush, the other just OK. This was what convinced me to convert the other three.
As for water usage, they are a miracle. I have only a 3000L tank and it would regularly run out in the first month of summer. Since the wicking bed installs I have had two summers and the tank hasn’t run out for either. I know this has a lot of other variables like temperatures and rainfall, but anecdotally they save water. I fill them once a week, or twice if we have baking heat in the high 30s+. It takes far less time to fill them than if I had the dripper system running – i.e., minutes as opposed to hours.
@ VEG Wicking Bed
The reason we recommend and install so many wicking beds is that they work. In Melbourne’s hot dry summers the veggies continue to thrive with a fraction of the water otherwise required. On the two occasions we have installed or converted one or two of a larger number of raised beds as wicking, the customers have both in short order got us back to convert the rest. The difference in plant health and growth is just so stunning.
Getting a Wicking Bed
Righteo then! If you’d like a hand getting your wick on in your backyard, then there are three main ways we can help:
- Go it alone option. First, if you are anywhere in the world, you can read and apply for yourself our unique process of installing wicking beds: How to Make a Wicking Bed (free – yay!)
- VEG Wicking Kits option. Second, for anyone in Australia, we can post you one of our wicking bed kits (including detailed instructions) so you can convert or build your first wicking bed knowing you have the right components.
- Fully installed option. Third, for anyone in Melbourne, we can come and fully install raised wicking beds at your place where we supply everything (if you want we can even supply and plant the veggies). Alternatively, we can come and convert your existing raised veggie beds to wicking in most cases. Just drop us a line!
by Rob Avis
Wicking beds are a unique and increasingly popular way to grow vegetables. They are self-contained raised beds with built-in reservoirs that supply water from the bottom up – changing how, and how much, you water your beds. In this article, we’ll talk about how wicking beds work and why we love them. We’ll also show you some great examples and leave you with ideas and instructions for creating your own.
How Wicking Beds Work
A wick works through capillary action – the same force you observe when you dip a piece of tissue paper partially into a glass of water and watch the water climb the paper. Wicking occurs in many materials; cotton, wool, geo-textile, soil, gravel and even wood to some degree. Every material has different wicking properties which you can test by placing that material into a glass of water and watching the water “climb” up. When one end of the wick is saturated and the other end is dry, it creates a moisture gradient, which drives the wick until the gradient no longer exists or you run out of water. With the earth box, one of the more popular examples in North America, the soil is suspended above the reservoir with wicks dangling into the reservoir pulling up moisture. As the plants use the moisture in the soil, it creates a moisture gradient (the soil is drier than the reservoir) which drives moister through the wick into the soil.
Advantages of Wicking Beds
Wicking beds have a lot of advantages over standard raised beds and in-grown swale-based gardens:
- They are water-efficient! Watering from the bottom up prevents evaporation of surface water (which occurs when you water beds from the top).
- They are self-watering! Wicking beds are an especially great system to use in community gardens because they save people from driving every day during hot weeks to water their beds. A full wicking bed should irrigate itself for about a week.
- They can be placed close to the house without risk of flooding your basement, since the water is contained in the bed. This makes wicking beds a great alternative to swales on properties with sump pumps or basement water issues.
- No evaporation means no salting of soil. If you are watering your soils from the top with hard water, you risk accumulating salts, because the water evaporates and leaves the minerals behind. Eventually your soil will struggle to support plant life.
- They provide a lot of drainage in the event of a large downpour.
- Since they’re raised, they will warm up quicker in the spring.
- You can easily attach cold frames to them.
- They are great for people with less mobility and strength as you don’t have to haul heavy water containers.
- By using an intermediary tank, you can automate the watering process… but more on that in a future blog.
Disadvantages of Wicking Beds
Wicking beds do have some disadvantages as well:
- They cost more to install than in-ground swales and standard raised beds.
- They will freeze sooner in the fall than non-raised beds.
- There are additional freeze/thaw considerations that need to be taken into account, which is not required for conventional gardens.
Types of Wicking Beds
Reservoirs with Media
Most of the DIY sites for wicking beds focus on building beds that use media, a layer in between the soil and the water reservoir, as their wick. This is an easy and cheap way of supporting the soil on top of the reservoir. Gravel is the most common medium, but there are a number of materials that do the trick. Here’s a good DIY blog on media wicking beds.
Beds without media require a false bottom that will allow the soil to be suspended above the water reservoir. Again, this wick system can be made from a variety of materials. Here are some examples of media-less wicking beds:
- Global Buckets
- Earth Box
Design Considerations for Media-filled Reservoirs
When designing your wicking bed, it is important to keep the depth of the media-filled water reservoir at or below 300mm as the capillary action struggles to lift the water higher than that. The soil above the reservoir acts as a wick as well, so it is important that the soil layer stay between 300 – 320mm. The soil could technically be deeper than this, however, the soil at the top will likely be much drier than the lower soil, so you’d want to make sure to that the plants you use can access this deeper soil moisture, like tomatoes, which can buried deep into the bed. Once you have determined how deep your soil and media is going to be, you need to create a containment device. There are many ways of doing this, for example, in our last blitz we experimented with four different techniques: the global bucket, a food-grade plastic tote, above-grade planter boxes, and an in-ground wicking bed.
A key element of the containment device is the overflow pipe. This pipe allows water to escape once it reaches the top of the media, ensuring you don’t drown your plants with too much water.
Above-Ground Planter Box
Because saturated soil is so heavy, we designed the beds the same way that concrete forms are designed. A carpenter friend of mine recommended that we use “whalers”, which are 2x4s with the thick end perpendicular to the plywood, and bound together using a lap joint. See the photo below. These whalers were spaced around the box to resist bending and bowing of the heavy soil. Pressure treated plywood was used to prevent rotting on the inside of the whalers and increase longevity, and then the whole box was clad with cedar fence boards. Ordinarily I don’t like to use pressure-treated wood in gardens, but since this bed was to be lined with plastic, the wood will not come in contact with the growing medium. Originally I was going to use pond liner, but it was cost-prohibitive at $0.90/sqft, so I decided to use 6 mil builder’s poly instead.
Layers in The Bed
- Landscape fabric stapled to the wood which protects the poly from sharp edges.
- Poly liner.
- Landscape fabric on bottom of bed to protect poly from punctures from the gravel.
- Weeping tile to increase rate of water communication in bed as well as reservoir capacity. If you have a long enough weeping tile you can bend it up the side of the bed and use it as a water fill pipe.
- Drainage pipe the length of the bed to encourage even drainage from the bed. This pipe is connected to the bulk head fitting and has holes drilled in one side facing down.
- 300 mm or less of gravel. Note you want to make sure that you have enough gravel to cover the weeping tile as you want to make sure that the gravel is in contact with the soil, not the weeping tile.
- Landscape fabric to segregate the soil from the gravel and preserve the pore space in the bed.
- High carbon soil
To account for the freeze/thaw issue in this climate, I set my drainage hole to the bottom of the beds so that I can drain the bed before winter. The amount of water held in the bed is determined by an elbow and stand pipe which can rotate on the outside of the bed. I like this method of water control as it allows me to infinitely control how much water the bed can store.
When it comes to raised wicking beds, cheaper alternatives to the raised wood boxes are food grade 1000 L totes cut in half. We decided to use this method for our passive solar greenhouse as these tanks were inexpensive (they cost me roughly $100 each, and one tank cut in half can make 2 wicking beds). This is far more affordable than the wood variety, which are roughly $600 each, not including the time they take to build.
Layers in the ICU
- Weeping tile to increase the rate of water communication in the bed as well as reservoir capacity. If you have a long enough weeping tile you can bend it up the side of the bed and use it as a water-fill pipe.
- 300 mm or less of gravel. You want to make sure that you have enough gravel to cover the weeping tile so that the gravel is in contact with the soil and not the weeping tile.
- Landscape fabric to segregate the soil from the gravel and preserve the pore space in the bed.
- High carbon soil
In-Ground Wicking Beds
For our blitz we built one in-ground bed. The in-ground bed is cheaper than the other two because you use the earth as the support for the water reservoir. This means you only need a containment device for the soil above grade. For our bed we chose to use cedar planks to build the above-ground bed and we made a small dugout to contain the gravel. To allow the excess water to spill out, you need to make sure that the water can leave the bed either with a designated spillway as we did, or just raise the bed up on shims so the water can leave the periphery.
Layers For The In-Ground Bed
- Landscape fabric on the soil to protect the poly from holes.
- Poly liner.
- Landscape fabric on the bottom of bed to protect poly from punctures from the gravel.
- Weeping tile to increase both the rate of water communication in the bed, as well as the reservoir capacity. If you have a long enough weeping tile you can bend it up the side of the bed and use it as a water fill pipe.
- 300 mm or less of gravel. You want to make sure that you have enough gravel to cover the weeping tile so that the gravel is in contact with the soil and not the weeping tile.
- Landscape fabric to segregate the soil from the gravel and preserve the pore space in the bed.
- High carbon soil.
A Neat Blog on In-Ground Beds
Milkwood Permaculture has pioneered an in-ground wicking bed using builder’s plastic and a round galvanized culvert ring. We have also seen people use stock watering tanks.
We chose to use a garden mix from Western Canadian Compost which is combination of loam, compost and peat. I was really impressed with the quality of the soil and I will give updates on the results over the course of the summer.
We selected gravel as our resevoir/wicking material. Generally speaking, gravel has about a 33% pore space which means that 1 cubic meter of gravel in a container will only have enough room between the gravel to hold 333 litres of water.
We also used 4-inch weeping tile in the bottom, which increases the amount of water that the bed can hold (because it is hollow) and increases the rate at which the gravel bed disperses water. The dispersement action of the weeping tiles ensures that one side of the bed does not get initially over-saturated. The weeping tile also doubles as the watering pipe.
There are all sorts of design elements that can be added or modified to change how the beds work. One popular tweak is to insert a worm composting tube into the soil portion of the bed. Food scraps can be added to the tube for the worms to process, and the resulting vermipost and worm juice will be distributed throughout the bed keeping the nutrient levels high in your soil. The worms also help to keep the system aerated and therefore prevent the system from going anaerobic. I do not think that the red wriggler can survive our cold winters, so I would recommend having an indoor worm system ready when it starts getting colder out, so that you can keep them alive until the next growing season.
As my students know, I am a big fan of cover crop systems. Typically I recommend nitrogen fixing legumes that build carbon and nitrogen into the soil through their root systems. Since these wicking beds are segregated from the subsoil, strategies are needed to keep up soil fertility. This could include cover cropping or the addition of compost, blood and bone, and rock dust. Cover cropping also reduces weeds, shades the soil, and provides a built-in mulch system.
As you can see, the sky (or the soil) is the limit when it comes to wicking beds. They are an effective and water-efficient DIY gardening implement that can be created and adjusted according to your budget, materials, space, and garden plan.
Even though we’ve built our fair share of wicking beds now and have gained a great deal of knowledge from other people’s designs and experiences, we are still learning as we go. Stay tuned throughout the summer for updates on our wicking beds, and hopefully you can learn with us!
Building a Wicking Bed
SOPHIE THOMSON: I’m really happy with my vegie patch, but after two years and constantly adding organic matter to the soil, the soil’s still not as good as it could be and I expect it will probably take about 5 years to get to that point and the other thing is, in the summer weather, I’m having to water daily.
But what if you want a vegie garden that’s easily maintained, uses very little water, doesn’t take much space and is quick to set up? Then you probably want one of these. These are wicking beds and over summer, these three have been providing me with truckloads of vegies. Today, I’m going to show you how easy it is to set one up.
Wicking beds water plants from below rather than above. It’s basically a container with a water reservoir at its base. Moisture is drawn up through the soil via a process called capillary action or wicking. This allows moisture to be more evenly distributed through the soil, creating better growing conditions for the plants.
You can build a wicking bed out of any sort of container, but what I like to use are these old wooden vegetable crates. I managed to get them from a local market gardener for just $15 each which is great value.
Other things you’ll need is a couple of pieces of old carpet to line the bottom. I’ve also got some builder’s plastic and that will line the thing and make it waterproof. I’ve got a piece of geotextile fabric. Now you can also use old shadecloth in place of that and then you need some sort of scoria or gravel that will fill the bottom of the reservoir. I like to use scoria cause I find I can pick it up for free from people wanting to get rid of it. I’ve also got a piece of pvc pipe and an elbow. Now I bought this from the salvage yard and I’ve also got an old metal cap that will go on the top. This is how we get water into the reservoir and the cap means that no mosquitoes can get in and breed in the water reservoir. I’ve got a piece of aggy pipe which I’ll join onto the inlet and that will coil around in the bottom. There’s a piece of pvc to act as the overflow point – but the most important thing is really good quality vegie garden soil. This is high in organic matter and that is essential for the bed to wick.
You need to put your wicking bed where it gets full sun, but most importantly, make sure that it’s level. Because I use these old vegetable crates, I always check for protruding nails first and hammer them in if I need to. Next step is put a layer of carpet down in the bottom of the crate and then in goes the black plastic. This bit is a bit awkward and messy but I like to try and get it as neat as I possibly can.
Now while I’m building the beds and lining it with black plastic, I find it easiest to hold the black plastic in place with some good clamps. A second layer of carpet goes on top of the black plastic and up the sides a little bit. That’s designed to stop the scoria from puncturing the black plastic.
I’ve put 100 mill of scoria on top of the carpet to hold everything in place. I’ve connected the ag pipe to an upright pipe and that’s how I’m going to get water into this reservoir. Now I’m just going to lie this pipe by the edge of the crate and coil the ag pipe in the bottom. I might even hold the end in place with a paver while I backfill with scoria.
The next step is to put it the overflow point. I’ve already drilled a hole where the scoria meets the soil. This will stop the soil getting super saturated and it’ll also give me about 30 centimetres depth of soil. That’s the optimal height to get soil wicking properly. Any more than that and it doesn’t work well and so I’ll simply insert this piece of pipe from the other side and now we simply put a layer of geotextile fabric down, above the scoria and that will stop the fines of the soil clogging up the water reservoir.
And now it’s time for the soil. Now the last step – and the one that’s always the most fun, is to start to plant it out. Now the soil will take a little while to start to wick by itself – a week or so – so until that point, you will need to water from above, just keep an eye on the soil and make the decision when they’ll cope by themselves. But be warned too – once you’ve built one of these things, it’s quite addictive and like me, you mightn’t be able to stop at one!
Wicking beds and raised garden beds play an important role in urban agriculture, which has made a significant comeback in recent years. The price of dirt is high in big cities making it cost-prohibitive to dedicate a plot of land to food production. Whether on rooftops or in a neighborhood garden, self-contained garden beds are the go-to-solution for food growing in urban environments. The U.N. Food and Agriculture Organization reports that 800 million people grow fruits, vegetables, and raise animals in cities across the planet. These efforts produce an impressive 15 to 20 percent of the world’s food. In Toronto, Canada, regulations are already in place requiring new buildings over six stories tall and with over a specific number of square feet of floor space to have at least 20 percent green roof. Toronto is North America’s second best city for building green roofs, with only Washington D.C. building faster. While other cities may follow suit and incorporate architecture and agriculture—agritecture—into their building codes, many locations around the world actively grow food on rooftops.
Wicking Beds and Raised Garden Beds are an Essential Component of Urban Gardens
Green building practices continue to gain popularity with several organizations offering ratings and certifications. The United States Green Building Council (USGBC) developed a multi-tiered rating system for the built environment, which continues to garner international recognition. Moreover, while many construction methods are beneficial to the environment, one of the most practical solutions, and perhaps the greenest building practice, is the construction of living buildings. The idea that buildings can provide shelter, integrate day-to-day human interactions, and leave space for growing plants, is a relatively new concept. Meeting all of these goals is most easily achieved during the design and build process. For example, building engineers must factor in the additional load on a building. They have to answer the question: Can the structure withstand all of the materials—soil, water, and infrastructure—for a green roof or rooftop garden? Water, nutrition, and care are all needed for successful plant growing. Wicking beds and raised garden beds are two great options for building a long-lasting and flexible urban gardening system. Both systems require sturdy long-lasting liners and are an effective way to keep plants alive and healthy while growing on rooftops.
How Are Wicking Beds Different Than Garden Beds?
Wicking beds, a subset of raised garden beds offer a few advantages and disadvantages. Wicking beds constructed with waterproof linings hold a reservoir of water at the base. Water is drawn upwards to the surface of the bed through soil osmosis and the roots of the plants in the bed.
- The concept is to build a self-watering raised garden bed that functions through capillary action
- The actual bed can be constructed in a number of ways, but they all work on the same principles of drawing water up from below the soil
- Building a wicking bed is complicated process and requires a higher level of building skills
- Wicking beds are a good choice for rooftop gardens and balconies, as they are self-watering to an extent and lower the amount of attention necessary for your plants to flourish
- While you will still need to refill the wicking bed periodically it will go a long way in helping the plants grow with less supervision
Where Is The Best Place To Put A Raised Garden Bed?
A raised garden bed is a garden box built above ground level, usually with walls and liners built into the infrastructure. A raised garden bed can be built essentially anywhere there is floor space, regardless of material. This makes it a perfect candidate for rooftops, balconies, and other city buildings as you can even install them directly on concrete or asphalt. Garden beds also have the added benefit of absorbing rainfall, which can help lessen the load on storm drainage systems during rainy winter months. The best place to put a raised garden bed can be almost everywhere with sunlight, as long as you have the floor space. Additionally, a good liner will keep the soil and plants separated from the floor beneath the bed. The trend to grow food on rooftops and in community gardens addresses the need to create a more sustainable food system for growing populations. Overall wicking beds and raised garden beds are a great addition to urban planning. With a little work, and in the right climate, urban gardens can potentially produce a variety of crops and plant types.
How to Build a Wicking Bed
All life, whether in plant form or otherwise, is made up almost entirely of water and relies on it more than anything for survival. We ourselves begin life at our most water condensed version – approximately 75-80% of the stuff – but then develop more dry matter and regulate to 65-70%. Having once been obsessed with Survivorman, Les Stroud, I know that we can survive more than three weeks without food but less than three without water. This makes a few millimetres of moisture condensed overnight on a tarp a more valuable proposition than a mouthful of miniature rock crabs.
Plants however trump us and are made up of around 80-90% water. It’s a statistic that always reminds us that, while we may forget to do any number of things in the garden, the one thing we mustn’t forget is to water. This unfortunately is never the case. The simple truth is that we’re constantly forgetting to give our plants the one thing they are screaming at us for, and for those joking about having black thumbs of death – do you see your plants laughing? No, nor can your hear their piercing shrills and cries for hydration.
We truly believe that there is no such thing as a bad gardener, only a forgetful waterer. We often don’t have enough time to shower ourselves in the morning – yet alone our plant friends – so we need to find more foolproof methods of getting moisture to the garden. This is the strength of a wicking bed.
Everyone will remember the year 3 science experiment where a tissue was dipped into a glass of water and the moisture ‘wicked’ up through the fabric, defying gravity. This is the process of capillary action and fundamental to the function of a wicking bed. Otherwise known as a ‘self watering garden’ – no, not the mirage in the desert it sounds like – wicking beds pull water into the soil from a reservoir below. The plants can then decide how much to use and when.
A wicking bed has a number of advantages over traditional irrigation system, particularly with this ability to ‘self-water’ without the aid of an expensive control timer. And unlike those systems that need to be programmed by a person trying to foresee the plants’ needs, a wicking bed feeds water directly to a plants’ roots when they require it. There is little wastage of water through evaporation, which is further minimised through good mulching practices.
Most experts set the maximum depth of soil for a wicking bed at 25cm – this being the maximum distance water is able to be pulled up through the soil. Considering most vegetables and herbs need about the same soil depth for their root growth, it seems a readymade match. We also allow 25cm of depth to hold the water reservoir below. A large body of water to draw from will make it more effective over a longer period of time, such the couple of weeks you leave your plants alone over the Christmas holidays. So when building one a vessel that is approximately 50cm deep is ideal.
When creating a wicking bed the first step will involve lining the base (what will become the reservoir) with a non-porous, rigid liner that will hold the water. Make sure it is pushed snuggly up against the walls and into any corners, so there is less pressure on the material once filled with scoria and water. Any small punctures or splits will leak water and be painful to fix – very painful indeed – so be careful when handling. If you’re looking to do this part on a budget, you can use a thick builders film but you should play it safe by double layering. Otherwise, a pond liner will be more foolproof, albeit it more expensive.
Next come the components that feed water in and out of the wicking bed. An inflow channel, that will be used to fill up and then top up the reservoir, should lead to the bottom of the wicking bed and sit on an inch or two of scoria. To create this leader channel we use 50mm PVC piping which is fitted to a length of slotted agi-drain to allow the even flow of water in. Stagnate water sitting in the reservoir may attract mosquito and their larvae, therefore the inflow channel should be capped when not in use. Next, and most importantly, secure an overflow valve to the side of your vessel. This dictates the depth of the reservoir and, as mentioned earlier, should be no more than 25cm from the top of your wicking bed. When you fill up or top up your reservoir, water overflowing from this valve indicates your wicking bed is full.
Now fill up the reservoir with a fine grade scoria, which is a porous volcanic rock available from all landscape supply yards. This not only makes the reservoir a solid platform onto which you can then add soil, but helps aerate the water and makes for more effective capillary action. The finer the grade of scoria, the better it does these jobs and the less potential there is for punctures of your reservoir liner.
As you fill up with scoria, we like to put ‘wicks’ – like those on a candle – that will pull water from the lower parts of the reservoir to mid points of your soil. For this we use strips of a fabric called geotexile, (which is very much like felt) because it is made up of small, dense fibres that wick incredibly well. Although the soil will do this job fine by itself, these will make the system work better when the reservoir is at low levels, which may buy you extra time on your summer holiday; system may not need a top up for three weeks rather than two.
Finally it is time to add a growing medium for our plants. Wicking bed systems tend to favour soils that have high levels of organic matter and compost (generic soils found in garden centres tend to compact up and prohibit the capillary process) so it is worthwhile investing in good quality compost and potting mix. We have also found the benefit in adding 1 part perlite to 10 parts soil, which helps in reducing compaction over time. To keep the soil out of the reservoir we also use the geotextile fabric. Lay a sheet on top of the scoria and attach it up the sides of the wall using a staple gun. Of course don’t staple it in the reservoir section unless you want to put holes in liner!
This enclosed style of growing means that there is very little wastage of water as it is constantly recycled through the system until it is used. Such is also the case for the nutrients, which can be fed in liquid form directly to the reservoir. It does however mean that the water can become a little funky – algae can build up and make it toxic to plants – and so you should flush the water through the system every 12 months.
Although they are commonly referred to as self watering gardens they are not silver bullets. All young plants will need surface watering to begin. If you’re worried about over doing it at this stage – don’t – any extra water will come out of the overflow and by using a good quality soil mix it won’t become saturated. Once the plants are about a month old, the self watering affect begins to kick in. And remember, that while you may be impressed with your garden’s ability to water itself, pests such as possums, rats or birds, couldn’t care less.
So while wicking beds will take care of a large chunk of the watering part, they will not do everything for you (we’ll have robots for that soon) and shouldn’t stop you from spending more time in the garden.
If you’d like a little veggie patch co staff member (almost as efficient as a robot) to install a wicking bed for you, you can find the details here