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Building a wicking bed

A wicking bed – not your average garden bed

Which way does water flow? Up! In a wicking bed it does anyway. A wicking bed is a special kind of veggie bed that contains a water reservoir at the bottom, watering the roots of the plants from below. The water moves up by ‘capillary action’ – just like fuel moving up the wick of a kerosene lamp.

The plants don’t need overhead watering – you just keep the water in the bottom topped up, by filling the pipe coming out the top of the garden bed. Fill it just until water starts to flow out the overflow pipe on the side – this means the reservoir is full.

Jeremy demonstrates how to water a wicking bed. A little too much water! When the overflow pipe um… overflows, it’s time to stop watering!

Why use a wicking bed?

  • Wicking beds use up to 50% less water than conventional veggie gardens as less water is lost through evaporation
  • Wicking beds are low maintenance, as the plants can survive days in the heat of summer without a top up
  • The plants are often noticeably healthier – they love the low stress environment of constant moisture provided by a wicking bed
  • Weed problems are less because the surface of the soil, where weed seeds germinate, is the driest part

Wicking beds do use extra resources though, in the form of plastic liner and plumbing parts. And things can go wrong, such as for instance, not that it’s ever happened to us… no, never… someone in a community garden for instance might put a tomato stake through the liner! It’s quite a job to dig everything out and fix it. But in a lot of cases the pros outweigh the cons.

Build a wicking bed in a few (fairly) easy steps

Check out the below diagram of a wicking bed and then let’s go through each bit, step by step, in the order we actually install them.

Step One

The first thing is to create the edging or container the water and soil etc will sit in. In our case this is a raised bed 40 or 60cm high made from cypress macrocarpa timber sleepers.

Michael raising some VEG beds with Cypress macrocarpa.

Step Two

The next thing is to get the liner in. Real careful, like. We talk about the liner (drinking-water certified) we use below, but if the liner you use is thin, maybe double it up, or put a cushioning layer of sand or similar below it. Here and in the next step more than anywhere take your sweet time.

The waterproof liner is in!

Step Three

Now we usually add the outlet by drilling a hole through the bottom of the bed at one end then cutting through the liner and inserting the three-way water level indicator, overflow, and drainage outlet system we (Very Edible Gardens Wicking Beds) invented all by our little selves! With a little swivel of the pipe you can drain the water out periodically to prevent stagnancy.

Drainage Hole going in at a permablitz

Step Four

Add the stones and 50mm diameter perforated inlet aggy (agricultural) pipe. We have found 7mm or ¼” bluestone screenings are the ticket, or pea gravel (though it’s harder to get and costlier), having experimented with sand and various other mediums. The main issue with sand, we have found, is that it compromises the speed at which water can move into the reservoir when filling, which can create a back-flow issue and mean you have to have the hose on trickle. A secondary issue is that sand usually carries fine particles with it, which can clog the system over time.

Note that the inlet aggy pipe needs to be longer than the outlet aggy as per our diagram. The reason is you want to get the water in fast as possible (as in a hose on full tilt) without backflooding up the inlet pipe, so we make the inlet aggy section as long as the bed itself (often winding about – the pipe has curve memory – which is great as it means more inlet run length), then a short outlet section adjacent to this. The stones in between inlet and outlet aggy’s prevent water rushing through and out the overflow before filling reservoir, but allows fast fill without backflooding, which is really important. There’s no need to have a long outlet aggy pipe, as it will flow fast enough even with hose on full without causing problems.

Finally you want the inlet pipe (what you stick the hose into) on the same side or end of the bed as the outlet/overflow riser/water level indicator so you can see the water level, or at least see it spilling whilst filling so you know when to turn the hose off.

Step Five

Test with water, and ideally leave overnight to check for any leaks.

Step Six

Add the geotextile fabric layer (some folk use a double shade cloth – this layer needs to let water up but prevent soil moving down). Now add the soil as you would a normal raised bed (ideally a fairly porous loam that is not too heavy in clay or organic matter). You are also now ready to plant your plants. Also don’t think that just because it is a wicking bed that you can plant small seedlings then forget about them – seedlings will often still need supplementary watering for the first week or two until they get over any transplant shock and get their roots down into the soil moisture zone.

Detailed Video Clip of the Whole Process

VEG’s Carey talks through the entire start-to-finish process of building a VEG wicking bed and all the above steps. Note here we used scoria which is what we had even though it is not as ideal as the alternatives we mentioned above. Also, you don’t have to staple the liner to the inside of the bed if you’re careful when filling with stones; this reduces the chance of tearing the liner – you can just let the weight of the stones and soil hold it in place): Click here to watch the video.

To find out more you can check out Very Edible Gardens’ dedicated website: www.WickingBeds.com.au