What is a wicking bed I hear you ask? It is basically a raised garden bed with a permanent pool of water in the bottom half like a big self-watering pot.
Here is a link to some very fine ones made in Victoria but there’s heaps of others out there, commercial & DIY. The ABCs Gardening Australia popularized them a few years ago.
Our main reference for our eventual design came from this link. We made a few changes, but the idea is very similar.
We were going to repurpose the garden beds from this company (see the prices) but found a closer one. The main differences were
- We used multiple (5) layers of cheap “builders plastic sheet” instead of a pond liner. Why 5 layers? Just trying to minimize the chance of a puncture. One layer could be enough – your risk!
- We used cheap 20mm blue metal aggregate instead of red scoria.
We got the highest beds (800mm high) to reduce bending over.
It’s too early to tell yet, but all the water delivery fittings may not have been necessary. It depends a bit on how often the tank has to be topped up. The overflow fittings are probably worth the effort rather than just a drilled hole though. We used 20mm (3/4″) fittings. The overflow required a 27mm hole saw. You could save money by drilling & filing out multiple holes.
We cut the 1st & 2nd plastic sheets as 3.2 metres long, that is 2.4m along the bottom and 0.4m up at each end. The 4m wide sheet is left folded effectively as 2 x 2m. So you end up with 4 layers at this stage. Placing the sheet is pretty tedious depending on how neat you want to be. It’s not critical. Just ensure the top is above the 370mm waterline.
Place the 2nd sheet exactly the same way.
We cut the 3rd plastic sheet as 4 metres long, that is 2.4m along the bottom and 0.8m up at each end. This time the 4m wide sheet needs to be unfolded so it has sufficient width to cover the whole wall of the bed. You’ll find each successive sheet more tedious to place than the last. Just try to even out the various folds along the top of the bed so when trimmed there aren’t thick bunched up folds with resultant big gaps between the sheet & the steel.
Now’s the time to cut a neat hole for the overflow, so that water exits the tank rather than finding a way/ getting trapped between the sheets or 1st sheet & tank wall.
Now add the layer of geo-textile cloth (geocloth) which provides puncture protection for the plastic sheet. We found it simplest to use two pieces – a bottom piece and a separate wall piece. Our roll was 50 metres long x 1m wide.
We cut the bottom piece as 2.8 metres long x 0.6m wide, that is 2.4m along the bottom & 0.2m up each end. The circumference of the tank was 4m so we cut the wall piece to be 4.2m x 0.6m which gave a bit of overlap at the joint.
Lay the bottom piece & tape it up the wall. Lay the wall piece so it now overlaps the bottom piece and itself. Note we didn’t bother to “protect” the plastic above the waterline as it shouldn’t have any sharp bits.
In order to see the water level, and as a place to fill the tank via a garden hose, we used PVC pipe, any offcut you have lying around will do. In our case 100mm stormwater, but 40, 50, 90mm will do. Contrary to other designs I don’t think it should need any holes to let the water in; water should easily find its way from underneath. BUT not shown on other designs, I found out the hard way that anchoring the pipe is important – if accidentally pulled up you’ll never be able to push it back down through the blue metal. My simple but effective anchor was another piece of (electrical) PVC pipe offcut passing through the main piece, using the same hole saw for holes. A bit of wood or steel rod or anything lying around would be effective but may rot out quicker. The pipe has a cap to prevent mosquitoes getting in.
Hold the slotted drain coil and water inlet pipe in place while shoveling in the blue metal so it doesn’t move. I don’t think the drain coil is essential, again the water should find it’s own way through the blue metal. We used 50mm drain coil & 40mm PVC pipe.
Now the fun part – gardening begins. Good luck with your wicking bed adventures. It’s too early to tell how ours will go but please get in contact if you want any more info. There’s other little details on the PVC fittings but if you’ve read this far & are thinking of building, you probably don’t need even more detail.
We’re taking a punt they will suit us really well as we’re building four of them:-
Rough bottom line cost estimate $440 (PS. add $5 for ag pipe). That doesn’t include paving that has been laid under & around the beds. Now that’s a hell of a lot of vegies that need to be grown before any savings are made. Four wicking beds? I guess not everything in life is judged on purely economic grounds.
Cost savings could be made by using a wooden frame for the bed. Maybe an apple packing crate or discarded IBC tank or other repurposed item instead of something new. There seems little point skimping on the # layers of plastic as it is not a major cost, and far less cost than a pool liner or a purpose-made wicking bed liner.