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Having introduced wicking beds and why they can be a great idea, let us get into some details. Check out the below diagram of a VEG-style wicking bed but don’t get too worried about the details as we’re going to through each bit, step by step, in the order we actually install them.
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, usually 40 or 60cm high, made from cypress macrocarpa timber sleepers.
If you’d like some pre-cut pre-drilled beautiful timber with all the screws and things you need to put it together, you can pick up one of our lovely and sustainable cypress macrocapra timber beds. While we ship our wicking conversion kits Australia wide, the timber is just Melbourne only, sorry!
The next thing is to get the liner in. Real careful like. While the liner we use is tough, you still want to make sure there’s noting sharp like screws or glass underneath it.
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.
Step 3: Adding the three purpose pipe
Our systems have a three purpose pipe which:
We add the outlet by drilling a hole through the side of the bed at one end, then carefully cutting a hole through the liner and inserting the three-way water level. It screws together and clamps up real nicely, and we add a little silicon sealant to really seal the deal.
We invented this three-way system and it’s honestly the best.
Now it’s time to add the wicking medium to make the water reservoir.
Note that the inlet aggy pipe needs to be a good length, but doesn’t have to line the full length. 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 aggie section about 1m then a short outlet section adjacent to this.
Finally you generally want the inlet pipe (what you stick the hose into) on the same side or end of the bed as the outlet (i.e. our three-purpose pipe) so you can see the water level, or at least see it spilling whilst filling so you know when to turn the hose off!
Fill the bed with water to just below the height of the screenings. We recommend compacting them a little (get in there and walk on them). Get it really nice and flat. The water should be glistening on the stones and there shouldn’t be any puddles.
Now is the time to cut the top off the three-purpose outlet pipe. You want it to be at the level of the water, which is the top of the stones. We use a pipe cutter but a Stanley knife will do if you’re careful.
Test with water and ideally leave overnight to check for any leaks.
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). You are also now ready to plant your plants.
One thing to note here. The driest part of wicking bed soil is near the surface, which is great for weed prevention. But, it does mean that small seedlings will often 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.
VEG’s Wicking Beds manager emeritus, Jeremy, takes you through the entire start-to-finish process of converting a VEG wicking bed and all the above steps. Watch or download all the videos via our Vimeo Channel, or watch the playlist on our Youtube channel. (Click the top left menu to scroll through and select the video you’d like to watch).
Ok, now that’s an overview of all the stages to building your wicking bed, and that might be all you need to know. But, we do have separate easy-to-use instructions that come with all of our wicking bed kits, that involve a little more hand-holding along the way.
A couple of the most common questions we’re asked about wicking bed builds are: “what kinds of stones and soil do I need, and where can I get them?”. This section aims to make this part of your wicking bed set up as easy as possible.
There are a lot of different words you can use to describe the little bits of hard stuff that provide spaces to accommodate the water and hold the soil up. Stones, screenings, aggregate, and quarter minus are some of them, What we’re looking for are crushed stones that have been filtered (or ‘screened’) so that the particles are all a pretty consistent size.
In our experiments we have found that going above 5-7mm in the size of the pieces means you begin to lose the wicking function of the stones. Here you can clearly see the soil wicking up the stones – up to about 15 cm in our experiments.
We use 7mm bluestone (also called ‘blue metal’) screenings which is widely available in Melbourne and some other parts of the country. If you can’t get bluestone in your area, some other hard rock aggregate in the 5mm-7mm size range should work well (e.g. granite). Your local building or garden supplies place should have something that fits this bill by the truckload as it is used for drainage, in concreting and as road base.
Search for ‘7mm aggregate’ or ‘7mm screenings’ or ‘quarter minus’ online in your area – or call your local landscape supplies and ask for that – and if your options are 5mm or 10mm, go with the smaller.
The role of the wicking medium is to have a good amount of pore space for water to be stored in, and the material needs to wick effectively. Some materials wick water better than others. But there’s often a trade off between water storage and wicking ability. We also want something that is easy to work with and doesn’t risk damaging the liner, and it has to be chemically pretty inert so it doesn’t shrink over time and the water remains clean. The following don’t fit the bill as well as screenings do:
Heavy, clay-based soils high in organic matter are not ideal for a wicking bed, and particularly for the half closest to the water reservoir. The idea is a sandy loam with moderate organic matter. Here are a some sample photos of some ideal soil where again you can see the water wicking up through it.
Wherever you are based try your local landscape supply source and ask for a good organic mix for veggies; for Melbourne metro installations we use Bulleen Art and Garden’s veggie mix (which has zoo poo in it amongst other things!).
If the soil smells a little ‘hot’ or rich it might be worth waiting a week or two for it to finish composting before planting.
All of these places by the way can get your screenings and soil on the same truck. It’s usually a good idea for the soil to go on first so the screenings come off first, closer to your beds!
Managing a wicking bed is dead easy. The main thing is to check the reservoir water level regularly in warm weather. Once it drops to below 10cm from the soil level, it’s about time to top up. Click a hose onto the inlet pipe and turn it on until the reservoir is overflows.
Don’t top it up every day though or it will be too wet. We’ve got through Melbourne summers topping them up no more than six or seven times.
It can be a good idea to put your wicking bed into ‘drainage mode’ in winter. What do we mean by that? Well if our wicking system looks like this in the warmer seasons:
All we need to do in winter to stop the bed from being too wet – in fact turn our wicking bed into a drainage system – is to turn the overflow to the side a little.
Another important reminder is to not use tomato stakes (or you may damage your wicking bed!). We tend to use A-frames, tee-pees or affix external structures to the side of the bed to grow climbing plants.
Apart from that, you plant, tend and harvest your plants as normal. Keep in mind though that you don’t want to go as hard as you otherwise might on nitrogenous nutrients (such as blood and bone). Still use them, but not in excess, as you don’t want them leaching down into and stagnifying (yes that’s right we make up new words at will) the reservoir.
You may have noticed that above we used phrases like “well built” or “properly installed” when referring to wicking beds. This is because there is a tendency out there for folk to read up on wicking beds then race out and knock one or more up in a way that makes one of the following common mistakes. Let’s review a few traps for young wicking bed players, so if you are about to have a go you can hopefully avoid them.
A common error for first-time wicking bed builders is forgetting or just not knowing to put in a designated overflow pipe, or even at least a hole where water can safely exit the bed before it raises up to saturate and eventually kill the soil life and your plant roots. This liner should be at the point of transition from soil to stones, which in turn should be about 30-35cm down into the soil profile.
The second common error creates the opposite problem – too little water instead of too much. This happens when there is a leak in the liner, or, when a drainage pipe is run through the liner such that it leaks. Either way, the upshot is that you do not have a wicking bed. You have a leaking bed, or in other words a conventional bed. So the take home here is be really, really careful about creating a leak-free reservoir. Be gentle with your liner. If you’re not using the sturdy VEG liner, but something thinner and more fragile, double it up. Lay it down on some soft sand or old carpet. Maybe even put a layer of sand or something on top of it so the stones don’t accidentally pierce it. Water cares not for a she’ll be right attitude, and makes a beeline for any hole. If in doubt, go nuts with one of those silicon sealant tubes. And test the liner by filling with water before you add the soil. Then leave it overnight and check for leaks in the morning before moving on.
Oh, and don’t even think about bashing some tomato stakes into your bed and piercing the liner as per this video of us performing a fix-it job on one of our older-style wicking beds:
A final group of errors made in wicking beds is to do with either using inappropriate materials (using scoria in the reservoir is a big one although it will still function a bit) or getting some of the fundamental dimensions and ratios wrong. The soil depth really needs to be between say 25cm and 40cm (ideally somewhere well within these two extremes). Too shallow and there’s not enough space for roots, and the soil can be too wet. Too deep and it won’t get wet enough in the upper layers of the soil. The water layer really needs to be at least 15cm deep to justify the effort of building the thing.