How to Make a Wicking Bed
So let’s get down to brass tacks. (Actually keep those away from your wicking bed liner!) But let’s see how to build a wicking bed from scratch – and how to take care of it.
If you haven’t already checked them out, you might want to see our pages on:
While on this page you’ll find:
The VEG Approach to Building a Wicking Bed: A Step by Step Guide
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 and then let’s go through each bit, step by step, in the order we actually install them.
You’ll notice that we add this, that and the other.
Step 1: Create your raised bed
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 (yes, as a matter of fact we do sell kitsets which come with full instructions we won’t bore you with here).
Step 2: Installing the liner
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.
Step 3: Creating the overflow
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 invented all by our little selves! With a little swivel of the pipe you can drain the water out periodically to prevent stagnancy.
Step 4: Making the water reservoir
Add the stones and 50mm diameter perforated inlet aggy (agricultural) pipe. We have found 7mm or 1/4inch 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 for our needs.
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 5: Test for leaks
Test with water and ideally leave overnight to check for any leaks.
Step 6: The soil
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.
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.
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 back then, 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):
Ok, now that’s a brief 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.
Getting the Right Stones and Soil for Your Wicking Bed
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, aggregate, screenings, quarter minus, road base, are some of them. But not gravel. Gravel is typically too course, in that the individual bits are too big. In our experiments we have found that going above 5-7mm in the size of the pieces means you lose the wicking function of the stones. Here you can clearly see the soil wicking up the stones – up to about 10 cm in our experiments.
Sources for your aggregate
Wherever you are based try your local landscape supply source and ask for Quarter Minus or 7mm bluestone screenings; for Melbourne metro installations we often use Bulleen Art and Garden or Fultons Garden Supplies.
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.
Sources for your soil
Wherever you are based try your local landscape supply source and ask for a good organic mix for veggies; for Melbourne metro installations we often use Bulleen Art and Garden’s veggie mix, or Fultons Garden Supplies and their 5 Way mix. It can be well worth checking the pH of your new soil to ensure it’s in the sweet zone (i.e., around 7) for your new seedlings (many a time we’ve seen an out-of-balance pH stall the growth of fresh plantings). You can source a pH kit form your local hardware and they are very easy to use.
Managing Your Wicking Bed
Managing a wicking bed is dead easy. The main thing is to check the reservoir water level regularly and top up as required (by shoving a hose into the inlet pipe and turning it on until the reservoir overflows).
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.
Common Wicking Bed Mistakes
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.
Forgetting to install an overflow pipe
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:
Getting the dimensions/ratios/materials wrong
A final group of errors made in wicking beds is to do with either using inappropriate materials 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 it will get too wet. Too deep and it won’t get wet enough. The water layer really needs to be at least 15cm deep to justify the effort of building the thing, and ideally at least 20cm deep.
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 as outlined on this page (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!