The knowledge of what are known as ‘water-wicking beds’ seems to be growing, with more and more gardeners putting them in place.
I first came across the concept at this webpage. There’s plenty to read there. The first three articles on how water moves through the soil and using stones (not) as a base for the bed are very important.
Following that I found a site where the writer had used white polystyrene vegetable boxes as small wicking beds. Since I have heavy clay soil in the area I wanted to put my vegetable garden, back-breaking digging was out of the question, plus it was on a slope, so the idea of small individual ‘boxes’ appealed.
I couldn’t access the number of poly boxes at the size I wanted, so searched in the local hardware store for plastic crates, of which there are a huge variety. I went for black rather than clear plastic, because algae will grow in wet soil when it can get light and I didn’t want ‘green’ sides to all my boxes. I thought the black colour would be an advantage in winter (warmer soil) but might not be so good in summer, though they could be easily shielded from the sun.
I came up with these :
They’re 60 cm long, 40 cm wide and 25 cm deep; not quite as deep as I would have liked at the time, although there are deeper ones available now, but useful for shallow-rooted plants which most vegetables are.
Water will ‘wick’ up about 30 cm against gravity so any soil depth greater than this will mean the layer above that depth will remain dry.
With the boxes I chose, at 25 cm depth, that wasn’t going to be a problem.
It’s usual, in large beds anyway, to put in some form of perforated pipe across the bottom of the bed, which opens to the surface, through which to add water. The water spreads out to fill the reservoir below the bed and this is where the water comes from to wick up into the soil above. By looking down the pipe or using a dipstick, it’s possible to see if there is water in the reservoir or not.
For a small box like I was going to use, this is unnecessary; all I did was stand a piece of pipe in one corner of the box :
And drilled drainage holes (one at each end) about one-third of the way up from the bottom :
Finally I filled the box with good quality compost, not bought stuff, but stuff I made myself, with plenty of organic matter.
I soon found that adding water via the vertical pipe didn’t work, as it was just too slow a method to fill the lower part of the box (I get little frogs making a home in my pipes and they get pretty annoyed if I suddenly dump a load of water into the pipe). So I started watering overhead and have done so ever since. It’s what happens when it rains anyway. I use the pipe simply to check on water levels. If I can see water in the bottom of the pipe, I know the soil at the bottom of the box is saturated and I don’t need to water until I can’t see any water. The boxes will go several days more without water if the plants are small and not sucking much up. Poking a finger into the top few cm will show how moist the soil is (I’m calling it soil because it’s quicker to type than ‘compost’ or ‘growing medium’, but you know what I mean).
So that’s essentially my method and I have about 35 wicking boxes around the garden at the moment.
I began reading other blogs where people were putting in large wicking beds and noticed that most were using sand or gravel in the water reservoir and covering it with a layer of some sort of cloth to stop soil getting into the gravel. I couldn’t see the sense in this; roots will go right through this and into the water below (making holes) and if there’s no watering from above this layer will be largely free of nutrients (of course rain will wash nutrients through so that’s really not a problem). I note that the person who developed the concept (see the link in the second paragraph above), seems to think likewise. My boxes are full of compost in which every root can access nutrients. The water-seeking roots will live in the saturated layer at the bottom and the feeder roots liking the medium just moist, will stay in the top section. Too much work and materials are required to do all that other stuff! Plus, I can lightly fork fresh material into a box to top it up, without the fork becoming snagged on anything below.
I also add worms from the worm farm (compost worms, not garden worms) and they continually aerate the soil and eventually turn it all into worm castings, which hold a phenomenal amount of water. I’m monitoring those boxes to see if growth is affected (the texture is like mud!) and will remove and replace at least half the medium with fresh compost if needed. If there’s a problem it will probably be due to low oxygen levels.
Another thing to note is that nutrients can’t leach away as they do in a non-wicking garden bed. What goes into the wicking bed or box stays there until the plants take it up, so it’s important not to over-fertilise or get the nutrient balance out of whack by adding too much of anything. That’s why a good, nutrient-balanced compost is essential. Being able to identify nutrient problems just by looking at the plant is an essential skill.
During the growth of a single crop, the soil level in the wicking box will drop a few cm, so in between crops I top up with fresh compost. I mulch the top of each box as well, so that direct sun isn’t pulling water out of the soil faster than it can wick up from below.
I’m happy with the boxes and even if I had a flat area to make wicking beds, I wouldn’t bother with all that work and extra materials. A wicking box or crate can be poked into any small space, on a deck or sunny porch or hidden amongst a collection of more traditional flower pots. They’re ideal for rental properties where you can’t do major gardening works and you can take them with you when you leave. For less than $20 and 3-4 buckets of good quality compost and a punnet of seedlings from the garden centre, you can get a veggie garden going in half an hour and build on it from there.
Once you understand the wicking process, almost anything can be turned into a wicking container. Old fridges, second-hand baths…..I’m currently growing my strawberries in plastic wicking buckets.
Here’s a line of 10 boxes I put in a few years ago :
I put them up on polystyrene fruit boxes to prevent rabbits accessing them. I’ve since found that a large rabbit can stand on its hind legs and nibble round the edges, so I’ve put wire around the top of each box.
They can be individually covered to keep out cabbage white butterflies or whitefly :
You can grow one type of crop per box and if necessary, adjust individual growing requirements, e.g. pH, just in that one box. This is wombok chinese cabbage in a wicking box :
Sometimes its easier to direct-sow seed rather than go through the tedious process of sowing, potting up seedlings and transplanting. This is mizuna, another Asian green. I just clip off what I need with the scissors. The chooks get a handful every day and provided I cut above the growth point, it simply keeps on growing :
I think individual wicking boxes are the best thing since sliced bread. I wouldn’t ever bother with the work and quantity of materials needed to make a full-sized wicking bed.