Judging by the stats I get for this site, there’s a lot of interest in the whole concept of wicking beds & boxes, so I thought I’d show just how I put these things together. Of course you can use any type of container you fancy; the principle’s the same.
The general concept of water-wicking can be found here. I don’t have the level ground for a wicking bed and didn’t want to do all that work anyway, so the tubs & boxes are ideal for me as they can be poked into any small space.
Here’s a tub and a box (actually sold as a storage ‘crate’). Also in the photo are a circle of heavy duty plastic and a couple of plastic tubes (more on those later):
I get these from Bunnings (for non-Aussie readers that’s our local big-box hardware store). The crate is 60 litres in volume, 60cm long, 40cm wide and 25cm deep. I’d have preferred something a little deeper, but couldn’t find it, so that’s where the tubs come in. I don’t know the volume of the tub, but it’s 50cm in diameter and 40cm deep. It’s a typical plant pot, so it has drainage holes in the bottom; something needs to be done about that. The crates have no holes (you make your own, where you want them).
You’ll need a supply of good friable compost. Ordinary garden soil is not good enough. Some compost worms from a worm farm would be useful too.
For the wicking-box: I drill 2 holes, one at each end of the crate and about a third of the way up from the bottom. The holes are about 1cm in diameter. Initially I made them too small and they blocked up with soil, so I increased the size. These are where excess water drains out. The short plastic tube pictured is stood up in one corner of the crate and the crate is filled with compost. Water is added through the tube. Make sure you put the crate in it’s final position before you do all this because you’ll never lift it when it’s full (unless there are two of you, of course—even then it’ll be an effort).
If you want the crate up off the ground a bit then you can put it on something. I use those white polystyrene fruit boxes from the local greengrocer. I need my boxes up high because I have wild rabbits which browse everything they can reach down to the ground. Make sure it’s solid. They’re heavy; you don’t want the whole lot collapsing on you (or on the cat, which would be worse—for the cat).
Put a few compost worms in the box for aeration and you’re ready to go. They will eventually turn the compost into worm castings and this will enrich the mix even more.
Here’s a photo of the corner of a box with the watering tube in position. I’m showing this because there’s a frog at the top of the tube. He seemed to like living in the tube and stayed there for several weeks. I watered the top of the box during that time instead of adding water down the tube as he wasn’t partial to the sudden cold drenching. He seemed to like to sit at the top of the tube during the day when the sun was out. After all, who doesn’t like to feel the warmth of the sun on their back? I never found out what species he was. He seemed a bit big for a tree frog (we have the Whistling Tree Frog and the Southern Brown Tree Frog here, and he was always hunkered down, so I couldn’t see his tiny toes) and a bit small for a Pobblebonk. I never heard him call, so ‘he’ may have been a ‘she’.
The wicking boxes are ideal for most vegetables. I’ve had huge successes with dwarf beans and if you put some sort of trellis behind the box you can grow climbing beans as well. Capsicum, broccoli, kale, bok choy, silver beet, small bush tomatoes like Roma or San Marzano, lettuce, celery (celery loves wicking boxes because of the constant water supply)—all these do well. I haven’t tried carrots or leeks (because I blanch leek stems with deep mulch and there’s not enough depth), but this year, for the first time, I’m trying garlic. Herbs, like basil, chives & parsley do well, too.
Watering is supposed to be done through the tube. Initially it works, but as the compost in the box starts to turn into soil and becomes a bit more compacted, it takes longer for the water in the tube to soak into the mixture, so often I just water overhead. The tube is still needed to see where the water level is in the box (use a dipstick of some sort). I only need to water about once a week, sometimes even less frequently. When there’s no water showing in the tube and the surface of the mix is still moist (don’t forget to mulch well), I still don’t water. I only water when the soil at the top is starting to dry out. It depends on the size of the plants in the box, too. Advanced plants will have a higher water requirement than just-planted seedlings.
There will be a gradient in wetness through the box, with very wet, boggy soil at the bottom grading to drier, but still moist, towards the top. Roots will find their desired moisture level. Water-absorbing roots will go right to the bottom. Fine feeding roots will stay nearer the surface.
The whole concept is great for water conservation.
For the wicking tub: I wanted to try the larger tomatoes in a wicking box, but felt that it wouldn’t be deep enough for their bigger root systems. Hence the tubs. The tub is just a large planter tub with drainage holes in the bottom, so these need to be covered in some way to create the water reservoir. I cut a circle of heavy-duty plastic (trial & error for the diameter) and push it into the bottom of the tub making sure that it comes up the sides and forms a reservoir at least 30 cm from the top (if you’ve read the link above, you’ll see that water will ‘wick’ up about this distance before gravity takes over and holds it back). When the reservoir is full, excess water just flows over the edge of the plastic and out the normal drainage holes.
The plastic watering pipe needs to be a bit longer in this case, so I just tape 2 together and cut a bit off one end (see photo). Add compost and worms as before and you’re ready to plant.
Tomatoes did really well in the tubs last season, so I’ll definitely be doing that again.
Note: for the plastic watering tubes, you need to buy a length of poly pipe about 5cm diameter and cut it to length. The ones I use were scrounged from the local greengrocer. They’re from the centre of those rolls of plastic bags you tear off to put your fruit & veggies in. I have a huge boxful under the house. The local g-g put them aside for me until they went back to rolls with cardboard inner tubes (even they were good—nice and thick and burned like little logs in the fire).
So there you have it. Wicking boxes in a nutshell. Give it a try. Hope this has helped.