I am sure many of you will have seen the Wicking Garden Beds promoted on Gardening Australia from time to time. These are Rolls Royce garden beds. Its not all plain sailing though, at the end of the post is a controversial update!The beds are sealed garden beds with water in the base. Capillary action draws water up from the base into the soil, providing water for plants without waterlogging the soil. Because the water comes from ‘underneath’ there is no irrigation overflow, wind drift and minimal evaporation. Plants can access as much water as they need, and still have good drainage. If you do have a big rain event the water can drain out harmlessly from the overflow point about 30cm below the soil level.
Here is a diagram from the Ballarat Permaculture Guild which illustrates the concept
Gardening Australia recycled an old vegetable crate with a plastic liner, they swear by them but we at the RHAA wondered how they would work using a long, low water tank without a lid? Those inventive guys at Tankworks sell them, looking like this, they are plastic lined with a tap fitting to maintain the water level visible at the near end.
You can see from the photo we installed an old blanket for wicking effect, some pavers to maintain the water space and a plastic downpipe for refilling with.
We put a sheet of geotech fabric over the pavers to stop the soil dropping down. We put the soil level just below the outlet point to encourage wicking. Conventional wisdom is soil will wick up about 150mm and a wicking material like old carpet will lift much more. We needed a LOT of soil, our tank was 1.8m long and 0.5m high. We needed about half a cubic metre, that is a lot of sieved soil dug out of the chook pen!
At last it was time for plants, tomatoes, basil, kale, spinach, coriander, parsely and cos lettuce. I emptied a tray of worms from the worm farm in as well, they will enjoy the heavy mulching with cane straw, which keeps the soil cool and prevents evaporation.
December 2015 Update! After three months of riotous growth and heavy successive harvests of lettuce, spinach, cucumber, tomatoes, kale etc we hit a snag. Plant growth slowed. Expert referrals suggested improving the drainage of the media but the real problem is, I am over watering! Even in summer the bed only needs a top up once a week if we get any rain at all. Also the zucchini is taking over, those things are scary.