I’ve been using wicking beds for many years and find them a terrific way to grow vegies. The constant moisture in them has produced the best lettuce and carrots I’ve ever grown and the rhubarb in the wicking bed has thrived through the last hot dry summer (unlike its relatives in the unwatered food forest). Having a water reservoir in the wicking bed means that I’m only watering them every two or three weeks, or even less often.
I started with the most common design – gravel for the water reservoir, then a layer of geotextile, then the soil. That worked OK but the geotextile got caught up when I dug new compost through the soil and the gravel was a real pain when I wanted to dig everything out to refresh the soil.
For the last few years I have been using wicking beds with the whole container filled with a mix of soil and compost. The bottom of it is saturated where the water is held but that works fine and the plants grow well. It’s much simpler and cheaper than using gravel. But still, the vast majority of designs on the Internet use gravel.
I’ve recently completed a Bachelor of Horticulture at Charles Sturt University. As part of this degree I did a couple of units in soil science. I learned about how water moves through soil and how capillary action – which causes wicking – needs small gaps between the soil particles to work. The large gaps between pieces of gravel won’t allow wicking to work very well. So I started to wonder how wicking beds with gravel actually work, and what is really the best material to use in them.
There is very little in the scientific literature about wicking beds; only lots of opinions on the web and YouTube. So I’ve taken up the opportunity to do an Honours research project with the uni to test how well various wicking bed designs actually work.
The project will continue through next year so I won’t have any definitive results for a while but I’ll post progress reports here from time to time to describe what I’m finding. If you’re really interested, you can read the details of what I’m going to do in my research proposal.