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Science of wicking beds

This information is shared to the wider community in the hope that it will help more people to grow more food.

If you have ideas for further research, we hope you will share your research findings too.

Why research wicking beds?

31/5/2019

6 Comments

 
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.
6 Comments
zazu
9/3/2020 04:39:28 am

thats one interesting project
if i'm not wrong, you're chris who rob posted one of your videos experimenting with sand vs gravel right?
i found a paper by Niranjani et al 2016
that evaluated the efficiency of the wicking bed compared to precision irrigation
but no research ever done on inground wicking bed
a design that use sand as medium will be a very simple and cost effective design for inground beds
i once did read alot about soil water retention and for loose compacted uniform sand the pore space is around 25-30% of the volume
but if the sand contain lot of silt, that pore space will go down
so sand should be washed from silt
i'm planning to make a wicking bed with compacted clay+sand mix as impermeable substrat and washed local sand as medium

Reply
GLO
8/7/2020 12:19:54 am

Thanks for sharing this. In your article you mention:

'I filled the hollow legs of the WaterUps with coarse perlite and have subsequently found that this does not wick as well as perlite with smaller particles.'

Can you also conduct the clear perspex tube experiment with the various grades of Perlite? Ie super coarse, coarse, regular. I would love to see the wicking ability / capillary action of the different grades of perlite in that test environment.

Thanks in advance.

Reply
Chris Curtis
8/7/2020 10:10:54 am

I replaced the perlite in the legs of the waterups with sand for my second round of experiments. I think that wicked better than the perlite and resulted in very consistent moisture in the soil in these beds. I'll add some more capillary tests with different grades of perlite to my todo list :)

Reply
Chris
29/11/2020 07:15:28 pm

Wow, I'm really glad that somebody is actually scientifically researching the use and effectiveness of wicking beds.

I'm currently trying out wicking beds myself though unfortunately through a hit-or-miss method (which my reasoning-based nature makes me so not fond of, haha).

I really look forward to your results! =) Thank you for sharing this. Keep well.

Chris, Malta (Europe)

Reply
Otto Flowers
22/2/2021 02:49:50 am

I am considering cutting the top 7 inches of a 5 gallon bucket off to allow me to fill it with sand, then fill the rectangular lidded reservoir with water with a hole cut for the contained sand and place the cloth grow bag on the surface of the sand. It should wick up throughout the bag.

Reply
Chris
22/2/2021 12:04:45 pm

That sounds like it should work well as long as the grow bag will allow the water to pass through it. I have found that a sand column surrounded by free water wicks very well.

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    Chris is exploring how wicking beds work for a Charles Sturt University honours project. This blog reports on the findings of this original research.

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