A few thoughts on wicking beds
One of the big hits at Permablitzes are wicking beds. It is time that we talk a little bit about how they work, why they work, and what you can do to make them better. First let’s take a look at the physics behind water movement in soil and plants to better understand what the magic behind wicking beds actually is.
How plants use water
Plants have leaves. Leaves are like big evaporation pans cum solar panels. They make energy and they evaporate water. When the water leaves the leaf to go into the atmosphere, water gets pulled up out of the ground in the roots. Imagine a well with a rope and bucket on the bottom. As you pull from the top, the water comes up. The powering force behind this well is called ‘water potential’. At the lower end of plants are the roots. Water moves into the roots from the surrounding soil through osmosis. That is a process you might remember from school where water moves to a location of higher mineral concentration (water wants to dilute stronger solutions) through a semi-permeable membrane. You can read more about this here on nature.
That water is now missing in the soil around the roots. This is where wicking comes in. Because soil particles sit very closely together, capillary forces move water into the space that is void and fill it with water. Wicking doesn’t work where the spaces between the soil particles (such as rocks) are really big.
The problem with loving your plants too much
If you understand the process above it becomes clear that the solution (water) in the soil surrounding the plant shall not be stronger than the solution inside the plant (sap), because otherwise the osmosis that gets the water into the plant in the first place, gets reversed and water flows out of the plant into the soil and dries up the plant. Result: dead plant. Not cool.
With a normal garden bed, over-fertilization is rarely a problem, because the excess nutrients will get flushed out by the rain or watering and end up in the rivers and then in the oceans. Ever heard of “dead zones” in oceans or algae blooms ? That is where these come from: over-fertilization.
Everybody loves their plants a lot and so people tend to apply lots of water and fertilizer. Especially with wicking beds, that could be a problem. In a conventional garden bed, when your plants looks a bit unhealthy, you water more and the nutrients get flushed out, your plant recovers. However in a wicking bed the nutrients are there to stay, because the base is lined.
Why wicking beds stink (but they don’t have to!)
So when there are too many nutrients in the wicking bed, bacteria start to use the delicious nutrition and ferment them into greenhouse gas methane and other even less palatable compounds that tend to smell quite unpleasant. And if you apply extra water, it doesn’t work, because it just accumulates in the reservoir.
So here is what you can do to help your wicking bed:
- Don’t over-fertilize!
Most books tell you to fertilize every two weeks in summer, don’t do that with wicking beds.
- Make roots grow into the reservoir!
Don’t use rocks, sand and cloth in wicking beds, they are contrary to what is going on in nature. Just line the bottom half way up the container, put in a slotted standpipe to check water level and fill with soil. That way, the plants can grow roots well into the reservoir and suck it out.
Note: This point is by far going to be the most controversial, as it goes against everything we’ve known and taught thus far on wicking beds. For the record, Permablitz has always used the plastic liner, overflow/aggi-pipe/screening/geo-textile fabric or shadecloth/soil approach – and the results really do speak for themselves.
The point above suggests that the use of cloth will prevent roots from reaching the reservoir – anyone who has had to disassemble a wicking bed after 12 months or so will know that roots definitely do reach the reservoir (depending on the plant of course)!
This is not a criticism of the point, as it has indeed come from the original inventor of the wicking bed – this simply reflects his updated approach to working with wicking beds.
- Water from the bottom
Don’t apply water as you would normally in a garden bed. Only put water into your standpipe and fill the reservoir from the bottom.
- Use seedlings
There are many benefits to using direct seeding but in wicking beds you can’t water from the top, so seeds would dry out and don’t germinate. So with wicking beds it’s better to use seedlings (you can raise them yourself in trays of course).
I hope by following all these tips, your wicking beds should work beautifully and smell amazing. Let us know how you go!
I got inspired to write this article by the deliberations of Colin Austin, the inventor of the wicking bed. Check out his website and make sure to sign up for his newsletter.