From the Bottom Up – A DIY Guide to Wicking Beds

by Rob Avis

Wicking beds are a unique and increasingly popular way to grow vegetables. They are self-contained raised beds with built-in reservoirs that supply water from the bottom up – changing how, and how much, you water your beds. In this article, we’ll talk about how wicking beds work and why we love them. We’ll also show you some great examples and leave you with ideas and instructions for creating your own.

How Wicking Beds Work

A wick works through capillary action – the same force you observe when you dip a piece of tissue paper partially into a glass of water and watch the water climb the paper. Wicking occurs in many materials; cotton, wool, geo-textile, soil, gravel and even wood to some degree. Every material has different wicking properties which you can test by placing that material into a glass of water and watching the water “climb” up. When one end of the wick is saturated and the other end is dry, it creates a moisture gradient, which drives the wick until the gradient no longer exists or you run out of water. With the earth box, one of the more popular examples in North America, the soil is suspended above the reservoir with wicks dangling into the reservoir pulling up moisture. As the plants use the moisture in the soil, it creates a moisture gradient (the soil is drier than the reservoir) which drives moister through the wick into the soil.

Advantages of Wicking Beds

Wicking beds have a lot of advantages over standard raised beds and in-grown swale-based gardens:

  • They are water-efficient! Watering from the bottom up prevents evaporation of surface water (which occurs when you water beds from the top).
  • They are self-watering! Wicking beds are an especially great system to use in community gardens because they save people from driving every day during hot weeks to water their beds. A full wicking bed should irrigate itself for about a week.
  • They can be placed close to the house without risk of flooding your basement, since the water is contained in the bed. This makes wicking beds a great alternative to swales on properties with sump pumps or basement water issues.
  • No evaporation means no salting of soil. If you are watering your soils from the top with hard water, you risk accumulating salts, because the water evaporates and leaves the minerals behind. Eventually your soil will struggle to support plant life.
  • They provide a lot of drainage in the event of a large downpour.
  • Since they’re raised, they will warm up quicker in the spring.
  • You can easily attach cold frames to them.
  • They are great for people with less mobility and strength as you don’t have to haul heavy water containers.
  • By using an intermediary tank, you can automate the watering process… but more on that in a future blog.

Disadvantages of Wicking Beds

Wicking beds do have some disadvantages as well:

  • They cost more to install than in-ground swales and standard raised beds.
  • They will freeze sooner in the fall than non-raised beds.
  • There are additional freeze/thaw considerations that need to be taken into account, which is not required for conventional gardens.

Types of Wicking Beds

Reservoirs with Media

Most of the DIY sites for wicking beds focus on building beds that use media, a layer in between the soil and the water reservoir, as their wick. This is an easy and cheap way of supporting the soil on top of the reservoir. Gravel is the most common medium, but there are a number of materials that do the trick. Here’s a good DIY blog on media wicking beds.

Media-less beds

Beds without media require a false bottom that will allow the soil to be suspended above the water reservoir. Again, this wick system can be made from a variety of materials. Here are some examples of media-less wicking beds:

And a video example….