Wicking Beds

Diagram from the Permaculture Institute of Australia.

If you garden in raised beds you've probably spent a lot of time watering and this year probably even more than most. Raised beds offer the gardener a myriad of advantages but being water wise is not among them. So what is the water conscious square foot garden devotee to do? One solution is wicking beds. Wicking beds take advantage of soil's ability to wick water up through capillary action. The same process that occurs when you stick the end of a kleenex or paper towel in water. In a wicking bed there is a water reservoir underneath but in contact with your soil or potting mix which, by filling, allows you to water your garden from below.

A popular example of a wicking bed system is the Earth Box, but there are many DIY examples and no reason to limit yourself only to containers. At the Downtown Farmers Garden we decided to test one out and replaced a traditional raised bed with a wicking system. The specifications for constructing a wicking bed vary with the one universal being that water can only wick effectively up to one foot. The design we settled on starts with a one foot deep hole that is four by eight feet wide. We placed a 4x8 piece of treated plywood at the bottom to act as a root barrier. Such a substantial root barrier is only necessary if the bed is located close to trees which ours is. We then laid in the two foot tall frame taking care to keep everything as level as possible.

Pond liners were a bit pricey so we decided on 6 mil construction plastic sheeting which we doubled layer in case of punctures.

A six inch layer of gravel, or stones along with the watering pipe is laid down which will comprise the water reservoir. We used lava rocks. The watering pipe is placed in the middle of the six inch layer of stone.

Another layer of ground cloth is laid atop to prevent soil from entering the reservoir and the six inches of soil which will act as the wicking layer. It is above the wicking layer where drainage holes are placed to allow for excess water to escape. Because this is Florida and large amounts of rain are not uncommon we will be drilling ample drainage holes to hopefully prevent any chance of flooding.

The next layer is shade cloth or another very porous fabric to allow wicking but discourage roots from entering the wicking layer where they are likely to get drowned.

Finally, the remainder of the bed is filled with our growing medium, a mixture of the GM2 mix from Soil Enrichment Products, and some native soil we displaced digging our hole. These systems are growing in popularity, especially in arid regions, but are still new and long terms effects to the soil and their durability are not well documented. So stay tuned, as we keep growing!

And here are some links with more information on wicking beds:
http://www.sgaonline.org.au/?page_id=5533
http://permaculture.org.au/2011/06/20/from-the-bottom-up-a-diy-guide-to-wicking-beds/
http://www.theruralindependent.com/garden-projects/wicking-beds