How to Make a Wicking Bed
May 11, 2010 | Community Projects, Courses + Workshops, Gardening, Off-Farm goings on | 72 comments
| Author: Kirsten Bradley
A wicking bed is an excellent technique for growing things in environments where water is scarce. It’s got two main parts: the bottom half is a contained reservoir filled with gravel and water and the top half is filled with soil, mulch and plants. By periodic flooding of the deeper half of the bed, mature plant roots get a big drink. And because it’s contained, that water gets a chance to ‘wick’ upwards into the soil, hydrating the soil of the bed and the smaller roots within.
Pretty simple, really, but amazingly effective, very water efficient and ripe for endless variation.
Below is a photo essay outlining the process of creating a wicking bed using everyday tools and materials, which took 5 people about 4 leisurely hours to make. It features the efforts of our awesome PDC
students in Alice Springs earlier this year, led by Nick Ritar who also designed this particular wicking bed system..
The first step is to create the reservoir which will hold the gravel and the water. This bed shape and size is based on the footprint of a watertank, a strip of which we’d found to use for the sides of the bed. Make the reservoir around 30cm deep, regardless of the size or shape of your bed.
To make a ‘closed wicking bed’ like this one, you want the reservoir to retain its water for as long as possible. We used builders plastic to line the reservoir.
Here is the water pipe that will deliver the water to the reservoir. The line of holes will be positioned facing the bottom, so that plant roots do not enter the pipe.
The water pipe sits on three chocks to create a space between the holes and the ground, so the water can get out of the pipe and fill the reservoir. A vertical section will be added to the water pipe via the elbow at bottom left. The pipe is closed at the other end.
The reservoir is now filled up with gravel, covering the water pipe’s horizontal section. The gravel in a wicking bed reservoir is there to provide a structure for the soil to sit on top of while coming into contact with the water below.
The next step is to put the walls for the raised part of the bed on top of the reservoir. Where the reservoir ends and the bed begins, it is crucial to have an overflow. This means that, if the reservoir over-fills, the water has an escape point before it waterlogs the soil of the bed (and kills all the plants within).
In our design we created a simple overflow by raising the iron for the bed surround on pieces of clay pipe, which created a gap of about 3cm between the plastic and the bed surround above. The gravel was then raked over this gap so that soil will not escape in the event of overflow.
Now, if the reservoir over-fills, the surplus water will seep out of the bed at this overflow point and into the surrounding garden, saving the plants in our wicking bed.
And now for some soil, to a depth of about 30cm. You can see the hose going into the vertical section of the waterpipe (with a paver on top of it), filling up the reservoir for the first time. The plastic surrounding the bed will be covered with gravel and provide a weed-free barrier around the bed which doubles as a path. And also won’t turn into a muddy swamp when the bed overflows.
And for a passive fertiliser system – an in-garden worm farm! The worm juice and castings from this small system will leach out into the bed through the holes in the bottom of this box, fertilising the plants. A small proportion of worm juice may make its way down to the reservoir and mix with the water, further enhancing the biological relationships that will keep this bed’s soil humming.
A small but important task to make this bed serviceable – making a top rim out of old hosepipe which fits over the sharp edge of the corrugated iron that the bed surround is made from. Otherwise planting and harvesting in this bed could be a painful business.
Topsoil all in, a heavy mulch of pea straw is applied to keep the moisture in the soil where we want it. The small square in the bed is the lid of the waterpipe, and the larger rectangle is the lid of the in-garden worm box.
The inlet of the waterpipe serves two functions – firstly, you can fill the reservoir of your wicking bed – by bucket, hose or other water source. Secondly, this inlet hole allows you to see the level of water in the reservoir below, and so to accurately gauge whether your wicking bed needs more water added. A lid is a good idea to prevent evaporation and to keep your waterpipe clear of leaves, mosquito larvae and any other visitors you might not want in your system.
And there you have it – one completed wicking bed (with in-garden wormfarm)! The bed is now ready for planting a bunch of water-loving vegies which would be otherwise hard to grow in the dry climate that is Alice Springs. The property owner has promised us photos in due course on how the wicking bed vegies go, so we shall report back. But isn’t it a brilliant system? We ‘re in love with its efficiency and simplicity. Thanks, team!