Building a Raised Wicking Bed

Raised wicking bed | she cooks, she gardens

As the weather warms up that inescapable itch to get out into my garden has well and truly set in. With glorious weather in Adelaide over the long weekend we got to work on the bed I have been planning for the front garden that will be home to this years tomato crop. As outlined in my previous spring gardening post, I am keen to experiment with the construction of a wicking bed to make watering less of a hassle. A wicking bed is effectively a big self-watering pot, with a reservoir built-in underneath the bed that delivers water to the root zone via absorption or  ‘wicking’:

A wicking bed is an excellent technique for growing things in environments where water is scarce. It has 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. – Milkwood Permaculture

Wicking beds water plants from below rather than above. This works by filtering moisture through a network of absorption tanks and drainage sand to take water directly to the roots – where it’s needed most. Wicking beds work like a big sand sponge as water moves from the bottom to the top and then wets the soil that the vegies are growing in. – Costa’s garden odyssey

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. – Rob Avis

I first came across the idea of a wicking bed on Costa’s Garden Odyssey a couple of years ago and have been reading about them more and more on gardening websites. I decided it was something I wanted to have a go at myself as access to water in the front yard is difficult and involves carting water around. I came across this tutorial over on the Milkwood Permaculture website and we followed it in kind for our own front garden.

 

Wicking Bed Construction

Constructing the bed was relatively straightforward. We purchased a pre-fabricated bed from the local hardware store and filled it with gravel and Jeffries vegie bed soil from the local landscaping supply yard.

Supplies needed:

– Vegie bed – pre-fabricated or supplies to build your own. We bought a pre-fab bed from the hardware store – 1900 x 650mm.

– Gravel – enough to fill the bottom reservoir. We needed about 200 litres.

– Pond liner or builders plastic – enough to cover the bottom of the bed, plus a bit more. We put down a double layer of this plastic.

– Old bricks or something to rest pipe on in the reservoir.

– Vegie bed soil – we needed about 400 litres and bought in bulk from a landscaping supply yard. Alternatively you could try making a ‘soil lasagna‘, this is more costly than buying pre-made soil in bulk though.

– 2 pieces of PVC pipe – one the length of the bed, another the height of the bed plus a bit more. We bought a length and had it cut at the hardware store.

– A cap for the end of the pipe and an ‘elbow’ to join the two pieces of pipe together.

optional – some tutorials I’ve read added a layer of shade-cloth or ‘geo-fabric’ between the gravel reservoir and soil.

– gardening tools.

– sugar cane mulch and plants.

Instructions for constructing a wicking bed:

  1. Select a suitable site. Most vegies need at least 6 hours of sunlight a day.
  2. Clear an appropriate space slightly larger than your bed and dig down at least 25-30cm, this will be the reservoir.
  3. Lay down a length of pond liner or builders plastic to cover the bottom and sides of the reservoir.
  4. Cut drainage holes in the longer section of pipe, we started out drilling holes but then decided to cut slits using the hacksaw which had the same effect. (not pictured but example here)
  5. Attach the cap to one end of the pipe, the elbow to the other and then attach the second length of pipe creating an ‘l’ shape.
  6. Position the pipe along the bottom of the plastic, holes facing down, second length facing up. Lift the pipe slightly off the floor using some large stones, brick off cuts or polystyrene to allow the water to flow freely into the reservoir.
  7. Fill the hole with gravel, ensuring the pipe is completely covered.
  8. Level off the gravel, ensuring that the surface is level.
  9. If you are using shade-cloth/geo-fabric you would add it at this point.
  10. Move the vegie bed into place on top of the reservoir, leaving a small gap between the bed and reservoir for overflow. You could also drill a hole in the side of the bed and add a small pipe.
  11. Fill the reservoir with water, checking to make sure you have an adequate overflow (otherwise you risk flooding the bed).
  12. Fill the bed with soil and water in well.
  13. Mulch well and allow to settle for a few days before planting out.

I’ve planted out some Marigolds and Chives to start with and Tomatoes will go in later.

All up this bed cost about $170 to construct. I will start off watering on top of the bed but taper that off after a couple of weeks to allow the wicking process to take over. Then it will be a matter of refilling the reservoir as needed. I popped a piece of leftover plastic over the top of the exposed pipe to stop leaves, mosquito larvae and other undesirables getting into the reservoir.

Step by step pictures below, click the photo to bring up a slide show.

So what do you think? Would you like to give this a go in your yard?

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