Wicking Bed Construction – Step by Step
In this instructional article we’ll be using a galvanised steel raised bed as the base for our wicking bed.
Also, for ease of construction, we’ll use a slightly simpler design where the water inlet tube is just a straight pipe with no bend in it, as shown in the diagram below:
- Place or construct the raised bed in the desired location, once it is filled with soil it will be immovable!
- Ensure that it is level by using a spirit level – place the spirit level crossways and lengthways and at various angles to determine if it is level.The wicking bed needs to be level because it will hold water at a specific height, if it is angled it will drain out one side and be too dry on the higher side or not drain properly and be wetter on the lower side.If a side of the bed is low and needs raising, lift the bed slightly and pack more soil underneath to elevate it, if it is high, dig some soil out.
If you’re wondering about the four white tubes inside the top edge of the raised bed, they are part of it, it’s purchased that way. The vertical tubes are used for attaching flexible pipe from one side of the bed to the other to make a half-circle tunnel -shaped frame to support a covering material such as bird or insect netting. shade-cloth or plastic.
3. Drill hole in the side of the raised bed, 20cm (8”) above the ground
4. Lay down the pond liner inside the raised garden bed and check that it fits properly.
5. Install the 20mm threaded pipe outlet (bulkhead connector). Cut a hole in the pond liner just big enough to fit it through the hole, no larger, and ensure that the rubber washer of the fitting is against the pond liner to ensure a watertight seal.
6. Prepare the water inlet pipes – if using the vertical modified design, drill 10mm (3/8”) holes all around the last 30cm (12”) of the 50mm (2”) wide PVC pipe, length should extend high enough above raised bed to allow efficient watering without reaching too high or pushing plants out of the way to find the watering inlet.
If using the more common design of an “L” shaped water inlet, use two lengths of pipe and an elbow join. The horizontal section should be approximately half to three quarters the length of the bed, and should be drilled all around and over its length with holes approximately 10mm-12mm (3/8”-1/2”). Join the two pipes with the elbow join, just push-fit the pieces together, a friction-fit is sufficient.
7. Lay down a thin layer of coarse scoria over the pond liner. This will bed it down and put a protective layer of scoria over the pond liner so that it can’t be damaged by the PVC inlet pipe.
Important – This modified design used only one shorter piece of inlet pipe and no elbow joint for the pipe, it is ‘I” shaped and not “L” shaped as in the previous design, so the cut end of the pipe is pointing straight down onto the pond liner, make sure there is an adequate layer (5cm or 2”) of gently packed-down scoria between the end of the pipe and the pond liner to avoid puncturing it if the pipe is pushed down!
8. Clamp the pond liner to the top edges of the garden bed right around using small spring or screw clamps to keep the pond liner in place while the bed is filled with materials.
9. Fill the garden bed with coarse scoria to the height that is level with the overflow outlet. Make sure that the scoria layer is fairly level and even.
10. Lay down geotextile fabric (or shade cloth) over the scoria layer.
11. Wrap well around inlet pipe, allow the fabric to come up around the pipe to prevent any soil entering the scoria layer.
12. Cover the scoria layer with two layers of geotextile fabric (or a single layer of dense shade cloth) and extend it up around the sides of the pond liner by at least 15cm (6”).
The geotextile fabric can be tucked in all around where it makes a corner with the sides to secure it in place, just push the bottom part or the vertically extending sections between the pond liner and scoria. This is to make sure that no soil can get into the scoria layer.
13. Check that the scoria layer is level. If there are any high spots, pat them down. Low spots can be raised by pressing around the sides of the low area to push scoria into the area to fill it.
If the scoria is far too uneven, lift a section of the geotextile fabric, level the scoria layer, and then put the geotextile fabric back in place.
14. Check once more that the scoria layer is level under the geotextile fabric.
15. Begin filling the raised bed with the soil (50% soil, 25% compost, 25% cow manure mix or your own blend), ensuring that the pond liner is kept against the walls of the raised bed as you fill with soil.
The blue plastic pot at the top of the water inlet is there as a cap to prevent dirt and other objects entering the water reservoir.
16. Trim off excess pond liner with scissors leaving about about 3cm (1-1/4”) of pond liner the soil line.
17. Wicking bed completed and ready to plant and water!
To get the system to wick properly, you need to evenly wet all the soil first by gently watering the soil from above repeatedly until water starts running into the scoria layer.
Once the soil is evenly wet, fill the water reservoir through the inlet pipe until water begins to flow out of the overflow pipe.
Plants up the wicking bed and mulch your plants to conserve moisture, then sit back and relax!
Getting More Out of Your Wicking Bed
Mulch – The reason why there is a considerable lip or edge above the soil level , around 10cm (4”), is to allow the bed to hold a nice thick layer of mulch above the soil. Mulch keeps the moisture in the soil, prevents evaporation, and conserves water, and the purpose of building a wicking bed in the first place was to reduce watering. If you’re building your wicking bed in the warm seasons, always mulch!
Mulch with a layer of mulch around 5-7cm (2”-3”) so the water lasts longer, and your plants roots stay cool. The mulch will also break down slowly and add nutrients to the soil. For mulch material in a vegetable garden bed, you can use pea straw, lucerne, hay or sugar cane mulch.
In-soil worm farms – you can also construct worm farms directly in the wicking bed using worm tunnels (see article Build a Worm Tunnel Vermicomposting System) so that the whole wicking bed becomes a wicking worm farm, that way the earthworms generate worm castings, one of the best known fertilizers, within the garden bed itself!
Water recycling – the water that flows out of the water overflow outlet will be loaded with fertiliser so you can run that water into a bog garden, reed bed system or a garden bed in the ground for moisture loving plants (if you get enough water overflowing!)
Extra growing space – wicking beds, like other raised beds, can support frames or trellises to grow climbing plants on such as beans, peas, cucumbers, watermelon and any other edible annual climber you fancy. Keep in mind that you cant hammer stakes or poles into the wicking bed itself, that will punctuate the pond liner and destroy the watering system. The frame, trellis or support has to either be anchored into the ground or attached to a wall behind the wicking bed.
Protective covers – as with other raised beds, you can make a frame to support bird netting or insect exclusion netting to protect the plants in your wicking bed from pests. Another possibility is to use clear greenhouse plastic to make a cloche tunnel for extended season growing.
Wicking Bed Maintenance
To maintain a wicking bed, flush out the whole system at least once a year. If the wicking bed is undercover and not exposed to rain, which helps flush it out naturally, consider carrying out the task perhaps twice a year.
To clear away high levels of salts that are building up at the top layers of the soil, water from above to wash them out into the water reservoir and out of the outlet pipe.
Also, remember to go easy on the fertiliser when feeding the garden bed in spring and autumn, as fertiliser levels can accumulate in wicking beds because every bit of fertiliser that you put in stay in the system unless it is washed out.
Other than that, maintain a wicking bed just like any other raised bed. Source.