How does wicking work?
Wicking is the movement of water by 'capillary action', where water from a reservoir below the soil is drawn up and evenly distributed through the soil to the plants' roots. Excess water goes through an overflow pipe, which ensures the soil doesn't flood and doesn't drown the roots.
Advantages of wicking garden beds
- As water comes from below, there's no surface water loss via evaporation.
- Watering from above can cause fungal damage to foliage.
- Roots that need the water get it, not the top bits.
- A constant water supply means stronger, healthier roots – think of plump, tasty carrots and beetroot.
- As the plant is always fully hydrated, leaves don't get sunburnt during heat waves.
How to build a wicking garden bed
Gather your supplies
- Raised garden bed with base (Adam used this one from Kingspan.)
- PVC pond liner
- Slotted agricultural pipe with end coupling and cap
- Overflow tap, male and female parts
- Silicone sealant
- Geotextile fabric
- Potting mix
- Vegie seedlings
- Sugar cane mulch
You'll also need
Here's how to make a wicking bed
Position your raised garden bed in full sun and on a level surface.
Line bed with pond liner, ensuring there are no holes or gaps along edges and corners. Hold in position with bulldog clips.
Add 25mm of scoria to base of the bed.
Coil agricultural (ag) pipe around scoria bed, with cap end sitting on rim of garden bed. Cover pipe with more scoria
Drill 20mm hole into side of garden bed, just above scoria.
Install overflow tap parts in drilled hole and seal with silicone sealant.
Trim liner to just above scoria.
Cover scoria with geotextile fabric. Cut opening for ag pipe and trim fabric to fit.
Fill garden bed with quality potting mix.
Plant seedlings, cover mix with sugar cane mulch and water well.
After a couple of weeks when roots are established, fill pipe with water. Put cap on to prevent mosquitoes breeding.
What are the disadvantages of a wicking bed?
If you let the overflow water drain into the ground, you’re wasting water. If you let the overflow water drain into a bucket, empty it immediately into other parts of your garden or you’ll attract mosquitoes.
What do you fill a wicking bed with?
Line the base of a raised garden bed with pool liner then fill with scoria or pebbles – not road base as there is too much fine material in it – into which you place an ag pipe, cover with geotextile fabric then fill with quality potting mix. The ag pipe protrudes through the potting mix as that’s where you add the water for the underground reservoir.
How deep do wicking beds need to be?
As deep as you like, but the soil/potting mix should be about 30cm deep.
What is the best soil for wicking beds in Australia?
Only use quality potting mix. Soil needs microbial activity such as worms, beetles and beneficial organisms such as fungi and bacteria to keep it aerated. Without this underground activity the soil collapses and nothing will grow there. Potting mix needs to replaced every couple of years as it breaks down and collapses too. You can toss old potting mix onto garden beds where it breaks down further.
Top 6 raised garden beds
For more great gardening stories, check out the latest issue of Better Homes and Gardens magazine.
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