wicking beds

How to construct garden Wicking Worm Beds

"The wicking worm bed is a highly productive growing system which not only produces more food from limited water, but also recycles waste organic material to provide plant nutrient and capture carbon. The essence is to form an underground reservoir of water or pond contained by a waterproof container or liner below the surface of the soil. Plants are productive because they have a continuous supply of water and nutrients." Colin Austin

Water once a week in summer and less during the rest of the year!

Water doesn't evaporate in the reservoir under wicking beds.
Instead, the water 'wicks' up to the roots, and the top soil will remain soft under the mulch.

Since water will wick up only 300mm to the plant roots, the soil depth should be no more than 320mm deep (about one foot deep).

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This booklet provides detailed information, including exact measurements and lists of materials needed for constructing timber-framed Wicking Worm Beds, plus everything you need to know about adding compost worms to the wicking beds.

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We built our first wicking beds in 2009, using a combination of suggested methods, as follows:
Wicking Beds
Step 1.
We removed the soil from our existing 5x3 meter garden bed and then leveled and terraced the ground for the two new beds, which must be completely level for even water distribution. We put a layer of soft-sifted soil on the bottom for cushioning —to protect the plastic from sharp objects (you can use sand instead), and created a waterproof bed with the 200um plastic sheeting.
Make sure no sharp objects can cut into the plastic sheeting
wicking bed1

wicking bed2

Step 2.
We added the agi-pipe, stretching
the full length of the bed.

Step 3.
We covered the bottom of the bed to just above the pipe with the screening rocks.

Make sure you have enough space left for soil plus mulch: 330mm (about 1.08ft)

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wicking bed3
wicking bed6

Step 4.
We lowered the PVC pipe to the bottom of the bed, and positioned it in the 'mouth' of the agi-pipe, then we covered the rocks with the shade cloth, to separate the soil from the rocks and pipe. We then drilled a drainage hole at the opposite end of the bed, at the level of the screening cloth - or 330mm from the top of the bed.

NOTE: The water will wick up no more than 300mm through the soil, so the soil level should be 300mm above the water line.

Step 5.
Then we sifted the old garden soil into the bed, removing stones, seeds, weeds, and roots. (The above photo was taken from inside the house).
This was backbreaking, tedious work --bending, and reaching out with a heavy tray of soil, then shaking it to sift it out, so we decided to put new soil in the second bed. Easy!
wicking bed5

Step 6.
We did it!
We sifted the old garden soil, used a pH soil test kit (around $15.) and worth having) then added a generous mixture of our own organic compost, mushroom compost, lime, and blood & bone, --leaving a space at the top for mulch.

Alkaline pH 7 soil is perfect for above ground veggies. Most root veggies like a slightly acid pH soil, round 5.5 - 6.5 pH.

wicking bed6c
wicking bed8

Step 7.
We filled the top with a layer of organic sugarcane mulch, and drilled the drainage holes. When it was finished, we added the water through the pvc pipe - testing how long it took to fill the bed to the drainage hole, and measured the water level in the pvc pipe, so we can know in future, by looking into the pvc pipe, when the water is low.

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Step 8.
Next, after a couple of days break, (to heal our sore bodies and attend to work in the studio) we built the second (terraced) bed on top of the old garden bed soil, (no more digging for us! :) We use the remaining screening rocks to make a gravel pathway between the beds. We waited until the waxing moon to plant above ground winter veggies, using a combination of seedlings started in our glass house, below, and from the local nursery.

(We later cut the pvc pipe down to the level of the beds, and put wire screens on top, to keep snales out, while allowing for ventilation.)

wicking bed9

We still grow vegetables in the in-ground beds on the western side of the garden, next to the (8x10 ft) Eden Glasshouse, which we saved from demolition by my mother's new neighbour. We saved a third of the internal space for sitting.
This is a fantastic place to escape to in the middle of a sunny winter day - cold outside and so warm inside.

In this patch, we currently have winter root veggies slowly coming up, -- garlic, radishes, beetroot, carrots, onions, spring onions, with various lettuces, spinach, bok choy, and herbs out of view.

glasshouse collage

Email message from Colin Austin, the inventer of Wicking Beds, June 2009 (I've highlighted the essential information in red.)

Hi Maireid,

Well we have great debates here on this issue of the best depth for the water and soil. Peter (of easygrowvegetables.com) and
my neighbour and I spend many hours over a bottle of red wine arguing this point. If you do not like my answer
write to Peter (pva36152@bigpond.net.au) and you will get a different view.

What we do agree on is that water will only wick up some 300 mm. In my early experiments, I had my holes much higher than Peter
but I watered until it reaches the holes then I don't water again until all the water has gone. This means that the roots are only in
saturated water for a short time. This seems to work fine if the beds are not regularly flooded by rain. We may get a couple of
weeks when it rains every day and submersing the roots for that length of time is definitely not good.

Peter had his holes much lower to avoid getting the roots saturated.

Now we are making our beds deeper with about 300mm of soil above the high water line. Using the shade cloth, this avoids any
problem with water logging.

What we are debating now is how deep we can make the water reservoir. Out last lot of beds were 500mm overall giving
200mm for the water reservoir
and 300mm for the soil bed. This is working fine.

I think that we could make the water reservoir a little deeper still. This cuts down the time between watering. On the latest bed
I tried 300m and 300mm. Before, when we had to dig the trench, making it deeper was hard work. Now that we're using raised beds
digging is not so much of a problem. Because I am old the last bed I made I dug out all the top soil (about 300mm) then made
the raised bed a further 300mm which was quite quick to make.

I have only just put the seeds in so do not know how it will work but I am optimistic.
You can see picture on my other web site www.wickingbed.com

I will let you know how it goes.

Sorry, there is not a simple answer. It also depends on what you are growing. I guess if you are after a rule of thumb make the
soil layer equal to the natural root depth of the plant
(for veggies about 300mm) and then decide the depth of the reservoir
on how long you want between irrigations, but you will be lucky to get any benefit above 300mm.

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