Wicking bed trouble shooting

Sophie Thompson shown in the media next to her Adelaide Hills garden

I admit I am addicted to building wicking beds.  I really do love them and if I could start my vegie garden over again, I would probably make the whole thing from wicking beds.  I think they are the perfect way to grow vegies in our hot, summer dry climate as the vegies take the water they need, when they need it and they save so much time in watering – the perfect solution for busy people.

However, over the years I have had to remake two of them when they leaked and didn’t hold water.  I have also had a number of people contact me when their wicking beds were not working, for a variety of other reasons and so here are the main problems I have encountered.

Problem: The wicking bed leaks or doesn’t hold water.

Possible cause: Punctured liner.  The first time I had to remake a wicking bed was because I punctured the black plastic liner by sticking a tomato stake into the bed.  I know this should have been obvious but …  At this stage, I was making wicking beds from any container lined with builders’ plastic (see this this ABC Gardening story) and I had six beds at the time.  While the others could go a week before they ran out of water, this one would only go a half a week as I had punctured the liner halfway down the reservoir layer.

Possible cause: Pressure release on lid.  This last one, which I had to remake, was actually one we built from an Intermediate Bulk Container (see this ABC Gardening story).  It never seemed to work properly and I would fill it with water to the point where the overflow pipe was working, but the next day it always had drained out again.  We worked out that it was the top half of the IBC container and had the screw-top lid on it.  This particular type of lid had a pressure release valve which would slowly allow the water to leak out, so the only way to fix it was to dig everything out, seal the value with silicone and make the bed up again.

Solution and prevention: Always fill the bed and check for leaks before you add the geotextile fabric and soil.

Note: Some beds do go through water more than others because their crops will be using different amounts of water, so use common senses to judge if there is a problem with your bed or whether you just have some very large thirsty crops growing.

Problem: Wrong material in the reservoir layer.

Several years ago I made a wicking bed which nothing would live in and I couldn’t work out why till I remembered I had not used scoria to fill the reservoir layer.  When I was making it I used blue metal which was lying around the property.  I had not thought through the fact that blue metal is very alkaline and it took several years for this to leach out and me to be able to grow crops in the soil.  For the same reason, I would not use crushed limestone as it is also very alkaline and will cause your plants to struggle.

Problem: New seedlings dying.

Possible cause: Dried out.

When you first make your bed it is really important that you thoroughly wet the soil before you plant.  Also when you plant new seedlings you still need to water them in from above and water them every day or two for a few weeks until their roots are strong enough to start the wicking process.

Possible cause: Poor soil with not enough organic matter in it.

Wicking only works when the soil is high in organic matter.  How much organic matter is enough?  Well, that is a bit tricky to cover with a general statement but it should look dark and look and feel like good vegie garden soil when you touch it.  Generally, I use good quality commercial vegie garden soil and then add about 1/3 to 1/2 more compost to it.  Then, every time I harvest one crop and remove it, I add more compost.  Personally, I don’t use mushroom compost as it can be very alkaline and cause yellowing and failure to thrive.  Like all vegie garden soil, the soil in the wicking beds is like a brew, which takes a while to get right.  If you are feeling uncertain, do a pH test and aim for soil in the 6.5-7.5 range.

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