Tree roots are a constant challenge for inner-city vegetable gardeners, particularly when they’re from camphor laurel trees. Over the years, I’ve taken various steps to protect the beds, including replacing some of the existing raised beds with entirely enclosed tanks. Because of the cost and effort, I only re-engineered the lower beds that were closer to the trees, hoping that this would be enough.
Sadly this was not the case. My top bed, closest to the road, had been steadily dropping in productivity, so I had a poke around. And sure enough, the bed was filled with tree roots, coming up from underneath.
So I decided to rework this as a wicking bed. Deep Green Permaculture has by far the best description of how wicking beds work, including a description of both advantages and disadvantages (something I haven’t seen anyone else cover).
The starting point was to dig out all the soil from the bed, tacking it down to a flat surface free of rocks or other sharp objects.
And this is just a fraction of the roots that I dug out of the bed, which wound themselves around the entire perimeter of the bed, reaching almost up to surface level. No wonder the bed was struggling!
The bed is lined with pond liner, which I obtained from Clark Rubber. (I noted that some instructions suggested using much cheaper builders plastic, but the Deep Green Permaculture notes strongly discourage this, as the thinner plastic just doesn’t last.)
A thin layer of scoria (rough volcanic rock) then goes down underneath the ag-pipe. (I obtained the scoria from BC Sands, and had it delivered in a 1-tonne bag.)
A 20cm deep layer of scoria was then laid down, covered by a layer of geo-textile. I also drilled an overflow valve at the top of the scoria, with a tank outlet screwed in.
I then re-filled the garden bed, adding a lot of home-made compost, fertiliser and trace elements.
All up, about a day’s labour was required, but the new bed is now back to being highly productive. I have enough left-over scoria to do another bed, which I’ll do when the season ends.