In April 2011, I wrote about our efforts to fight off tree roots that were invading our garden beds. We took the job pretty seriously I think, digging up the beds, laying down bark, weed matting and old carpet.
It didn’t work. Oh, it went fine for a while, and we rested easy. After a year though, the bottom three garden beds became less and less productive, and we knew we’d lost when we started digging up feeder roots from the trees just under the surface of the beds.
Doh! (For those that commented on the original post, I’m not too proud to say: you were right.)
Rebuilding our garden beds
This time around, I decided to put in what I hope will be a permanent solution: garden beds with solid bases.
I ordered them to match the current beds in size and colour, but this time with a solid base (basically the bottom half of a water tanks).
We considered creating wicking garden beds, which are an elegant solution. Unfortunately they don’t really match up with our existing watering system, which is designed to provide a small amount of water frequently (via water spikes).
So we decided to create “giant self-draining pots” instead. This is how we did it…
The serious labour at the beginning of the job was to dig out the 1.5 tonnes of soil out of the bed, and to clear away the pebbles around the base. That also surfaced the source of the problems: the multiple large tree roots that had invaded the bed via a small gap in the corner.
I then cut two holes in the side of the tank with a hole saw, for drainage.
These holes were designed to accept a 25mm threaded tank outlet, as follows:
The tank outlets are above the ground level, and will ultimately sit in the pebble bed above a layer of weed matting. I’ll also be connecting the outlets to lengths of 19mm irrigation pipe, drawing the water away, and making it even harder for roots to invade the bed.
With that done, and the bed leveled and in place, the next consideration is ensuring good drainage within the garden bed.
While I could’ve used gravel, it’s heavy to use, and will tend to clog up over time. Instead, I used 30mm Atlantis Flo-Cell, which lays down as sheets across the base of the beds.
Two layers were sufficient to get above the tank outlets, and to ensure good drainage.
A small amount of gravel was used to plug the gaps, and a layer of geotextile was then laid across it all.
After filling the bed back up with soil, the result looks no different than any of the other beds. But hopefully it will be proof against roots!
Is this a lot of work? Yes, oh yes. At the end of the day, though, there’s no point in having raised beds if they’re not actually growing food.
I’ve still got two more beds to do the same way. So any suggestions on improvements or modifications welcomed!
When establishing our raised garden beds, I had thought this would proof us against issues in the soil, including the impact of neighbouring trees. How wrong we were. The camphor laurel has proven to be very vigorous, and when I turned over the soil in the bottom two beds, I found feeder roots coming up through the bottom of the bed. No wonder the plants weren’t growing properly!
No choice but to take drastic action (short of cutting down the noxious tree itself).
The starting point was to fully dig out the garden bed, which was no small task, as there’s 1.5 tonnes of soil by a previous calculation.
Having dug the bed down the level of the original gravel, I laid down a layer of bark mulch. This is something that I saw on Gardening Australia, where the nitrogen draw-down of the mulch rotting creates a low nitrogen layer. This should help to discourage or deflect the tree roots. (This is the experimental bit, I hope it works!)
Multiple overlapping sheets of weed mat should then form an impervious barrier to the roots, at least to some degree.
With the gardening in mind, I’d scavenged some old carpet from the side of the road. This was laid in to protect the weed mat against garden tools, and to provide an additional layer of proofing against roots. (And yes, I’m aware of the debate about whether carpet should be used or not for these purposes; in the end I decided that more was better than less when it came to roots.)
Getting 1.5 tonnes of soil back into the bed was my final workout. Having read that roots breaking down release toxins, I carefully removed the camphor laurel roots when refilling the bed, which slowed the whole process down.
Hopefully that’s all fixed now, and I can get back to growing vegetables!