geotextile

Rebuilding our raised garden beds (the fight against roots continues)

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Everything looks fine on the surface, but underneath, tree roots have taken over it all
Everything looks fine on the surface, but underneath, tree roots have taken over it all

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 first step is to dig out the existing garden beds.
The first step is to dig out the existing garden beds.

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.

That would be the problem then!
That would be the problem then!

I then cut two holes in the side of the tank with a hole saw, for drainage.

Lewisham_20130309_6191

These holes were designed to accept a 25mm threaded tank outlet, as follows:

The threaded tank outlet in place, trimmed a little to fit.
The threaded tank outlet in place, trimmed a little to fit.

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 of Flo-Cell, laid across the bottom of the garden bed
Two layers of Flo-Cell, laid across the bottom of the garden bed.

Two layers were sufficient to get above the tank outlets, and to ensure good drainage.

Closeup of the Flo-Cells -- they're a nice technology.
Closeup of the Flo-Cells — they’re a nice technology.

A small amount of gravel was used to plug the gaps, and a layer of geotextile was then laid across it all.

Geotextile fabric in place -- now to fill the bed back up!
Geotextile fabric in place — now to fill the bed back up!

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!

Yes, it's a garden bed. No sign of all the hard work involved!
Yes, it’s a garden bed. No sign of all the hard work involved!
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