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.


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!

8 thoughts on “Rebuilding our raised garden beds (the fight against roots continues)

    Carolyn said:
    March 17, 2013 at 11:40 am

    Hi James, yes indeed…. it is a painful process…. to discover that all that hard work and absolutely beautiful soil you created has been taken over, insidiously but surely, by tree roots, but take over they do!!! 😦 I admire your ingenuity….. if I might offer a very small, extra little piece of advice (!), just be sure that the level of your drainage holes is above the ground where you can see them. Tree roots still love to grow into holes if they are below ground level, or where you can’t see them, and especially if it’s dark and damp. I’ve discovered this also!! They will want to go back to where they previously were, to find all those lovely nutrients they enjoyed for such a long time! They’ve got a mind of their own…. you’re dealing with super intelligence here!!

    Trust me, I’ve learned the hard and painful way…. and it’s cost me a fortune in the process, but now I grow in giant pots, and it works a treat. The worms love it too, that lovely little place, all rich and nutrient-loaded, and safe from the world. I started using terracotta pots, but discovered I was losing moisture in massive amounts during the heat due to evaporation through the pottery. So now I use giant plastic pots, which I didn’t want to at first, but they work beautifully….. So now, the plants are happy, the worms are happy, the soil is divinely happy, the tree roots have gone elsewhere in search of food, and I’m happy! 🙂

    Summer crop of pickles and chutneys | Lewisham House said:
    March 28, 2013 at 12:09 pm

    […] already given away or used. That’s not bad considering that half of our main raised beds were attacked by roots, and therefore struggling to produce […]

    […] of the green roof. On top of that I installed a layer of 20mm Atlantis flo-cell (left over from the reworked raised garden beds). A layer of geotextile then keeps the soil out of the drainage […]

    Keren Lavelle (@sleepingdingo) said:
    September 21, 2013 at 5:48 pm

    I’m intrigued and a little daunted by this information, James. My Marrickville garden is also being invaded by roots and suckers from a giant deciduous tree next door which also now shades my garden significantly in summer. I was thinking that I could grow veggies in corrugated iron tubs/garden beds but I realise I’m going to run into the same problem as you have. I’m not so handy as you and I don’t have a hole saw… it’s a pity that somebody doesn’t manufacture garden beds designed for this problem. But thanks very much for the information!

    Lucy said:
    March 1, 2014 at 10:42 am

    Thank you very much for the info. I’m going to refurb my beds just as you explained. Do you have any further tips now you are one year on?

    Charlie Thomas said:
    May 9, 2014 at 11:43 pm

    Wow. A very thoughtful solution. I’d duplicate it, but I’m wondering if you can provide some feedback on the results a year later?

    Stephen said:
    May 28, 2016 at 7:15 pm

    I hate to say it, but I can’t see this stopping the roots. I suspect they will hunt down the moisture provided and will be back in your bed. For my beds the only solution was a solid barrier, even then they try get around the barrier hunting down any hint of moisture. Maybe I have more trouble being low rainfall area…

    Converting to a wicking bed « Lewisham House said:
    January 22, 2017 at 10:00 am

    […] 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, […]

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