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Garden Problems - Space Invaders (Root Invasion)

If you are establishing a new garden bed, or are revamping a new bed, it might be time to consider whether you need to do something about space invaders.

What am I on about? 
Well, we have had several customers over the years giving us feedback their gardens aren't thriving (even after purchasing our amazing soil!) and Paul has paid them a visit, only to discover that roots infiltrating the garden bed is the main problem.   (Photo on the right shows roots in a garden bed.  Note:  thick, black strips are retic, small pale bits are straw.  These tree roots are the straight, brown pieces - and there was a lot of them!)

Don't underestimate a tree's ability to sniff out the water and wonderful nutrients you are giving to your vegetable crop. Tree roots are capable of travelling many metres (we've seen them up to 15m away taking up most of the space within a 6 week period). Where space is a premium, of course you may well need to plant much closer than this to a tree (or nearby shrubs, or even a fence - with your neighbour's plants quite close by). Unfortunately plants don’t recognise fences; and if you’re feeding the soil on your side, you can bet your neighbour’s plants on the other side will be chasing those nutrients too!

The best way to solve the problem is to use a raised bed and include some kind of root barrier material.

There are a few options:

  • Geotex is a felt-like grey material especially designed for the purpose. We have found even this often fails if used in a single layer, but if you double up (or even use three layers) it is very effective.   We now have 2m wide Geotex material available (shown here) for sale off the roll.
  • Old carpet or carpet underlay (often given away by carpet shops or found on roadside pickups). Some organic growers have concerns about chemical treatments on carpets; but depending on where you stand on this issue the recycling of a waste product is admirable. The advantage is that carpet will normally allow water to permeate, so you shouldn’t have problems with waterlogging.
  • Newspaper or cardboard. This is easy to get hold of and is cheap, but be aware you need to use a THICK layer, and it is going to break down over a season or two; however you may wish to revamp your beds in this time anyway. Make sure layers overlap really well – as root hairs will work their way between them in time.
  • Plastic sheeting works really well, but be aware you will have drainage problems, as any excess moisture can't drain away. Make sure your bed is deep enough (probably 40cms at least); and it might be a good idea to use approx a 10cm layer of blue metal or stones at the base to help avoid waterlogging the soil. We would also recommend you make small slits in the plastic to help with this. If you put them in the corners of the bed; a little way up the sides, you can easily inspect these from time to time and assess whether any roots have found their way in.  Black plastic will degrade quickly in sunlight (unless it is UV stabilised); and you will have to decide for yourself whether the (possible) leaching from the plastic is an issue for you.  Pond liner material (designed for drinking water) is another option; although more expensive.  If you are going to use plastic sheeting, consider making a 'proper' wicking bed out of it.  See our fact sheet here for more details.
  • Any of these methods will certainly help, but considering how fine and robust tree roots are, always be vigilant. You may need to replace your barrier material from time to time, but you should get quite a few growing seasons out of the bed first.

If you are having problems with an existing garden bed, we suggest you go and investigate your garden. If it is full of fine, fibrous material you may have a problem. If the roots belong to expired crops, this is fine, as the material will break down. But if it is living tissue, you have a space invader sucking your bed dry of all the goodies you are lovingly providing your vegies and herbs. Unfortunately there is little you can do other than dig the bed and line it with one of the methods outlined above. But at least if you are aware of the problem, you can provide additional water & nutrition to your crops while they’re producing and hopefully achieve a harvest.


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