[SidReal]

Hello, I'd like to surround areas of my allotment with a kind of root barrier, wood slabs placed into the ground to prevent weed roots such as cooch grass, bindweed, thistles, nettles etc from tunnelling underground into cleared areas - I wonder, how deep this barrier underground would need to be? I'm sure different for each species of plant - which of these send their roots the deepest, and what depth would this be? I think cooch grass is the main concern for me...

~thanks, ~sid

[aelf]

I would say at least a couple of feet deep. Main problems are:

The wood will rot (even treated wood) after about 5 years as it will be wet all the time.

The roots will force their way between the planks or through knot holes or any (even tiny) gaps.

It will hold back the main force of roots in the short-term tho 

[mobilekat]

I agree with Aelf, especially since the chemicals used to treat wood have changed you will be lucky to get 5 years out of your barrier.

If it was your garden and you were looking for a long term solution I would suggest a wall with deep foundations- I know of people who have literally dug 3 foot down and put concrete and then concrete blocks in to prevent incoming weeds!

You may find one of the plastic options is more cost effective in the long term

Good luck!

[JayG]

I would suggest corrugated plastic sheeting (about £3.47 per metre, 660mm wide from W*ckes, although that's the only place I've priced it.)

Buried vertically in the soil that would give you a long lasting and inpenetrable barried about 2' deep which some roots might still get underneath but you probably couldn't easily dig much deeper than that anyway (or just wouldn't want to!)

A double thickness of pond liner used the same way would possibly be a bit cheaper but despite its puncture resistance I think some weeds could probably still get through it.

[Kleftiwallah]

Get down to your local business site/park and track down the fabricators,  grab all their offcuts of galvanised tin.    Cheers,   Tony.