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Question DetailsAsked on 3/28/2014

What is recommended best product for capping tree root that's 15 yrs old (or root barrier) and is there basic rules

What type of plastic root barrier and the dimensions is best to use.

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1 Answer


Here is a short article on that specific question -

You can find lots more info using this google search phrase - preventing root growth into foundation

Individually capping cut off roots wth pipe sleeves has been tried but does not work - just slows it up a year or so, then new root tendrils come out up-stem from the pipe sleeve and work that way again.

There are two basic ways that work -

1) poisoning the root or the soil it is growing into, commonly with copper sulfate powder, though that can damage very young or ornamental trees. The plant does not take up much of the copper so established trees and shrubs are no hurt by it - it just prevents growth into the treated area. Commonly used to keep roots out of sewer pipes. Sometimes used along foundations where the original soil is laced with tree roots from trees that were cut down for construction in wooded areas - should NOT be used in direct contact with concrete foundation - used outside a bitumastic or asphaltic foundation coating.

2) putting in an impenetrable barrier as described in the article. You need a barrier material that the plant cannot grow through and is not biodegradable in the short term (all barriers are eventually biodegradable when thinking in terms of scores of years). Concrete has been used but roots will get through cracks. Bentonite blankets have been tried and will stop some roots, but not others, and material costs almost as much as plastic. Steel will work but very pricey to go 18-60" deep. I know article says 18" but while that is true for most nutrient-poor soils, in areas with perched or high water tables within about 10' of the surface lateral roots will work deeper to be in the permanent capillary damp zone a few feet above the water table, and in disturbed soils around construction sites they will also go 3 or more feet deep. You should dig down a couple of places, or use a posthole digger, and find out how deep the root tendrils go in your area of concern - in some areas with water at reasonable depth large trees put lateral roots down to 10 feet or more, and in others with caliche or very low nutrient soil below the topsoil root depth may be limited to a foot or two. Bear in mind when it reaches a barrier tree roots will try to find a way around, so for instance if your general root depth is 2 feet or less, I would use a 3 foot barrier to have a hope of stopping them.

3) Some people also do something that is off-label for the product so technically illegal, and spread or heavily spray a general herbicide like 2,4-D on the trench wall behind the barrier, so roots coming around the barrier hit that and are killed, though that also can act as a systemic poison to the entire plant. Mixing copper sulfate into the backfill in the trench on the side away from the tree can also act as a deterent.

4) Your best bet is a heavy (20 mil or thicker and preferably 30-40 mil fur durability) plastic sheet rated for direct earth burial. Flexible pond and landfill liner like PVC (Hypalon and other brand names) is easier to put in because it is flexible, but also has shorter life in the ground and very short life in the above-ground portion where exposed to ultraviolet light. Heavier, less flexible plastics like HDPE will last longer, but due to stiffness are a bit harder to work with, though not unduly.

5) I would recommend a heavy duty top barrier alongside the top - have the cutoff extend 4-6 inches above ground, but back it up with a concrete curb, 12" plastic or steel edger strip to keep it from bending over or getting torn up by mower, etc. Avoid steel edger in areas where kids play unless you grind the end corners round and caulk a protective slip-on plastic bulb strip on top. Also keep backk from areas where it could get driven on or hit by snowplow or snowblower.

Answered 6 years ago by LCD

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