Root Barriers for Trees

Root barriers of several basic designs can prevent damage by spreading roots.


Root barriers for trees are designed to prevent roots from growing into drainage pipes or under sidewalks, driveways, patios or building foundations. Deflector, trap or chemical inhibitor barriers will all work in some circumstances. Their advantages and disadvantages depend on your soil, climate and the kind of roots you are trying to block.

Deflector Barriers

Deflector barriers made of wood, metal or solid plastic redirect or block roots to prevent them from growing into an area. They're most useful for blocking shallow roots or small roots and pushing them to greater depths. Although barriers as thin as 2/3 inch are effective, thicker barriers are easier to install and can block more aggressive roots. Solid deflectors may block the drainage of water from the soil around a tree, subjecting the roots to fungal diseases. In order to promote drainage, there should least 8 inches between the bottom of the barrier and the top of the layer of ground water. If deflector barriers are installed in climates that alternately freeze and thaw, they can cause the soil to heave.

Trap Barriers

Holes in trap barriers accept roots, then strangle or constrict them, preventing them from growing longer and larger. Trap barrier materials include permeable woven and non-woven fabrics, welded fiber sheets and screens. Barriers with small holes work better than ones with larger holes. Effective materials include copper screen with 1/16-inch openings and nylon fabrics with 1/26-inch openings. Traps with even smaller openings include non-elastic, synthetic and weld-woven fabrics. Trap barriers have the advantage of allowing water to pass through their holes, a necessity in rainy areas.

Chemical Inhibitor Barriers

Barriers saturated with toxins or chemical growth agents restrict the growth of roots by inhibiting the growth of cells at their tips. A mixture of 3 1/2 ounces of cupric carbonate and 1 quart of white acrylic paint applied to a solid sheet or wall is effective in controlling roots. Alternatively, a geotextile fabric containing trifluralin inhibits root growth. The roots do not transport trifluralin into the tree, and it is not detectable beyond 4 inches from the barrier. A trifluralin barrier should be applied at least 60 inches deep or roots will grow under it and up the other side.

Installation Basics

If you place a barrier too close to a tree's crown, the roots will encircle the tree, inhibiting its growth. In what is called the "flower pot" effect, circling roots can cause the tree to become unstable. The optimal distance for a root barrier is at least 6 feet from the base of the tree, depending on the diameter of the tree. At a minimum, a root barrier should be placed at a distance of three times the diameter of the base of a mature tree. If your barrier is too shallow, roots will grow under it, and if the top of the barrier does not rise above mulches or soil, roots will grow over them.

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