The tree you plant this fall is about as thick as a broom handle. In fifteen or twenty years its roots will be under the sidewalk, the driveway, and maybe the sewer line. In most of California, that sidewalk is your problem.
Fall is planting season here, and a lot of trees are going in. San Francisco Public Works is partway through its 3,500 Trees Project, with planting running through 2029. Planting day is also the easiest chance you'll ever get to deal with roots, because the hole is already open.
We sell copper root barrier, a woven copper mesh you trench in between a tree and whatever you don't want it lifting. Here's who pays when roots win, how a root barrier works, what copper does to roots, and how to put one in.
Who Pays When Roots Lift the Sidewalk
California's Streets and Highways Code puts the sidewalk on the owner of the lot next to it. Section 5610 says owners shall maintain it so it "will not endanger persons or property." Each city decides how it applies that when a street tree did the damage, and the three biggest Bay Area cities do it three different ways.
- San Francisco. Since July 1, 2017, StreetTreeSF has Public Works caring for the city's street trees and repairing sidewalks they damage. Owners can opt out and keep caring for their own tree.
- Oakland. Owners repair the sidewalk next to their property, including damage from street tree roots. The city used to take responsibility when the tree was an "official" tree. It no longer does, after the Urban Forest Plan it adopted in fall 2024 flagged problems with that practice. A typical sidewalk permit alone is $1,060.35 on the 2026-27 fee schedule.
- San José. Owners are responsible for the sidewalk, park strip, and curb next to their property, and for the street tree itself. The city offers financial help for required work at owner-occupied single-family homes.
It adds up. A survey of 18 California cities, published in 2000, estimated that about $70.7 million a year was spent statewide on conflicts between street tree roots and sidewalks, curbs, and pavement. The cities said the two biggest factors were cramped planting space and the choice of species. In other words, a big tree in a narrow strip.
How a Root Barrier Works
A root barrier doesn't stop a tree from growing roots. It controls where they go. A barrier along the edge of the concrete sends roots deeper, so they run well below the slab instead of right up against the underside of it, where they do the lifting. In a Bartlett Tree Research Laboratories trial, vertical root barriers resulted in fewer and deeper roots under the pavement.
Three things make the difference.
- Go deep enough. A root that reaches the bottom edge can grow under it and turn back up on the other side, which researchers have documented. A review of about 40 years of root barrier research found most experiments used barriers around a foot deep, and that's often not enough. Our rolls run 18 to 48 inches, and for a tree we'd start at 24.
- Run it in a straight line along the concrete. Not in a ring around the tree. A straight run works next to a new tree or an existing one, and San José's street tree rules say barriers may only go parallel to the curb or sidewalk.
- Leave the top edge above grade. An inch or two above the soil keeps surface roots from growing over the top.
How Copper Works on Roots
Copper's reputation with roots comes from nurseries. Some growers paint the inside of pots with a copper compound, and when a root tip touches the treated wall, it gets a mild dose of copper and stops. Researchers call it "chemical root pruning", and in some species the root branches more.
In the ground, copper mesh works on roots in its own way, and there's a field study on almost exactly what we sell. In 1993, researchers buried 16 mesh copper screen next to cottonwood and birch trees and dug the roots up three growing seasons later.
- Roots that reached the mesh got choked down. Fine root tips grew into the openings, and as they thickened, the wire squeezed them to the size of the hole.
- Growth past the screen was greatly stunted. Root growth beyond the copper was far lower than with no barrier at all.
Researchers call this a trap barrier. A plastic sheet deflects roots. Copper mesh catches them and keeps them from growing thick on the far side.
Why copper. It's metal with about 68% open area, so water and air pass straight through and the soil on both sides drains normally. That makes it a good fit for planting beds, home landscapes, and runs along driveways, patios, and foundations.
Planting a city street tree? Check the city's spec first. Some cities, Oakland included, call out a specific barrier type for the planting strip.
Where It Goes and What Width to Use
The roll width is the barrier depth, less the inch or two you leave above grade. Within reason, deeper is better. A root has to get to the bottom edge to grow under it, and the deeper that edge sits, the fewer roots make it.
| Protecting | Width we'd start with | Where the barrier goes |
|---|---|---|
| Planting beds, hedges, shrubs | 18" | Along the bed edge, between the plants and the path or lawn. |
| Sidewalk or driveway, small tree | 24" | A straight run along the edge of the concrete. |
| Sidewalk or driveway, most yard trees | 36" | Same, and run it well past the tree in both directions. |
| Foundations, large trees | 48" | Between the tree and the wall, as far from the tree as the yard allows. |
| Irrigation and pipe runs | 24" to 36" | Between the tree and the line, and deeper than the pipe. |
About sewer lines. Roots usually don't break into a sound pipe. San Mateo County's sewer guide says they're attracted by water vapor escaping from small cracks and loose joints, get in there, and can eventually break the pipe. A barrier between the tree and the line helps keep roots away from it, and if the lateral is already cracked, get that repaired too. The lateral is yours. In the East Bay, owners are responsible for the whole private sewer lateral from the house to the main, with exceptions in Alameda, Albany, and Berkeley. In San Francisco, the SFPUC says the entire lateral belongs to the owner.
Before You Dig
- Call 811 first. In California, calling 811 before you dig is a legal requirement, and it covers homeowners, not just contractors. USA North 811 asks for at least two working days' notice, and it's free. A trench along a driveway is exactly where gas, water, and electric lines tend to run.
- Street trees need a permit. San Francisco requires a free permit to plant one. San José requires a free permit to plant, prune, or remove one. Oakland requires a planting permit. Ask what the city wants for root barriers while you're at it.
- Be careful around an established tree. A trench next to a mature tree cuts every root that crosses it. Cutting large roots can hurt a tree or make it less stable, so for anything big, have an ISA Certified Arborist decide where the line goes.
How to Install It
- Dig a narrow trench along the line you want to protect, as deep as the roll is wide.
- Stand the mesh upright in the trench, with the top edge 1 to 2 inches above grade, so surface roots can't grow over it.
- Where two lengths meet, overlap the ends so there's no gap for a root to find.
- Backfill in layers, tamping and watering as you go.
Wear gloves. Cut edges of copper screen are sharp.
Frequently Asked Questions
How does copper mesh work on roots?
Fine root tips grow into the openings. As they thicken, the copper wire squeezes them down to the size of the hole, and growth past the barrier is greatly stunted. In a three-year field study of 16 mesh copper screen, root growth beyond the barrier was far lower than with no barrier at all.
Will a copper root barrier kill my tree?
No. It works on the roots that reach the mesh, not on the whole tree. In a study of copper-treated nursery pots, none of the trees showed copper damage in their leaves. As with any barrier, keep it along the concrete rather than wrapped around the trunk, and have an arborist look at large trees.
How deep should a root barrier be?
Deeper than most people think. A foot is often too shallow. We'd use 24 inches for a small tree, 36 for most yard trees, and 48 next to a foundation or for a big tree with an aggressive root system.
Is this the same as a copper sulfate root killer?
No. Those are chemicals you flush down a sewer line. The label on at least one of them says it's not for sale or use for sewer root control in nine Bay Area counties, Alameda and San Francisco included. Root barrier is solid mesh that goes in a trench.
What about gophers?
Root barrier is made for roots. For gophers, use gopher baskets or heavier galvanized wire, and our guide to keeping gophers out of your garden covers it. If you're planting a tree this fall, the basket and the root barrier go in on the same day.
Why is the mesh turning brown or green?
That's copper doing what copper does. It darkens as it weathers, the same way a copper roof or gutter does. It doesn't mean the mesh is failing.
We stock copper root barrier in 18, 24, 36, and 48 inch widths, in 100 foot rolls, and the same cloth comes as 16 mesh copper woven wire in wider widths, cut to size. Tell us what you're protecting and how long the run is, and we'll quote it. If you want to see it first, we'll mail you a free sample. Family-owned since 1938, when we started on Howard Street in San Francisco. Now we're in Hayward, and a real person answers the phone at (510) 887-8787.
This article is general information about wire mesh, not arborist, engineering, or legal advice. How roots respond to a barrier varies by species, soil, and site. For a large or established tree, or work near a foundation, talk to an ISA Certified Arborist. For street trees and sidewalks, your city has the final word.