A root barrier will prevent damage to sidewalks, retaining walls, etc. The tree on the left had a root barrier installed in 1983 and shows no damage to sidewalk. Sidewalk on extreme left shows upheaval because no root barrier was installed.

Walking through a forest, park, or even in your yard, the graceful beauty of trees pleases the eye as it provides welcome shade, and makes us all breathe a bit deeper. Adding trees to a landscape increases the visual value of a property, and perhaps the monetary value as well. We?ve even found a way, using containers, to bring large trees indoors, to aesthetically enhance our interiors, such as malls and office buildings.

However, as you?re enjoying the scenery, be careful that you don?t find yourself stumbling over tree roots that have pushed their way to the surface, or worse, roots that have pushed up a portion of the pavement. Tree roots can be one of the strongest forces of nature, and when placed around concrete, asphalt, or along retaining walls or foundations, they can wreak havoc. Annually, they cause billions of dollars in damage to sidewalks, streets, foundations, and retaining walls. In California alone, it?s estimated that it cost $62 million in 1999 just to repair sidewalks damaged by tree roots. When you throw in the cost of pruning those roots or planting new trees, and monies paid in lawsuits for citizens tripping over cracked or buckled concrete, maintaining those lovely trees has made many a city council want to pave over every green space in sight. All of these costs can be dramatically reduced by using root barriers.

Roots deflected from sides of the root barrier now grow down.

Tree roots are very aggressive, growing near the soil?s surface in search of water, nutrients, and oxygen. They can extend underground, spreading outward, two to three times the diameter of the tree canopy. As the tree grows, the roots grow, becoming larger and larger, exerting tremendous pressure on concrete and asphalt. It is these surface roots, buttressing upward, that produce the damage to hardscapes (streets and sidewalks) in cities across America. These same roots can encroach on turf grasses in all landscape environments, including parks, golf courses, schools and green belts, and interfere with mowing equipment, as well as pedestrian traffic. The severe problems of tree root damage, tree loss, and our ability to manage the living root system has led to the invention of the tree root barrier.

Early on, the most common solution to prevent tree root damage was to select specific species of trees that would grow within the constraints of our urban designs, and which have fewer surface roots. For years, city foresters avoided shallow-rooted species like maples, sweetgums, poplars, and American elms. They also stressed good design by not planting trees that grew taller than 30 feet in spaces that had only 3 to 4 feet between pavement and sidewalk, and never planted trees over 50 feet in 5- to 6-foot spaces.

Beyond tree selection, the only other solution was to root prune the tree regularly, and/or replace it, if necessary. Root pruning is costly in man-hours and equipment, and it can seriously damage the tree. Some trees are more sensitive to root pruning than others. Elms, honeylocusts, maples, sycamores, and ginkgos don?t tolerate root pruning well. Older trees don?t like it, though younger ones fare better. There is the danger of disease, especially when roots are not clean-sawed. There is also the risk of pruning too much, and not leaving enough anchor roots to stabilize the tree.

Root Barriers
Twenty-five years ago, an innovation proved that tree roots and hardscapes could exist without too much difficulty. There were many earlier ideas such as concrete, sheets of plastic film, tar paper, bottomless containers and chemicals, but the invention of the 90-degree, raised rib molded to plastic panels finally opened the door to tree root management.

In 1976, Deep Root Corporation introduced the first manufactured tree root barrier. It was a simple idea that actually worked. The root-deflecting ribs proved that tree roots could be guided downward below the barrier edge, into the sub-soil. This was quite an improvement over costly repairs because it allowed the tree roots to grow naturally, but in a specific direction. The product patented a 90-degree root-deflecting rib molded of impervious, smooth-walled plastic. The root barrier set into motion the new technology and science of tree root management.

Ron Hill, currently a specifications representative with O?Connor Sales, was the first representative to introduce the new root barrier technology to Southern California. He saw the value of this new product, and has witnessed the development of a variety of root management products.

It was no easy task trying to convince city architects, planners, street tree project managers and anyone else who would listen, of the value of root barriers. Over the years, Hill has taken numerous arborists, educators and landscape architects to tree sites that have been growing in surround root barriers for over a quarter of a century, and the hardscapes are still intact.

?These root barriers have been able to extend the life of the tree/hardscape by at least ten to fifteen years, saving cities years of potential street, curb and sidewalk repair costs,? explained Hill. ?Root barriers have allowed cities a wider variety of street trees, which can be effectively managed.?

?The challenge is to meet somewhere between ideology and practicability,? says Hill. ?All too often, trees are planted in a restricted urban environment, and root barriers have proven the real champion in those tight situations.? He sums it up in his Golden Rule of Root Control: ?The root barrier planting system must address the immediate and long-term health of the tree, while achieving long-term hardscape integrity, and ultimately provide a safe pedestrian environment around the perimeter of the tree in the decades to come.? For the past twenty-five years, Hill has dedicated himself to spreading the gospel.

The roster of those using root barriers is impressive and growing. Disneyland has had root barriers installed at its theme park since 1986. The US Department of Agriculture building in Washington DC, Harvard University, Apple Computer Research & Design Campus, the St. Louis Zoo, the Atlanta Olympic games, and the New York State Department of Transportation are just a few.

The White House, Santa Barbara Zoo, Disney World, Florida University, the Mirage Hotel, the MGM Grand Hotel and Theme Park, and the Red Lion Inns add to the list.

Tree root barriers are offered in a variety of forms. Some are the pre-formed container style, others are plastic sheets with glued-on ribs. Still, the standard for long term root management is the injection-molded modular panels that lock together to form both linear and surround barriers. There are also root barriers made from non-woven filter fabric.

All root barrier products are designed to function in a surround or linear application. All plastic root barriers have vertical root deflecting ribs to encourage root deflection.

NDS, Lindsay, California, manufactures its product under the Shawtown name. Deep Root Corporation, San Francisco, California, and Century Root Barriers, Anaheim, California, manufacture and market their products under their respective names. Century also makes root barrier rolls that come in 20-foot sections, have a flexible top edge, and will only have one joining when installed. They are made of 50 percent recycled polystyrene with UV inhibitors and is .60-inches thick.

?Always buy a quality product,? says Tom Smith, president of Century Root Barriers. ?There are a lot of look-alikes out there that have joinings that can be pulled apart by hand, or products that have ribs glued on in the field.?
Some city planners are just plain convinced that root barriers don?t work. One city in California recently stopped using root barriers to save money on initial installations, and because they thought the barriers didn?t work. According to Smith, some 14 to 18 months later, the sidewalks had already lifted. The city is now planning on grinding the concrete down.

Any of the barrier panels can be used in either linear or surround installations. Linear applications are usually done between sidewalk and street. The panels are installed against the hardscape, on each side of the area where the tree will be planted. A long series of panels, joined together, will follow the sidewalk or street.

Linear installations allow the tree to use all of the available soil for root development, which will produce a healthier tree. Surround methods are used when you have a smaller space in which to grow a tree. These are often in sidewalk cutouts or along parkways.
Any of these products will work if they are installed properly. The vertical ribs all face the tree, so that the roots can find the 90 degree strips and be directed downward.

Root barrier installed around tree in foreground . . .
root barriers were not used on the trees in the back.
Notice tree roots growing on the surface.

Chemical barriers
Another type of root barrier is the herbicide-embedded fabric called Biobarrier. This non-woven, polypropylene geotextile fabric has plastic nodules of the herbicide trifluralin placed in even rows along the fabric. Trifluralin is released as a vapor 1 to 2-inches around each nodule in time-release form. As the tree roots approach the fabric, root tip cell division is stopped, and the tree?s roots don?t grow in that direction. Since the barrier is a fabric, it can be wrapped around the tree roots, or even pipes near trees, to keep the roots from damaging the pipes. It also allows water and nutrients to pass through it, nourishing the tree.

The herbicide trifluralin, also called Treflan, has been used in agriculture for 35 years. It is a pre-emergence specific herbicide for grass and broadleaf weeds.

Biobarrier is installed completely underground and cannot be seen. It has been used in parks, golf courses, along airport runways, on sidewalks, near building foundations, around pipes, in dams and levees, along bike paths, near tennis courts, swimming pools, septic fields, hotels, irrigation lines, burial vaults, and landfills.

Tex-R Fabric Root Barrier is a non-woven filter fabric with a coating of Spin-Out, which is heat-bonded to the fabric. It is non-toxic and doesn?t leach into the soil. Roots are stopped at the barrier, while the fabric allows water and nutrients to pass through. It is very thin, only .7mm to 1mm thick and is installed 1-inch below the hardscape, and glued to the hard surface by a silicon seal.

You can see the roots growing downward once the root barrier was removed.

Installation of the product usually requires two people. One will hold the fabric in place, while the other backfills the trench. The product must be installed within 12 hours after opening the sealed wrapper. High temperature and sun will reduce the life of the product. However, the cooler the area, the longer that the product will last in the ground.

Root barriers work. The physical barriers are in use across the southern tier of the United States. Some have been introduced along the East Coast, in Massachusetts and New York. It will be a challenge for the industry to work out solutions for colder Northern areas that suffer from freezing and frost heaving, which could move barriers around.

We can enjoy trees and benefit from them in the midst of our busy cities or wherever we play ? on golf courses or amusement parks?and we can still prevent costly damage to our sidewalks or streets.

We are the stewards of our environment, and ultimately bound to our forests and landscapes. As the keepers of trees, we must achieve quality in the administration of our responsibility to them.

June 2001