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Versatility of Geotextiles in the Landscape

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The simplicity of landscape fabric belies its versatility. Like a jack-of-all-trades, this product can be used in many different settings, for many different reasons. Whether it’s for filtration, reinforcement under pavers, weed abatement, or even keeping wildlife at bay, this product can do it all. Better still, it comes in a convenient roll and can be cut to fit.

Landscape fabric is part of a group more formally known as “geotextiles.” You might know it as reinforcement cloth or weed barrier, but chances are, you know it well and you think it’s invaluable.

Used for both landscape and hardscape, landscape fabric is usually made from permeable polypropylene, and can be biodegradable or non-biodegradable, woven or non-woven, in a wide variety of thicknesses. It’s used for separation— between layers of soil—as well as for filtration, reinforcement and drainage.

But it doesn’t stop there. Protection, usually from the weather, is another vital use for these innovative materials. When a frost warning comes, draping geotextile fabric over threatened plant material can help it retain heat. Keeping plants just a few degrees warmer may be all that’s needed to keep them from freezing. Conversely, like people with fair skin, some plants can’t take too much blazing sun, either. Geotextiles can provide a layer of “sunblock” against a scorching hot spell. Fabrics are available that can provide anywhere from 10 to 90 percent protection from Old Mr. Sun’s ultraviolet rays.

Control those weeds

But in the landscape profession, geotextiles’ most common and familiar application is as a barrier material to keep weeds out. Many landscape contractors depend heavily on these fabrics for this purpose.

“We use a ton of geotextiles,” says Todd Christianson, sales president and construction manager at Titan LLC in Anchorage, Alaska. He says that he’s used landscape fabric in his business “since day one.” “We use quite a bit of the commercial weed mat up here, because weeds are a big problem. People don’t seem to realize that we get a lot of sunlight in the summer, so weed growth really creates havoc.”

Weed control fabric is much more sophisticated than the plain black plastic used to make trash bags. “About 20 years ago, they started coming out with geotextiles,” said 39-year green industry veteran Stan Hoglund, owner of Hoglund Landscape, Inc. in Fargo, North Dakota. “Before that, we used black plastic. It kept weeds out, but everything else, too. When they started making landscape fabric, I thought, ‘This is wonderful—it lets air, water and nutrients get to the roots.’”

However, to get the maximum benefit from these products, you need to remember the old axiom: “When all else fails, follow directions.” You must make sure that they’re being installed correctly.

“Weed control fabric is great, but it’s way overused,” said Rolland Kuhr, owner of Naturescape Designs in Jackson, Wyoming. “Over and over, I’ve found it to be improperly installed. I can’t tell you how many times I’ve taken on a new client and found fabric that had been placed tightly around a three-inch-caliper-width tree. Here it is, fifteen to twenty years later, and the tree has grown to an 8-, 10- or 12-inch-caliper width, and the fabric is literally inside the tree, embedded in the trunk, and I can’t get it out.” He suggests placing weed control fabric no closer than four feet from a tree’s trunk.

“We put guidelines out there for installers,” said Matt Kocian, product manager for Typar, a division of Old Hickory, Tennessee-based Fiberweb, Inc. “What we’re dealing with in a case like that is somebody who didn’t read the directions, or didn’t care.” He explains that you’re supposed to cut an ‘X’ in the fabric, then install or plant into the middle of the ‘X.’ Then, as the diameter of the trunk grows, you won’t have ‘girdling,’ which is the term for what Kuhr’s describing. “If you just make a hole, you’re not allowing for that fabric to expand. So if you ‘X’ the spot, as the tree grows, the ‘X’ just folds those tongues back.” It also won’t leave bare surface soil for weeds and in-competition vegetation to move in directly adjacent to the tree.

When using geotextiles, it might be good to keep in mind something Kocian said: “The challenge in landscape is always being able to predict and prepare for changes that will come.”

You can also get landscape fabric that’s impregnated with trifluralin, an herbicide that inhibits the growth of both weeds and roots. Hoglund often uses it for both purposes, having installed it in the landscape at three different hotels on the Las Vegas Strip.

“This product (called Biobarrier) was developed 35 years ago, specifically for stopping roots from naturescape designs/adam J. howard penetrating hazardous waste sites,” said Kocian. “Roots were getting in there, pulling up those toxic materials and putting them back into the ecosystem.”

Hoglund sometimes finds that he needs to protect his retaining walls from roots. “If there’s a tree up against a wall we’re building, or even as far as 20 feet away, we’ll use a barrier so the roots don’t come through. We’ve seen cases where roots will actually blow a wall up.”

But an herbicidal solution isn’t right for everyone. “Chemical herbicides aren’t healthy for soil microorganisms, in my opinion,” says Larry DeWitt, president/CEO of the De- Witt Company in Sikeston, Missouri. “This is not to say that all herbicides are bad. I praise the new organic forms, like the ones made from corn gluten.” DeWitt confesses that he uses them on his own farm, but not in his personal vegetable garden. If you do use them, he recommends a yearly microbial application to give back what herbicides kill, as well as applying microbes to all newly excavated soils.

Wildlife fencing Geotextiles are useful not just for keeping flora—in the form of weeds and roots—at bay, but fauna as well. Polypropylene bird and deer netting is made by the same companies that make weed and root control fabrics. That’s a relief to both Christianson and Kuhr. It seems that moose, prevalent in both Alaska and Wyoming, like to nibble on soft tree and branch bark. To protect their clients’ investments, both of these landscape professionals use poly netting as moose barriers.

“Moose are like dogs in the neighborhood,” says Christianson.

“Everybody up here has two or three they know by name. A moose can snap an $800 tree in half in a second. They can come in and just take out a landscape.”

To keep trees from becoming moose munch, Kuhr wraps the lower branches and trunks of aspens, cottonwoods and willows with geofabric netting from mid-October to early May. “Snow covers up the first couple of feet, so I wrap them within two feet of the ground.” Elk are just as destructive, according to him. “In the fall, elk bulls get into their rutting season. Their hormones go crazy, and they just run right into trees and tear ’em apart.”

Hardscaping and erosion control

Hoglund finds geotextiles invaluable in doing paving and erosion control work. For those applications, he uses a heavy-duty, non-woven polypropylene geotextile that he refers to as “stabilization cloth.”

“We do a lot of hardscaping. We use the stabilization cloth for building roads and rock-faced block retaining wall systems, or under pavers. For roads, we always put it underneath the gravel; then you don’t get any soil integration. It just stays there.”

Josh Kane is president and head designer for Kane Landscapes, Inc. in Sterling, Virginia, and a Landscape Industry Certified Technician.

“We use the non-woven type as drainage filters behind retaining walls, and for soil separation between aggregate stone and natural soil. We also use it around perforated drain pipes, to keep soil out.” He finds that the non-woven type works well for drainage, and the woven type is better under pavers, patios and retaining wall bases. “We use non-woven landscape fabric under our decorative river rock swales to control water running off a driveway into the backyard.”

Hoglund used geotextile fabric heavily with the earlier rock-faced block retaining wall systems, underneath the compacted material at the base as well as behind the wall, to keep dirt and water from washing through the seams. He finds that it’s not needed as much with the better-made newer systems. For those walls, he tends to place drainage tiles covered with geofabric behind them.

For installing pavers, Hoglund has developed a “geotextile sandwich” technique that works well for him. “We get freeze/thaw up here, and what happens is that the ground actually mixes together.” To solve that problem, after excavation and compaction, he lays in the fabric, then another six inches of compacted material. Over that goes yet another layer of fabric. Only then do the pavers and the sand go in.

“If you don’t do that, the sand and the compacted material integrate into the subsoils. But if you sandwich it, you don’t get any of that, because you’ve got the reinforcement cloth there to stop it.” He adds that a lot of contractors will get settling and unevenness in their paver jobs, “but we don’t. We’ve had great success and never get any callbacks.”

Hoglund has had some nervous customers call during the first freeze following installation. “I tell them not to worry, that after the thaw the pavers will go right back into place. I never hear from them again.” He attributes this to the stability of his sandwich technique, and the geotextiles’ porosity. “You want moisture to get through. I’ve seen people putting [ordinary nonporous] plastic underneath their pavers.

Then the water doesn’t have anywhere to go.” That doesn’t work well in the harsh North Dakota winters.

They keep getting better

Landscape fabric is a great tool, but it isn’t foolproof. Another criticism is that sometimes weeds grow right through it. Christianson admits that, “We have to use a pretty strong matting to keep the weeds from growing through the sides between the edging and the mat, or just directly through the textile fabric itself.” Roots can also grow under and over barriers. You need to make sure the fabric is installed deeply enough.

“I only use landscape fabric when I have to,” said Lisa LaPaso, owner of Lisa’s Landscape and Design in Austin, Texas. “I prefer to use four-millimeter painter’s plastic and landscape pins than landscape fabric. Fabric tears easily, especially in the heat we have here in Texas, and then the weeds and roots get through the fabric and make it impossible to get them out.” But she concedes that fabric is good for use on slopes where other types of plastic would not serve the purpose.

Christianson says he’s seen significant improvement in geotextile technology in the 31 years he’s been in the green industry. “It used to be more of a felt-type material, which they still make in homeownergrade. What we use now is much stronger and denser.” However, he thinks there’s still room for improvement. “I still don’t think weed control fabric lets enough water and nutrients get through to the plants.”

Of course, manufacturers of landscape fabric are anxious to allay fears like this and promote their benefits. “Test after test has proven that breathable fabric boosts soils’ cation exchange capacity (soil metabolism) by as much as double,” said DeWitt.

“After 40 years in the weed barrier business, I can assure you with confidence that a layer of polypropylene fabric, which is hydrophobic, placed on top of the soil will reduce plants’ water consumption needs by more than 60 to 70 percent,” said DeWitt. And, according to him, it does this without any side effects to the soils’ vital microbe and earthworm decomposition process.

Continued innovation

Geotextile development isn’t standing still, not with all the manufacturers out there competing for your business. Competition and demand means that landscape professionals can look forward to new products hitting the market regularly.

You may have been in the landscape business longer than geotextiles have. It’s a safe bet, however, that they’re no flash in the pan. Give them a try, and see if there aren’t a few dozen things they could do for you.

 
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