Fabric in the Landscape
|By ELIZABETH LEXAU|
WHAT STABILIZES SOIL, RETAINS moisture, saves on mulch, aids in filtration, reinforces and protects, and oh, yes . . . minimizes weeding? The answer is landscape fabric. Commonly known as a weed-barrier, landscape fabric isn’t just for weed control. It’s a multi-tool rolled up in a convenient, easy-to-use package.
Landscape fabrics come in many flavors. They can be woven or spun bond and vary greatly in their weight, strength, permeability, life expectancy and other factors. These fabrics have come a long way since their early days. Stronger, longer lasting materials, greater UV-resistance, better weed suppression, and a wider array of products are making it easier for contractors to choose fabrics for diverse needs.
Because they vary greatly, there isn’t a one-size-fits-all fabric for every application. It’s important to choose one that’s recommended by the manufacturer for a specific purpose. Whether it’s going to be used as a weed barrier, a separation layer, a protective buffer under a water feature, or as a reinforcing layer under a driveway or patio, you’ll want to choose one that has the specs to suit the job.
Keeping weeds at bay
One of the major uses of landscape fabric is to help control weeds in planting beds, under decks and beneath patios and paths. Fabrics work to block weed growth by shutting out light while allowing air and moisture in.
For many years, plastic sheeting was used for the job of weed control. While plastic is very effective at suppressing weeds, it also has a serious side effect that makes it a poor choice in planting beds. “If you use plastic, you suffocate the soil,” says Larry DeWitt, president of the DeWitt Company, Sikeston, Missouri. “You suffocate the living organisms, and the soil dies.”
Plastic prevents the air and moisture exchange necessary to maintain healthy soil ecology. Even when holes are cut into plastic to allow for plantings, the moisture and nutrient-starved soil underneath most of the bed prevents plants from thriving as they grow and their roots extend. Like plastic, fabrics block the weeds, but they do it while allowing soil to breathe.
When used in planting beds, fabrics don’t just let moisture in, they also help keep it in. “Landscape fabrics limit evaporation, so they are very important for water conservation,” says Steve Gambla, president of Ground Cover Industries, Arlington, Texas.
Using landscape fabric adds value to an installation without a lot of extra expense. “Fabric is such a minute expense in a landscape job,” says Gambla. “You may spend $100 in fabric on a $3,000 project. It’s a no-brainer. This will add quality to a project with very little extra cost.”
“We primarily use it in flower beds and underneath trees,” says Chad Snyder, owner of Snyder Landscaping and Lawn Care in Mitchellville, Iowa. “There’s definitely a big difference when you use it. You can’t see it, but if it’s not there, you know it. You’re going to see weeds and grasses. If you have it, you’re going to notice a clean flower bed.”
Some contractors use fabric under planting beds whether they use rock or organic mulches. Others use it only under rock mulch because they prefer to allow their organic mulches to decompose freely into the soil. For those who prefer to use old mulch to build new soil, a shorter-term fabric is an option. In this case, the fabric is removed and replaced every few years to allow decomposed mulch to combine with soil.
No matter what kind of mulch is used, installing landscape fabric underneath can significantly reduce the amount of mulching material needed. “Wood mulch will last longer and stone mulch will stay cleaner and last even longer,” says DeWitt.
Fabric keeps mulch from compacting into the soil and also makes it easier to move the material later—for example, if new plantings are added down the road. Organic mulches won’t break down as quickly because they don’t have direct contact with the soil.
Generally, the heavier the fabric, the better it is at weed suppression. However, it’s important to pay attention to other factors, especially permeability, when choosing landscape fabric for planting beds. The mesh needs to be fine enough to block weed and grass growth but large enough to allow water and air to pass. If fabric isn’t sufficiently permeable, it will block moisture and nutrients, too. It can also create a runoff problem in the bed that may erode soil or wash away mulch.
Manufacturers list permeability information in product specifications. But DeWitt says a simple home test can also give you the answers you need. “Just cut a 1' x1' piece of fabric and run it under the kitchen sink,” he says. “The water should run freely through it. You should also be able to breathe through it like you would through a dust mask. If you can breathe through it, so can the soil.”
It’s important to remember that while landscape fabrics go a long way toward controlling weeds, there is no such thing as a maintenance-free planting bed. Many of today’s strong, heavy-duty breathable fabrics are very effective at preventing weeds from growing through the barrier and keeping roots from growing down through it. Some even guarantee 100% weed control. But nothing can prevent weed seeds from blowing in from outside of a bed and settling into mulch. And weeds are amazingly good at sprouting in any medium. That’s why we call them weeds.
“Weed barrier is not a guarantee, no matter what kind of mulch you use,” says Steve Berg, senior landscape architect with David J. Frank Landscape Contracting, Germantown, Wisconsin. “Wood mulch breaks down and becomes a soil mass of its own. In stone, there’s still dust that will fall into cavities of rock and create a small area that plants can survive in. But with a good weed barrier, the roots stay on top of the barrier and the task of removing that weed is much easier.”
Of course, weed control isn’t just for planting beds. It’s also needed under decks, patios, and other hardscapes. “Landscape fabric has been an especially helpful alternative for us under decks,” says Berg. “We used to put stone down to keep weeds from growing. Now we just put down the weed barrier, add a little weight on it, and staple it down. It’s saved us quite a bit on material for that application.”
Installing weed barrier
To get the most weed protection from any landscape fabric, it’s important to prepare the site and remove as many existing weeds as possible. “We always recommend that you start with a pre-emergent herbicide to make sure you kill any vegetation before you install,” says Gambla.
Ground should be smooth and free of debris to ensure good contact. Weed barrier can be installed either before or after planting, depending on the size of the bed, the spacing of the plants and the preference of the installer.
If plants are installed after the fabric has been put down, the fabric is sliced with “X’s” where plants will be inserted. Then the flaps are folded away to make a hole. After plants are inserted, the fabric is folded back close to the plant base. If fabric is to be placed after planting, X’s are measured, marked, and cut into the fabric before it is laid down. Then the fabric is placed over the bed and the plants are pulled through X’s.
When laying fabric, it’s important to overlap pieces to make sure there are no gaps that would allow light in. It’s also important to fasten the fabric securely with pins around the edges and at the overlaps to keep it from shifting and to keep determined weeds from pushing their way up far enough to catch some rays.
“Make sure you overlap sufficiently,” says Snyder. “If you don’t you’re going to have weeds that will squeeze through. When laying it out, make sure you extend it well over the edging. It’s always easier to overlap the edging and trim it off later than to come up an inch or two short.”
Weed control is just one way today’s high-tech fabrics are used in the landscape. They’ve become a multipurpose tool for many jobs that require filtration, separation, stabilization, or an additional protective, permeable barrier.
Used as a stabilizing layer and for separation under pavers or crushed rock paths, they minimize the effects of frost heave, and prevent pavers and aggregates from sinking into the subsoil.
“It works very well for any job where you need a water-permeable membrane,” says Glenn Richardson, landscape designer with Cedar Run Landscaping, Aldie, Virginia. “We use it frequently underneath concrete pavers. Despite all of the ground preparation we do, there might be a chance for settling. The landscape fabric will help even out the stresses. This is especially important in any kind of driveway situation.”
Fabric also has many uses when it comes to filtration. It’s used around perforated pipe, in trench drains, and behind retaining walls. “One of my favorite uses is in dry stream beds used for surface drainage,” says Richardson. “We line the bottom of a ditch with gravel and perforated pipe to redirect runoff. We put the fabric between the gravel and the soil to keep soil from infiltrating the gravel and the pipe.”
Landscape fabric is also frequently used as an economical protective layer under ponds and other water features. “This is a good way to help ensure that we don’t have punctures from roots into the liner membrane,” says Richardson. “It will also help control movement of soil under a new pond.”
Berg uses it in pond applications as well. “It serves as a conduit under the rubber liner to allow for gasses to dissipate. It also protects the rubber liner from sharp edges.”
Berg says fabric has enabled him to create cleaner, higher-quality ponds with less material costs. “We used to put down three to five inches of fine sand, then the pond liner, then a sand soil mix on top of the liner. There was the expense of purchasing the sand and the expense of hauling it. The water would be cloudy until the sand soil mix settled.”
“Now, I can run a fabric down there as a buffer and put rock right over the liner. The fabric protects the liner and we’ve also minimized the cloudiness of the water. It saves material and a lot of effort and also provides a cleaner more established product,” Berg continued.
Not all fabrics are suited to all purposes. To avoid project failure, only use fabrics that are specifically recommended for a particular application. In general, woven fabrics have lower permeability but higher strength. This makes them suitable for landscape applications in addition to stabilization applications. Spun bond fabrics are generally more permeable and are suitable for landscape as well as drainage, filtration and soil separation needs.
You don’t see them. They’re hidden away under mulch, beneath patios, and behind walls. But today’s high tech fabrics are working hard to keep landscapes looking good.