Weedcloth Revealed

Headshot of Nan StermanA few years ago, we shot an episode of A Growing Passion about creating waterwise gardens ( opens in a new windowwww.agrowingpassion.com/episode- 405-lawn-gone-waterwise-gardens).

Among the gardens we showcased was a beautiful Los Angeles garden designed by a good friend. For the shoot, he and I wandered through the garden talking about the sloping lawn it replaced. As we walked, I noticed the mulch sliding off the surface, revealing black fabric weedcloth beneath. “Why weedcloth?” I asked him. “I didn’t want to use it,” he said. “It was a requirement.” The lawn replacement was done under a Los Angeles water-agency rebate and one of the requirements was weedcloth.

I was stunned. All the work and effort that went into this beautiful new garden could be wasted by that one misguided requirement.

“Weed cloth,” “weed barrier,” and “landscape fabric” all describe fabric-like materials sold by the roll. The fabric is laid out over bare soil with the promise of a permanent solution to weed problems. Drip irrigation goes beneath the fabric, which is then pinned down with metal staples. To plant, you cut slits in the weedcloth, dig a hole, and plant the plant. Finally, you cover the weedcloth with mulch.

Sadly, weedcloth is not a long-term solution and in fact, is detrimental to the soil, the plants, and the success of your garden.

True, intact weedcloth can suppress annual weeds from developing short-term, but does not stop Bermuda grass or other creeping weeds. They grow out from the edges, emerge from seams, and pop up through holes that develop in the fabric as it ages and breaks down. Annual weeds sprout through those holes, too.

Weedcloth does not stop weed seeds from blowing into the garden, being dropped by birds, or falling off your shoes or your dog’s coat. Those weeds sprout in the mulch that covers weed cloth.

Irrigation under weed cloth is impossible to monitor. If something breaks or starts to leak, you may not notice for a long time, if ever.

Weedcloth is supposed to be water permeable; which may be the case in regions with torrential downpours, but here, water barely penetrates. Soil beneath weedcloth, then, dries out and hardens. Beneficial organisms that keep plants healthy cannot survive under those conditions. And, since this happens out of sight, most people do not notice the transformation to concrete-hard surface until they remove the weedcloth.

Since weedcloth is a physical barrier, it keeps mulch from doing its most important jobs. As mulch breaks down, it incorporates into the soil. That organic matter supports important microorganisms and beneficial insects that help keep plant roots healthy. Mulch also helps heavy soils drain and helps fast draining soils hold water. But when weed cloth is between mulch and soil, none of this happens. Instead, the mulch dries out to dust, and like in the garden I visited, slips off the weed cloth or blows away. It is unsightly and a huge missed opportunity.

Eventually, garden owners wonder why their plants are growing poorly. When they pull back the mulch, they may even find plant roots growing on top of the landscape fabric, rather than in the soil.

After a year or so, weedcloth breaks down. Shredded black strips emerge from under the mulch, making a big, ugly mess. At that point, it has to be removed and has become a big, costly, labor-intensive project.

Forget weedcloth. Instead, opt for a 3 or 4-inch-thick layer of organic mulch applied directly onto the surface of the soil. “Organic” mulch, by the way, is mulch made from leaves, clippings, tree branches, etc.

Mulch delivers on the promise of smothering weed seeds. Weeds that sprout from seeds that blow or drop into mulch are easy to pull out, thanks to the loose, chunky nature of organic mulch. Reapply mulch once a year or so.

If your garden is entirely succulents, use inorganic mulch – rocks, decomposed granite, gravel, etc. – also in a 3-inch-thick layer applied directly onto soil, without weedcloth.

There is one situation where weedcloth performs a valuable service. When you build a dry streambed that will always be dry (rather than a bioswale), weedcloth under the smallest gravel helps keep the gravel from sinking into the soil and disappearing.

Beyond that, don’t fall for the false promise of weedcloth. Your garden will thank you.

Garden expert, designer, and author Nan Sterman specializes in low water, sustainable, and edible landscapes. Nan hosts A Growing Passion, a show about all the ways that San Diego and California grow. A Growing Passion airs on KPBS television Thursdays at 8:30 p.m. Episodes are also posted online at opens in a new windowagrowingpassion.com. Nan is also author of California Gardener’s Guide vII, Waterwise Plants for the Southwest and the upcoming Hot Colors, Dry Garden. More information is at opens in a new windowplantsoup.com.