I’ve seen it again and again. Helping a friend renovate their garden, I dig down a few inches and my shovel becomes entangled in a sheet of black plastic or some other material, collectively known as landscape fabric. Oh boy. Another case of pie-in-the-sky magic weed barrier.
“What’s this?”, I ask.
“Really? Then why are there foot-tall weeds in your garden?”
One of the great gardening myths is that landscape fabric will suppress the weeds in your garden for years. Sold under many trade names and made from an assortment of materials varying from plastic films to renewable sources, weed barriers are also sometimes impregnated with herbicides and fertilizers.
An experienced gardener learns that weed barriers defy logic, strangle plants, and decimate soil. Weed seeds largely move by air or animal and are deposited in the mulch or organic material on top of the weed barrier – mulch which doesn’t decompose as it should because the weed barrier doesn’t allow it to contact the soil.
Now to be fair, landscape fabric has its uses. If you install a new annual garden every year, it’s great. As you’ll be pulling up every plant and replacing the fabric yearly, it will serve its purpose. It’s also useful in commercial agriculture. But it’s less than useless in perennial gardens and can actually do a lot of damage to your plants and soil.
The facts about landscape fabric weed barriers:
Weed barrier fabrics were developed for agricultural use, meant to be used for one season only. In fields, the fabric is placed on top of the soil and the plants are installed through them, with an ample cutout so the plant can receive enough water and fertilization. Nothing is placed on top of the fabric so that water, fertilization, air, and gas exchange can take place. The fabric is the mulch.
However, in home gardens, perennial plant roots, especially roots of large shrubs and trees , frequently become entangled in the fabric. I’ve seen it often during renovations – roots spread across the top of the fabric or become entwined in it, and not underneath it in the soil as they should (that pesky mother nature foils the best laid plans). The root systems of healthy trees and shrubs must grow at least as wide as their drip line, but weed barriers restrict this growth. The lack of deep penetrating roots make the tree or shrub easily toppled by high winds and very susceptible to drought. These pics from the University of Florida Extension service illustrate how landscape fabric girdles tree roots.
Tough weeds most definitely will grow through these fabrics. Anyone who gardens where the mighty Canadian Thistle grows will agree – I’m convinced that thistle will grow through steel.
Landscape fabrics will suppress below-the-fabric weed seeds the first season, but airborne seeds which settle in organic mulch atop the fabric will germinate, and some will root. As the mulch level increases, and organic decomposition occurs, more opportunity for rooting of weed seeds exists. Grasses like Nutsedge are a real problem – it will easily push through the fabric and the “nuts” (tubers) which are attached to the roots are virtually impossible to remove when growing underneath the weed barrier. And if you don’t get the entire nutsedge out, you get more nutsedge.
Many of the old fabrics aren’t very permeable, if at all. I’ve frequently seen soil beneath and above these weed barriers dry as a bone and compacted hard as cement, the color of baked clay. The plants were starving for nutrients and struggling to find water, slowly dying, even with layers of compost and mulch on top. And with no water penetration, little soil food web activity takes place, which one notes immediately by a distinct lack of worms and insect life. Conversely, when used in very wet or soggy areas, the weed barrier can trap water beneath it, creating a swampy mess.
Weed barriers separate the soil from the mulch and don’t allow proper biological activity and drainage to take place. Mulch, compost, and anything else you place on top of the soil requires actual contact with the soil to properly decompose. No decomposition means no humic acids to feed the plants.
I never asked one, but earthworms HATE landscape fabric. Worms eat organic material, which they can’t reach through the fabric, and they can’t poke their heads above the soil for air. So they leave. I have yet to see more than a few stray worms in soil underneath these fabrics.
Aesthetically speaking, when the fabric is exposed, it looks just awful – horrendous, ghastly, dreadful. Did I mention how bad it looks when the mulch slides off?
Planting bulbs through landscape fabric is a pain. Animals which do their work below ground like gophers can sometimes push bulbs off your mark and if they do, there’s little chance that tulip is going to be able to push through the barrier in spring. And if you’re cutting holes in the weed barrier, you’re also allowing air, water and sunlight to get at weed seeds, so what’s the point?
Good luck dividing plants like geraniums and irises.
Bad landscapers plant shrubs and trees with landscape fabric wrapped around the rootball. I suppose they believe that the roots will grow through the material. They’re wrong. Roots will wrap around themselves inside the material until the plant basically strangles itself.
So why do so many companies sell landscape fabric? Because it seems like such a good idea and so many home gardeners and bad landscapers keep buying it. Accept the fact that there is no magic weed barrier (say it out loud, it’s liberating). Any mulch applied heavily enough will do a far superior job to landscape fabric: stones, pea gravel, wood chips, or yard waste. Layer it 2-3″ thick, with black and white newspaper or corrugated cardboard beneath it, and very few weeds will get through it.
The best weed suppression is achieved by planting low-growing ground covers like yarrow, sedum, coreopsis, verbena, sage, juniper, bergenia, geranium, coral bells, phlox, vinca, or carpet bugle. Ground covers easily out-compete weeds in your garden and mature groundcovers also cut down on the expense of buying and hauling mulch every year. See this list from Colorado State University Extension of ground covers for any type of garden.
Garden Tip: For those who have trouble bending to pull weeds, invest a few dollars in a stirrup hoe, which will save your back and make weeding a breeze.