The Landscape Fabric Weed Barrier Myth

© Provided by Big Blog Of Gardening Will landscape fabric suppress weeds in your garden for years? No. It's one of the great gardening myths of all time.

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.

“Weed barrier.”

“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. It was developed for use in commercial agriculture and it’s highly effective in that capacity. But it’s less than useless in perennial home gardens and can actually do a lot of damage to your plants and soil.

The facts about landscape fabric as weed barriers

Weed barriers were developed for agricultural use, meant to be used for one season only.

In agricultural fields, especially those tended by hand, weed fabric is placed on top of the soil and the plants are installed through it, 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 in effect a mulch.

In home gardens, plant roots, especially of large shrubs and trees, become entangled in landscape fabric.

I’ve seen it often during renovations – roots of perennials spread across the top of the landscape fabric just below the soil surface or become entwined in the weed barrier. As a result, the roots don’t grow deep in the soil as they should. The root systems of healthy trees and shrubs must grow at least as wide as their drip line, and usually a few feet deep, but weed barriers restrict this growth. The lack of deeply 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 weed fabrics.

Anyone who gardens where the mighty Canadian Thistle grows will agree – I’m convinced that thistle will grow through steel.

Landscape fabrics suppress below-the-fabric weed seeds the first season

…but seeds that later settle in mulch atop the fabric will germinate, and some will root. As the mulch level increases atop the weed fabric, and organic decomposition occurs, more opportunity for the 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.

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Many of the old weed fabrics aren’t water and gas permeable.

I’ve frequently seen soil beneath and above old weed fabrics dry as a bone and compacted hard as cement, the color of baked clay. The shrubs and flowers were starving for nutrients and struggling to find water, slowly dying, even with layers of compost and mulch on top. And with little to no water penetration into the soil, or gas exchange at the surface, little soil food web activity takes place, which is immediately apparent by the distinct lack of earthworms and insects just below the surface. 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 for proper biological activity and drainage.

Mulch, compost, and anything else you place on top of the soil require actual contact with the soil to properly decompose. No decomposition means mulch gets moldy and becomes home to mice and other small rodents. And without decomposition there’s a lack of humic acids to feed the plants, insects, and microbial life.

Do weed barriers decompose?

I have unearthed nearly intact weed barriers more than 20 years after they were placed in a garden. So no, they don’t decompose in the time it would take for a material like burlap to decompose. In fact, many are guaranteed not to decompose for 25 years.

I never asked one, but I bet earthworms HATE landscape fabric.

Earthworms eat organic material, which they can’t reach through the weed fabric, so they crawl away in search of food. I have yet to see more than a few stray worms in garden soil underneath landscape fabric.

Aesthetically speaking, when the weed fabric is exposed, it looks just awful – horrendous, ghastly, dreadful.

Did I mention how bad it looks when the mulch slides off?

Planting flower bulbs through landscape fabric is a pain.

To plant bulbs, you must cut a hole in the landscape fabric and plant it in the soil beneath. But animals that do their work below ground like gophers can sometimes push flower bulbs off the mark. If they do, there’s no chance that tulip or daffodil is going to grow through the weed barrier. 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.

If you’ve tried, you know what I mean. What a royal mess. Most of the time, plants tangled in the weed fabric are a total loss.

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, and it becomes rootbound.

So why do so many companies sell landscape fabric?

Because: a) it definitely has its uses in agriculture and b) it seems like such a good idea and so many home gardeners and bad landscapers keep buying it. 

As a gardener you have to accept the fact that there is no magic weed barrier (say it out loud, it’s liberating). Any mulch will do a far superior job to landscape fabric: stones, pea gravel, arborist wood chips, or yard waste. Layer it 2-3″ thick and very few weeds will get through it.

The best weed suppression and soil health is achieved by planting low-growing, native plants, especially ground covers. They easily out-compete weeds and cut down on the expense of buying and hauling mulch every year.

Sources: The landscape fabric myth from Linda Chalker-Scott, Ph.D., Horticulturist and Associate Professor, Washington State University;  Why I Hate Landscape Fabric, from North Coast Gardening; Garden myths: Landscape fabric-weed barrier cloth.

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