The Myth of Weed-free Landscaping

Today I’m revisiting a topic I first talked about back in 2013. I normally don’t do this, as I assume you can go back and reread whatever you’d like, using the options at in the sidebar at right. However, this is an issue that I think needs a lot more attention. I’m so frustrated, I could scream.

What is this horrific landscaping practice that makes me cringe? Landscape fabric.

Yes, too many people are drinking the landscape fabric Kool-ade, and I wince every time it see it. For the record, landscape fabric was designed to prevent dirt from washing through a stacked rock wall. It was never intended to be used to keep weeds from growing.

Perhaps that is why it doesn’t work.

Six years ago I pointed you to an article my friend Carey wrote and posted on Pikes Peak Area Garden Help, a blog started by some former El Paso County master gardeners. Her article is excellent; if you haven’t read it, please do so now: Landscape Fabric: Why you probably don’t need or want it.

In the intervening years, I’ve paid a lot of attention to the effects of this pernicious barrier on the plants and weeds, and I have some points to add.

First of all, Carey talks about how landscape fabric isn’t as permeable as we’ve been told. True, some air and water does get through the fabric—at first. But as dirt and silt fill these gaps in the weave, they clog. Pretty soon, the plant roots under the fabric are left without air or water, and the plants suffer. (This is the same problem as using black plastic under mulches.)

Colorado soils are notoriously low in organic matter. Ideally, decomposing compost should make up about 5%, and mineral matter 95%, but our arid and less-than-hospitable climate brings that percentage down to less than 1%. Once we’ve established a permanent landscape, we can’t be constantly digging in more amendments, so the only option is to layer an organic mulch on top of the soil. As it breaks down, it’s slowly incorporated into the soil, replacing that lost to further decomposition. Landscape fabric keeps the mulch from touching the soil, halting this natural process of regeneration.

While our expensive trees and shrubs wither and die, the weeds flourish. That’s one reason we consider them weeds—they’re often more persistent than whatever plants we actually want to grow. Yes, the fabric prevents the seeds underneath from germinating, but it in no way stops new seeds from blowing in. Over time, the dirt and silt that render the fabric impermeable also provide a lovely seed bed. Once the weeds have germinated, their roots grow through the fabric, making them nearly impossible to pull out. If you do manage to loosen that weed, the fabric often comes with it.

Actually, just the presence of several inches of mulch defeats most weeds. Typically, their seeds won’t germinate unless exposed to the light—a helpful trait if you want to sprout where there isn’t any competition from neighboring plants. So yes, please mulch. Just don’t use fabric underneath!

 Carey’s final point is that landscape fabric rarely stays hidden under the mulch on top of it. Wind, downpours, and foot traffic all serve to move the mulch, which slides easily on the slick fabric. And isn’t that bare spot lovely?

Lately, my gardening forums have been full of people complaining that their plants aren’t thriving. Some judicious digging reveals a layer of old landscape fabric, sometimes as much as a foot deep. Then they complain a lot louder when they realize they’ll need to remove it if they want their garden to be healthy.

Today I watched while a professional crew installed a new landscape at a house that was just completed down our street. Sure enough, they laid out the lawn, then shrouded every other inch of dirt in a layer of black fabric. I assume they’ll cut a hole for each plant, then cover the rest with rock. I had to fight the urge to run down and warn them.

But in fact, they’re just following the rules. Our HOA mandates the use of landscape fabric, and we all have to do whatever the HOA says, right? But I figure that they’ll never peek under all our shredded bark to see if our dirt is dressed—or not. Shhh… If you don’t tell them—we won’t.

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