Weed Mats are a Weed!
Why Weed Barrier Fabric is a Weed
Weed barrier fabric, typically a tightly woven, mesh-like material sold in rolls, was once hoped to be a miracle solution for reducing weeds. Initially, it works well, but by the second season, its effectiveness diminishes as weed seeds can still blow in, settle on top of the fabric in the mulch, and eventually germinate. Once this happens, the fabric’s effectiveness continues to decline each season.
Over the past few years, we have been removing the fabric, and it’s proven to be quite a challenge to eliminate it so we can restore the soils in those areas to health. We hope this article helps you avoid this pitfall in planting beds or, if it is already existing in your landscape, shows you why and how to correct the problem. There are places weed barrier fabric is useful in the landscape—just not in planting beds.
Reasons NOT to Use Weed Barrier Fabric
Reason 1: It Doesn’t Work
Weed barrier fabric doesn’t achieve its stated goal of holding down weeds. While it may work reasonably well for the first year or two, after that, weed seeds will establish on top of the fabric, and you will no longer notice any difference. Once those weeds start sprouting, their roots can get tangled in the fabric, making them even harder to remove and causing a more difficult weed situation than if you didn’t have the fabric in place at all.
Reason 2: It Kills Your Soil
The fabric prevents organic matter from getting into the soil, making it uninhabitable for worms and beneficial microorganisms. These organisms break down and incorporate organic matter into the soil, aerate the soil, and help with water penetration. Without them, the soil becomes barren, compacted, and dry. This lack of natural nutrients forces the use of artificial fertilizers. The compacted soil also forces roots to stay on the surface, making them less resilient to drought as water runs off the surface instead of penetrating the earth.
Reason 3: It Kills Your Plants
The standard way to use weed fabric is to lay it down and cut holes where the trees, shrubs, or flowers go. However, unless you enlarge the holes every year, the plants can outgrow the holes quickly. Trees can become girdled and die as they outgrow these holes. Flowers may spread on top of the fabric instead of in the soil beneath, making them less healthy and restricting their growth potential.
What To Do Instead?
Instead of weed barrier fabric, use a heavy coat of organic mulch 2-4” deep. The depth of mulch needed depends on the material used. Small, fine particle mulches like compost or "soil pep" are dense and block out light effectively, so 2-3" is sufficient. Shredded bark has larger chunks that can let light through, so using 3-4" is best.
Organic mulch breaks down and provides nutrients to the soil over time. Top dressing with a light coat of mulch (1”) in subsequent years keeps the mulch depth consistent and maintains its benefits. When organic mulch is used, your soil continuously improves as the organic matter and nutrients it contains work their way through the soil, feeding both plants and the beneficial life in the soil itself. Over time, your soil becomes better and better, unlike the decline experienced beneath weed barrier fabric.
When WOULD You Use Weed Barrier Fabric?
Despite its failure to work as intended in planting beds, weed barrier fabric is still useful in certain landscape situations. It’s our preferred fabric to use beneath gravel, decomposed granite (or similar), or other inorganic permeable materials used for informal landscape paths. The fabric keeps the gravel from being absorbed into the soil and helps keep the path intact. It is best used beneath inorganic materials like gravel that have some heft and weight. When used beneath mulch, the slick surface of the fabric makes it too easy for the wind to lift the mulch off the path.
