Landscape fabric. It’s what goes under the mulch. Right? I’ve had several conversations with home gardeners looking for a permanent solution to keeping the weeds down and each time I warn them about the use of landscape fabric.
If you’re thinking, “Hang on! Landscape fabric doesn’t work?” Of course, you’ve seen people on TV and perhaps watched professional landscapers roll out the black landscape fabric before spreading mulch. And why does every garden center sell the stuff if it doesn’t work?
The Scoop on Landscape Fabric
Here’s the thing: Landscape fabric does help to suppress weeds, but only for a couple of years. Additionally, over time it may actually do more harm than good to your plants. Let’s examine the background of landscape fabric and what’s happening under the mulch.
Landscape fabric was initially developed for the commercial world. Commercial vegetable growing and holding soil when building something structural like a retaining wall. The main selling points for landscape fabric are it is permeable, prevents weeds from growing, and is permanent. Let’s look at each of these points.
Permeability - At the store, landscape fabric usually can be found in two forms: 1) a woven fabric created by weaving thin strips of plastic and 2) a spun fabric created using polyester fibers. These landscape fabrics are somewhat porous in both cases, meaning they allow water and air to move through. Being porous is important as water and air are critical resources for plant roots.
You may have noticed I wrote “somewhat porous”. There different grades and thickness levels of landscape fabric that all affect porosity, but either way it still creates a restriction of water and air movement. And over time it has been demonstrated, landscape fabric pores will trap dirt and other sediments, making them even less permeable. In fact, I’ve pulled up landscape fabric after a deep soaking rain, only to find dry soil beneath.
Prevents weeds – Every time you disturb the soil, you create an opportunity for weed seeds to germinate. Those seeds are already in the soil waiting for the perfect conditions to sprout. When I go in to install a new landscape bed, there is a lot of soil disturbance occurring. There may be tilling. Bringing in amendments. Digging in new landscape lighting or irrigation. And of course, installing plants. One way to avoid that initial flush of weeds is to cover the soil. Yes, mulch can do the trick, but most people don’t put it on thick enough and the professionals can use less mulch if they add landscape fabric on top of the soil. The fabric suppresses the weeds for a couple of years, but eventually, new weed seeds blow into the landscape bed. Or a few particularly tenacious weeds manage to grow right through the fabric. If an organic mulch was installed on top of the landscape fabric, that begins to decompose, but cannot be incorporated into the native soil because of the fabric. Only after a few years, pulling a weed may also bring up sections of the fabric and you’ll be cursing the stuff!
Permanent – While most landscape fabrics are comprised of some type of plastic fiber, they are not permanent. Some cheaper fabrics will degrade in the soil, while others get pulled up by the gardener pulling up a weed. And if you like to plant lots of annuals in your landscape beds, you will wind up with Swiss cheese landscape fabric as you must cut holes to reach the soil beneath for the plant roots.
Are there alternatives to landscape fabric?
So what, if anything, can be used under the mulch? Here are few other alternatives to landscape fabrics:
Newspaper – Many homes have a pile of old newspapers and if not old papers can often be picked up at the newspaper printer. Some commercial garden suppliers are now offering newsprint in large rolls. A preference for using newspaper is that it is not permanent. The newsprint should decompose over time, so it shouldn’t become a barrier to planting say a flat of annuals. Use only a couple of sheets thick as too much newsprint could lead to an impermeable barrier. Avoid using glossy paper inserts.
Cardboard - Lots of gardeners use cardboard, but I would offer some words of caution with this material. Cardboard is often covered in tape, stickers, and other labels. These are coated in plastic, don’t decompose quickly, and often work their way to the surface. Some cardboards are also coated in wax or plastic material. This prevents water from moving to the soil. And plain cardboard can also act as a water barrier. I have used in my garden to smother weeds and when I’ve watered plants surrounded by cardboard, the majority of the water sheds off and doesn’t move into the soil beneath. This runoff is especially bad if the cardboard is dry. If you still plan to use cardboard, make sure it is not coated, remove any labels and staples, and cut a wide enough hole around your plants to make sure water can get through to the roots.
Plastic – Truly the wrong direction to take, but I see plastic sheets go down all the time under mulch. We really don’t need more plastic in the environment. Unless you’re building a pond, just steer clear of this stuff.
Wood Mulch – Yes, the very stuff you usually install on top of landscape fabric, just more of it. Up to six inches on new landscape beds can help suppress that first flush of weeds. Not all wood mulch is created equal. Shredded mulch fibers tend to knit together over time and create a shell that needs to be cultivated at least once per year. Large or coarse wood chips tend not to create a mulch shell and allow water and air to move into the soil. A lot more gardeners are utilizing arborist wood chips, which are typically chipped into coarse sizes and often free.
Good Growing Tip of the Week: I would be remiss to not mention rock mulch as something that often gets installed on top of landscape fabric. From a horticultural perspective, rock does not add any value to the plants, in fact, rock may create more inhospitable conditions. Some uses for rock mulch are if you’re growing an alpine rock garden, installing rock where plants won’t grow, or a bare spot to mix pesticides or place containers. I’ve also pushed enough wheelbarrows of granite gravel to be heavily biased against rock mulch.
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