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New Landscape Fabric in a Tree Lawn

Homeowners are being sold acres and acres of landscape fabric in our area this spring. Maybe they are looking for an easy way to cover their landscape in a year with watering restrictions, figuring that a no-water-needed configuration of landscape fabric and mulch is the best alternative to turf. Or maybe they’ve just been fighting weeds in an area for so long that just covering it with something seems the ideal solution.

Landscape fabric comes in a seemingly endless variety of weights, thicknesses, and synthetic materials (mostly plastic). Sometimes it is called weed barrier or weed blocking fabric. After moving into my house over twenty years ago, I discovered what was probably the original “weed-blocking” fabric, a layer of black plastic bags under river rock in my tree lawn (the area between the sidewalk and street). Edges of the plastic showed between rocks, and big tall weeds thrived! Once we decided to remove the rock-and-plastic landscaping, just under the plastic we found a layer of roots from the green ash tree that lives in the tree lawn. The soil was bone dry, and the roots were doing their best to search for needed water.

In modern landscape fabrics, thicker plastic is one of the options available. Some are completely nonpermeable, while others claim to have channels to allow “air, water, and nutrients” to penetrate. They are not made from recycled materials and usually are not recyclable. Other more permeable options are available, usually being made of polyester (some products do not even say what they are made of!). These are somewhat see-through and may stretch a bit when tugged.

The marketing for these fabrics promise attractive, weed-free landscapes. In truth, it is not long before dust, soil, and fine mulch debris accumulate on top of the fabrics, creating a perfect seedbed for any weed seeds that blow in. Additionally, the fabrics create a perfect, smooth runway for mulch to blow off of in high winds or to run off of in heavy rain. Rarely do I see a landscape fabric-and-mulch area that doesn’t have patches of the fabric showing through or edges of the fabric rippling above the mulch.

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New (Less than a Month Old) Landscape Fabric and Mulch Installation

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Older Landscape Fabric and Mulch Installation

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Landscape Fabric Showing Through Rock Mulch

Colorado State University Extension absolutely does not recommend polyethylene landscape fabric. Even those plastic fabrics that claim to have a system to allow some water and air through don’t let enough through to prevent run-off in a heavy rain, and they don’t allow surrounding trees to receive enough water. Additionally, CSU doesn’t recommend landscape fabric under organic (like wood chip) mulch because the mulch will stay in place better if it is in direct contact with the soil (although homeowners will have trouble keeping wood chip mulch in place in high wind areas, regardless of whether landscape fabric is used under it). Also, organic mulch can slowly break down and add organic material to the soil if there is no barrier between the two. They suggest that if an area is mulched and weeds are still a problem, the mulch is not deep enough. If a temporary weed barrier is needed in a newly cultivated or planted area, a two-to-three sheet layer of newspaper under a three-to-four inch layer of organic mulch is recommended since it will suppress weeds, and the newspaper will usually break down within a year. Cardboard is not recommended in our area because of the arid climate – it will be years before it breaks down and the soil underneath it will stay far to dry to support healthy microorganisms and to desirable plant roots, including tree roots.

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Impermeable Fabric Around Young Shrub

Unfortunately, this is another case of “if it seems to good to be true, it is.” Covering our ground with artificial materials just isn’t the best route to an attractive, low maintenance landscape. Start by eradicating the weeds that are already in the area you want to cover, cover with newspaper if you want a barrier, then cover with a thick layer of organic mulch (if the area is very windy, you may need to go with rock over bark or chip mulch). You’ll be happier in the long run than if you spend good money on fabrics that rip, show through the mulch, and encourage new weed seeds to germinate in a fairly short amount of time.

Contributed by Carey Harrington, Certified Colorado Gardener and Colorado Native Plant Master

References and Additional Resources:
CSU Extension Master Gardener Note #245, “Mulching with Wood/Bark Chips, Grass Clippings, and Rock” – www.cmg.colostate.edu/gardennotes/245.html

CSU Extension Fact Sheet #7.214, “Mulches for Home Grounds” – www.ext.colostate.edu/pubs/garden/07214.html

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