WSU CAHNRS

Washington State University Extension

Garden Tips

Using Landscape Fabric

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

GARDEN TIPS – SEPTEMBER 19, 2014 – WHY NOT LANDSCAPE FABRIC?

When we moved to our new house seven years ago, I had the enjoyable task of starting our landscape from scratch. My plan included a variety of trees in the lawn and plenty of shrubs and ornamental grasses in landscape beds around the house and the perimeter of yard. Adamantly opposed to using landscape fabrics or ‘geotextiles,’ I mulched the beds with only a four inch layer of medium-size shredded bark after planting.

Admittedly, landscape fabrics or geotextiles are better than the black plastic used for mulching landscape beds in the 70s and 80s. The fabrics allow for the movement of air and water, where black plastic did not. Even though they do break down with time, fabrics covered with mulch last longer than black plastic in the same situations.

So why am I fervently against using landscape fabrics? To make landscape fabrics more aesthetically pleasing, they are often covered with a thin layer of mulch. Bark or wood chip mulches decompose with time, creating material in which weeds can grow. While rock mulches do not break down, blown in dust can create a layer of soil where weeds will also grow. Plus landscape fabrics do eventually degrade, especially when covered with only a thin layer of rock or bark mulch that does not block UV radiation well.

Many gardeners who have used landscape fabrics will tell you they are not a good solution to long-term weed control. Weeds will invade the beds and then the fabric becomes a nightmare, especially when Bermuda grass or field bindweed (wild morning glory) are involved. The roots or rhizomes of these trailing pernicious weeds find their way into the fabric fibers, making it impossible to rogue them out with pulling. If you do try to pull them out, the fabric comes with them. Arrrgh!

The best way to control weeds in landscape beds is with organic mulches. I prefer the look of shredded bark, but wood chips are just as effective and less expensive. Dr. Linda Chalker Scott, WSU Extension Horticulturist, prefers wood chips because of problems associated with shredded bark. She favors wood chips because of the possible contamination of bark with salts or weed seeds and because the sharp, pointed fibers of softwood bark cause tiny slivers in gardeners’ hands. In addition, bark mulch may resist water penetration because of the waxes and lignins contained in bark.

Whether you use bark or wood chips as a mulch, the layer should be 4-6 in thick. This blocks light from getting to the soil, preventing weed growth. The layer also helps retain soil moisture. I advise keeping mulch away from direct contact with the base of trees and shrubs. A thick layer of mulch touching a plant bases can lead to collar rot causing serious damage to trees and shrubs.

Chalker-Scott recommends applying a 8-12 in thick layer of wood chip mulch if you are trying to reclaim a landscape site with a serious perennial weed problem. She cautions you to taper down to a very shallow layer close to trees and shrubs.

Mulching with bark or wood chips is not a ‘place-it and forget-it’ situation. They both gradually decompose, adding organic matter to the soil. This is good. Periodically you will need to add fresh mulch on top of the old to maintain the weed controlling 4-6 in layer, being careful to keep the mulch away from the base of plants. By the way, fall is a great time to renew the bark or wood chips in your landscape.

Published: 10/9/2014 2:40 PM

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