Weed-kill:Geotextiles have major drawbacks

One of the longest-running battles in the history of gardening could be titled "Gardener vs. Weeds".

There are many compelling reasons to prevent, eradicate or at least control the weeds that seek to compete with our desired plantings. However, when the method of control is more harmful than the result obtained, such as in widespread applications of chemical herbicides, it is time to take a look at alternate practices to achieve our goals.

One of the more recent innovations in the war against weeds is the use of geotextile fabrics. A geotextile is typically defined as any permeable textile material (fabric) used to increase soil stability, provide erosion control or aid in drainage. Geotextiles have been in use for thousands of years dating back to the Egyptian pharaohs.

Commonly called landscape cloth or weed-barrier film, modern geotextiles are usually made from a synthetic polymer such as polypropylene, polyester, polyethylene or polyamide. Geotextiles can be woven, knitted or non-woven. Varying polymers and manufacturing processes result in an array of geotextiles suitable for a variety of civil construction applications.

The property of allowing water and air to pass through while preventing weeds from coming up through it make landscape cloth seem like an ideal solution for weed prevention. As a replacement for the use of polyethylene sheeting under bark, it appears to be a vast improvement.

Much of my work as a landscape contractor involves renovating existing landscapes that have either become overgrown, have been neglected, or are generally not thriving for various reasons. I have been involved with projects that have had landscape cloth and weed-barrier fabrics installed for differing lengths of time and in every case where I have encountered them, I have run into the same set of problems.

Raking off the covering and peeling the cloth back invariably reveals a dead, lifeless-looking and hard, compacted soil underneath. And this can take place in as little as a couple of years! Perhaps the most disheartening fact of all is seeing the trailing patterns made by earthworms as they tried and failed to find a way through the fabric.

I have several serious concerns about these cloths. The first is that although they are permeable, they seriously limit the infiltration of air and water into the soil, and that is a huge drawback. Organic mulches, if over-applied, also slow the passage of air into the soil, but their advantages greatly outweigh the negatives. The cloths are not UV-resistant and need to be covered to prevent solar degradation. In time, the finer particles of the mulch work their way into the surface of the cloth and fill in the pores, further impeding its porosity.

Planting through the cloth involves making slits in the material and getting dirt all over it, which is a hassle at best. Anything that stifles the desire to go out to plant or makes gardening less fun rates low in my book. As soon as dirt gets spread on the surface, weeds invariably begin to grow. And speaking of weeds, while the barriers do a good job of preventing annual weed seeds from growing through the cloth, they do not prevent weeds from sprouting and growing in the covering mulch. It seems that roots are able to grow quite well down through the cloth. If you have not killed tough perennial weeds beforehand, you may find you still have to deal with blackberries, dock and thistles.

The biggest drawback to using these products, in my opinion, is that they completely block the entry of organic matter into the soil. It effectively stops the assimilation of leaf debris, decomposing bark or a topdressing of compost into the soil. That alone would negate their use for me. Add in all the other factors and you won't see me applying them in my yard.

There are two cases where I will use them: as a liner under valve boxes to prevent soil from entering them and as an underlayment for large particle rock mulch, as in a dry streambed. Although attractive at first glance, I have found the use of geotextile cloths to be a disadvantage in most landscape applications.

Stan Mapolski, aka The Rogue Gardener, can be heard from 9-10 a.m. Saturday mornings on KMED 1440 AM and seen in periodic gardening segments for KTVL Channel 10 News. Reach him at stanpolski@gmail.com.

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