By Jeff Floyd
Certified horticulturist and arborist
Ask any knowledgeable horticulturist how effective weed barrier fabric is in controlling weeds and you’ll likely hear that any advantages are outweighed by the shortcomings. However, most will acknowledge an unanticipated benefit when properly installed in a very specific location.
Weed fabric is a dark or neutral-colored material made of synthetic fibers which are woven into thin sheets. The sheets are four to six feet wide and up to three hundred feet long. The fabric is often rolled out in new flowerbeds or gardens and covered with mulch prior to installing plants. Advocates of weed fabric claim that the pores manufactured into the sheets are too small to permit weed growth but large enough to allow for the passage of air and water.
Unfortunately, the pores quickly become clogged by debris much the same way an air conditioner filter traps fine particles eventually limiting airflow. Research has established that weed fabrics also limit biological activity in the soil by modifying its normal interaction with the environment. The tiny growing tips of many weeds still manage to penetrate the pores and grow through the barrier within a year to a few short months. Often, the fabric will heave up above the mulch layer and create an unsightly mess. All this makes the fabric worse than useless.
However, the fabric serves a function of sorts when installed beneath inorganic mulches like those used in rock beds or in crushed granite pathways. In this scenario, there are no plants to be affected by reduced soil health. Here, the material will act as a barrier to keep the mulch from sinking and becoming a mixture of soil and rock. This keeps the path or rock bed intact longer, requiring less maintenance in the way of topdressing with additional mulch.
The key to successfully using weed fabric under rocks is that it must be pinned securely to the ground using sod staples that are at least six inches long and the material on top of the fabric must be at least four inches deep. However, as is the case where most weed fabric is planted, be prepared to eventually control weeds by hand removal or herbicides.
