Landscape fabric, often called a weed barrier cloth, is a synthetic or woven material placed over soil to suppress unwanted plant growth. When applied correctly, this material can definitively kill grass, as this is one of its intended functions. The fabric works by forming a physical boundary between the soil and the atmosphere, eliminating the conditions required for turf and weeds to survive.
The Mechanism of Grass Suppression
The primary way landscape fabric kills grass is by inducing complete light deprivation across the covered area. Grass plants depend on sunlight to perform photosynthesis, converting light energy into chemical energy for growth. By blocking nearly all incoming light, the fabric halts this energy production, causing the grass to deplete stored carbohydrate reserves in its roots and eventually die.
Smothering the turf also severely restricts the exchange of gases between the soil and the air. While most fabrics are porous to allow some water to pass, they create a dense physical barrier that limits oxygen availability to the roots and soil microorganisms. This restriction can contribute to anaerobic conditions in the soil immediately beneath the barrier, further stressing and weakening the grass roots.
The physical weight and pressure of the fabric, especially when covered with a layer of mulch or stone, also contributes to the smothering effect. This combination prevents new shoots from successfully pushing through the soil surface and the fabric’s tight weave. Over several weeks to a few months, depending on the grass type and climate, the turf is completely killed and its root system is depleted of energy reserves.
Proper Applications for Landscape Fabric
Although landscape fabric is effective at killing grass, its most appropriate use is not necessarily in garden beds where soil health is important. The material excels in applications where its primary role is to stabilize aggregate materials and minimize weed growth in permanent, non-planted areas. This includes using the fabric as a sub-layer beneath gravel walkways, patios, or paver installations.
In these hardscaping projects, the fabric prevents the sub-base material, such as sand or gravel, from sinking into the underlying soil over time. It also acts as a barrier to stop the soil from migrating upward into the aggregate, which would otherwise create a medium for weeds to germinate in the stone layer. For these uses, a thick, non-woven geotextile fabric is often preferred for its strength and durability.
The fabric can also be used effectively in permanent ornamental beds that contain only mature trees and shrubs, particularly if the area is not expected to change or be replanted. Here, it is laid around existing trunks and stems and covered with a thick layer of inorganic mulch, such as river rock. This application reduces competition for water and nutrients from weeds without impacting the established root systems of the larger woody plants.
Common Problems and Maintenance Issues
While landscape fabric provides initial weed suppression, it frequently leads to long-term maintenance issues. The most common failure is the eventual growth of new weeds directly on top of the fabric itself. Airborne seeds and decomposing organic debris, like fallen leaves and dust, collect on the fabric’s surface and create a thin layer of fertile topsoil.
Once weeds establish roots in this debris layer, they often anchor themselves directly into the fabric’s weave, making manual removal extremely difficult. Pulling these weeds can cause the fabric to shred or tear, compromising the barrier and creating openings for weeds from below to emerge. The presence of the barrier significantly degrades soil health over time.
The fabric prevents the natural incorporation of organic matter, such as compost and decomposing mulch, from reaching the soil beneath. This leads to reduced activity from beneficial organisms like earthworms, which are responsible for aerating the soil. Over several years, the soil below the fabric can become hard, compacted, and nutrient-poor, inhibiting healthy plant growth.
The fabric itself is a synthetic material that eventually degrades due to exposure to sun and temperature fluctuations. As it breaks down, it becomes brittle and tears apart into pieces, making the eventual task of removing the tattered material labor-intensive. The difficulty of removing old, degraded fabric makes it a poor choice for any area where the landscape design may change in the future.
Alternatives to Fabric for Weed Control
Gardeners seeking effective weed control without the long-term drawbacks of synthetic fabric have several organic alternatives available. One effective method is the application of a deep layer of organic mulch, such as wood chips, shredded bark, or shredded leaves. A layer maintained at three to four inches deep suppresses most annual weeds by blocking sunlight while simultaneously enriching the soil beneath as it decomposes.
Another successful technique is sheet mulching, often referred to as lasagna gardening, which utilizes a temporary biodegradable barrier. This involves laying down overlapping layers of corrugated cardboard or several sheets of newspaper directly over the grass or weeds. The material is thoroughly soaked with water and then covered with a thick layer of compost or organic mulch.
The cardboard or newspaper effectively smothers the existing vegetation by blocking light, similar to the fabric, but it slowly decomposes to feed the soil instead of creating a synthetic barrier. This method improves soil structure and attracts earthworms, making it an excellent choice for converting a grassy area into a garden bed. For low-maintenance areas, planting dense, spreading ground cover plants is a biological solution that shades the soil and physically outcompetes weeds for resources.