Landscape fabric, a permeable barrier typically made from woven or non-woven synthetic fibers, is often considered when installing a new gravel surface. Gravel applications range from simple garden paths and decorative rock beds to heavily trafficked areas like patios and residential driveways. Understanding the primary functions of the fabric and its long-term performance is important before deciding whether to lay it beneath your aggregate layer.
Preventing Material Migration and Stabilizing the Base
The most significant and reliable function of landscape fabric under gravel relates to structural engineering, not horticulture. When heavy loads, such as vehicles or foot traffic, are applied to a gravel layer, the aggregate material is pressed downward into the underlying subsoil. This process, known as material migration, causes the gravel to sink and the native soil to contaminate the base layer.
Installing a high-quality geotextile fabric creates a separation layer that physically prevents the aggregate from mixing with the subsoil. This separation maintains the intended thickness of the gravel layer, reducing the need for frequent replenishment. For driveways or other areas subject to concentrated weight, the fabric also stabilizes the base by distributing the load across a wider area of the subgrade.
This reinforcement helps maintain the structural integrity of the surface and minimizes the formation of potholes or ruts over time. The fabric also permits water to drain through, preventing water from pooling and causing the subsoil to soften.
The Long-Term Reality of Weed Control
Many people choose to install landscape fabric primarily to suppress weeds, but its effectiveness as a long-term weed barrier is often overstated. The fabric works initially by blocking sunlight, which prevents weed seeds already in the soil from germinating and growing upward. However, the fabric cannot prevent airborne seeds or organic debris from settling on top of the gravel layer.
Over time, dust, decomposing leaves, and other organic matter accumulate in the spaces between the gravel pieces. This thin layer of organic material acts as a new germination medium, creating a fertile environment for new weeds to sprout directly above the fabric. Once established, the roots of these weeds grow downward and become entangled within the woven or non-woven structure of the fabric. This entanglement makes manual weeding extremely difficult, as pulling the weed often tears the fabric or leaves the root structure deeply embedded.
Soil particles can eventually clog the pores of the fabric, restricting the movement of air and water into the native soil beneath. This clogging can lead to reduced soil health and create conditions where weeds that can tolerate dry, compacted soil thrive. While the fabric may prevent weeds from growing up from below, it actively contributes to the problem of weeds growing on top, which is the more common long-term issue for gravel surfaces.
Situations Where Fabric Installation is Detrimental
While landscape fabric offers structural benefits, there are specific scenarios where its installation can be counterproductive, particularly in areas with high organic debris. Under large deciduous trees, for example, the constant fall of leaves and needles rapidly creates the top layer of organic matter that fuels weed growth, quickly negating the weed suppression benefit.
On sloped surfaces, the fabric can sometimes cause the gravel to become unstable. The smooth surface of a synthetic fabric may create a plane of slippage between the gravel and the subsoil, causing the entire aggregate layer to shift or slide down the incline, especially after heavy rain.
If the area is one where future planting is likely, the fabric creates a significant obstacle, as it must be cut away for every plant, leading to a patchwork barrier that is less effective and harder to maintain. Base stability may be better accomplished by using a deeper, highly compacted layer of crushed stone aggregate that naturally locks together.