Landscape fabric is a permeable material designed to create a barrier between the soil and the surface material, primarily to suppress weed growth and stabilize the substrate beneath hardscaping elements. This material allows water and air to pass through to the soil below, preventing weeds from accessing sunlight and germinating. While doubling the material might seem like a simple solution for better protection, installing two layers of fabric is only beneficial in specific, high-stress circumstances.
Specific Scenarios Justifying Double Layering
Layering fabric is a justifiable strategy when dealing with aggressive perennial weeds that are known to push through single barriers. Weeds like Bermuda grass or nut-sedge utilize strong rhizomes or tubers that can pierce or grow around a standard single layer of fabric. The doubled thickness provides a more formidable physical barrier against these persistent root systems.
Another scenario that warrants a layered approach is beneath load-bearing structures or high-traffic areas, such as walkways, patios, or paver installations. The fabric acts as a separator, preventing the underlying soil from migrating up and mixing with the gravel sub-base. Using two layers of a heavy-duty, woven geotextile fabric increases the system’s tensile strength and overall durability against shifting soil and heavy compression. This added strength helps maintain the integrity and levelness of the hardscape over a longer period.
Practical Drawbacks of Using Two Layers
Despite the perceived benefits, doubling the fabric introduces problems concerning the health of the underlying soil and long-term maintenance. The most immediate issue is a reduction in water percolation and gas exchange, which leads to poor soil conditions. Stacking layers blocks the microscopic pores, slowing the movement of water and oxygen down to the soil. This reduced drainage can cause water to pool above the upper layer, potentially leading to soggy mulch or root rot in nearby plants.
Over time, this anaerobic environment can suffocate beneficial soil organisms, such as earthworms, which are responsible for natural soil aeration and nutrient cycling. A common consequence is the creation of a new weed seedbed directly on top of the fabric. Fine debris, dust, and decomposed organic matter inevitably settle onto the top layer. This accumulation forms a shallow, nutrient-rich layer of soil above the barrier, allowing new weed seeds to germinate and establish roots.
Once weeds take root in this shallow layer, their root systems often intertwine with the woven fibers, making hand-pulling nearly impossible without tearing the material. The increased cost of material and the doubling of installation labor make the practice inefficient for most standard landscaping applications. Consequently, the double-layer system often fails within a few years, leaving a matted, difficult-to-remove mess that requires remediation.
Essential Installation Steps for Layered Fabric
When site conditions require two layers, careful installation is necessary to maximize effectiveness and minimize drawbacks. Begin by ensuring the ground is clear of debris, weeds, and sharp objects that could puncture the material. The soil should be graded to promote positive drainage away from any structures before the first layer is unrolled.
Lay the first layer of fabric, securing it with landscape staples along the seams and perimeter, ensuring a minimum overlap of 6 to 12 inches where the edges meet. The second layer is positioned directly on top of the first, but its seams must be offset or staggered from the seams of the bottom layer. This staggering prevents a continuous line of weakness where aggressive weeds could penetrate both layers.
To maintain the integrity of the barrier, use an increased number of metal pins, driving them through both layers and securely into the soil below. Since the layers are prone to shifting due to increased friction, a dense pinning pattern is necessary to keep the entire system from sliding. Finally, the double-layered system must be immediately covered with a minimum of two to three inches of mulch or gravel to protect the fabric from ultraviolet degradation and to help anchor it.