Ground cover refers to any low-growing plant or material spread across the soil surface to provide coverage. The primary function of a ground cover is to compete with and suppress the growth of unwanted plants. Selecting the right material, whether living or non-living, depends on understanding how each option works and preparing the planting area correctly. Long-term weed prevention requires a combination of thorough site preparation and the strategic application of a dense cover.
How Ground Covers Prevent Weed Growth
Ground covers successfully suppress weeds through two main scientific principles: light deprivation and resource competition. Blocking sunlight is the most immediate and physical mechanism of action. A dense layer of material or foliage prevents the light required for photosynthesis and halts the germination of weed seeds lying dormant in the soil seed bank.
For living ground covers, the mechanism extends to direct biological competition. Once established, these plants create a thick root and canopy system that actively competes with weed seedlings for limited resources. This biological interference involves the uptake of water and nutrients, particularly nitrogen, before nearby weeds can access them.
Certain plant species, known as allelopathic covers, also employ a chemical defense. They release compounds through their roots or decomposing leaves that inhibit the growth of surrounding plants, specifically suppressing the germination and development of weed seeds. This combination of shading, resource competition, and chemical deterrence makes ground cover a multilayered defense against unwanted growth.
Best Living Plant Covers for Suppression
Effective living ground covers have a dense growth habit, rapid spread rate, and low stature, creating a thick mat that prevents light from reaching the soil. Vinca minor (periwinkle) is an excellent choice for shaded areas where other plants struggle. Its trailing vines form a dense, evergreen carpet that effectively chokes out weeds, though its vigorous nature requires occasional pruning to control its spread.
For sunny, well-drained locations, creeping thyme (Thymus serpyllum) forms a durable, fragrant mat. While it establishes slowly in its first year, it sends out stems that root as they spread, quickly forming a dense cushion that tolerates light foot traffic. Varieties like ‘Elfin’ thyme are particularly valued for their tight growth habit, which enhances their weed-smothering capability.
Creeping sedum, a succulent known as stonecrop, is ideal for hot, dry environments with poor soil, such as rock gardens or slopes. Low-growing varieties like ‘John Creech’ or ‘Red Carpet’ create a heavy cover of fleshy leaves that block sunlight and fill in open spaces where weeds would typically germinate. Selecting a ground cover appropriate for the site’s sun and soil conditions is paramount, as a struggling plant will not form the dense cover required for effective weed suppression.
High-Performance Non-Living Materials
Non-living materials offer an immediate physical barrier, providing a different approach to long-term weed control. Organic mulches, such as shredded bark or wood chips, decompose over time and add valuable organic matter to the soil. For effective weed suppression, these mulches must be applied at a depth of 2 to 4 inches, with a minimum of 3 inches often recommended for initial applications to block light.
Inorganic mulches, including stone, gravel, or rubber chips, offer much greater longevity because they do not break down. However, they do not enrich the soil and often require the installation of a non-degrading barrier underneath them. This barrier prevents the inorganic material from sinking into the subsoil over time, which would otherwise allow weeds to germinate directly in the stone layer.
Landscape fabric, a synthetic barrier, is highly effective at preventing weeds from emerging from the soil beneath it. However, failure occurs when organic debris accumulates on top, creating a thin soil medium that allows wind-blown weed seeds to germinate and root directly through the permeable fabric. Consequently, landscape fabric is often best used in conjunction with non-decomposing inorganic mulches or in hardscaping projects like pathways.
Preparing the Site for Long-Term Effectiveness
The success of any ground cover, whether living or non-living, depends on thorough site preparation. The primary cause of failure is attempting to cover existing weeds, particularly aggressive perennial types. Therefore, the first step involves the deep removal of all existing vegetation, ensuring that all roots and rhizomes are extracted to prevent regrowth.
For areas heavily infested with dormant weed seeds, a non-chemical method like solarization can be employed. This involves covering the moistened, cleared soil with clear plastic sheeting for four to six weeks, which traps solar energy and heats the topsoil to temperatures between 100 and 140 degrees Fahrenheit, killing many weed seeds and pathogens.
Before planting or mulching, the soil structure should be improved by incorporating organic matter, such as compost, into the top 6 to 8 inches. This amendment improves water retention and aeration, supporting the rapid establishment of desirable ground cover plants so they can outcompete any new weeds.
Finally, installing a clear boundary is necessary to contain materials like mulch and prevent aggressive living covers from invading adjacent lawn areas. This boundary can be created using metal edging or pavers sunk into the ground.