Whether grass must be physically dug up before mulching depends on the project’s timeline and the type of grass being removed. Mulching involves covering a ground area with material to suppress weeds, conserve soil moisture, and improve aesthetics. When converting a lawn into a mulched garden bed, gardeners typically choose between two preparation methods: direct removal or smothering. Both approaches successfully eliminate existing turf but differ significantly in the labor and time required to complete the project.
The Direct Removal Method
The direct removal method involves physically lifting the sod and grass from the ground. This traditional technique uses a sharp flat spade to cut and peel away the turf or a specialized machine called a sod cutter to slice the grass roots just beneath the surface. This method provides an immediate, clean, grass-free base ready for mulching and planting.
Complete removal prevents the existing grass from regenerating through the new mulch layer. This makes it the preferred method when dealing with highly invasive grasses, such as Bermuda grass or quackgrass, which possess tenacious underground root systems called rhizomes. The major drawback is the intensive physical labor required for large areas and the subsequent problem of disposing of the removed sod and soil. After removal, the soil may still require tilling or raking to loosen it and remove any remaining root fragments before the final layer of mulch is applied.
Grass Smothering Techniques
The alternative to intensive labor is the “no-dig” approach, often called sheet mulching or lasagna gardening, which kills the grass in place. This technique deprives the grass of light and air, halting photosynthesis and causing the vegetation to die back. A key benefit is that the killed grass and applied layers decompose over time, adding valuable organic matter and improving soil structure.
Smothering begins by mowing the existing grass to the lowest setting possible. Next, a barrier layer of overlapping cardboard or several layers of newspaper is laid directly over the area. Care must be taken to remove any plastic tape or glossy paper sections from the barrier material.
The barrier must be thoroughly soaked with water and overlapped by at least six inches at the seams to ensure no light penetration. A final layer of organic mulch, such as wood chips or compost, is then spread over the barrier to a thickness of four to six inches. This top layer holds the barrier in place, insulates the soil, and aids decomposition. The main requirement for smothering is patience; a typical waiting period of six to eight weeks, or even several months, is needed before the area is ready for planting.
Choosing Mulch Based on Application
The preparation method heavily influences the characteristics required for the final mulch material. If you choose the direct removal method, the underlying soil is bare. Mulch selection can focus primarily on aesthetics, soil temperature regulation, and moisture retention. Coarser mulches like shredded bark or wood chips are excellent choices for their longevity and ability to suppress new weeds from germinating.
When using smothering techniques, the mulch material must serve a dual purpose: it must be dense enough to block light and heavy enough to hold down the barrier. Therefore, a substantial layer of wood chips, compost, or a combination of materials works best for the top layer. Inorganic mulches, such as rock or rubber, are not recommended for smothering projects because they do not decompose to enrich the soil and lack the density required to securely anchor the biodegradable barrier layer underneath.