Converting a lawn into a garden bed or landscape area without strenuous digging or chemical herbicides can be achieved through sheet mulching. This process focuses on systematically layering organic materials directly over the existing turf to smother the grass by depriving it of light and air. This method utilizes decomposition to break down the turf over time, simultaneously improving the underlying soil structure.
Site Preparation and Material Selection
Begin by precisely marking the area designated for conversion using stakes, string, or landscaping paint. Before laying down any materials, the existing grass should be mown to the lowest possible setting. Reducing the height of the turf minimizes the energy reserves available to the plants and makes the smothering process more effective.
The most effective suppression layer is heavy-duty corrugated cardboard, as its density effectively blocks sunlight. If cardboard is unavailable, several layers of black-and-white newspaper can be used as an alternative barrier. Remove all plastic tapes, staples, and glossy labels from the cardboard before placement, as these synthetic materials do not decompose.
Selecting the material for the final, visible layer depends on the planned use for the area. For pathways, durable wood chips or bark mulch provide excellent weed suppression and longevity. If the area will become a planting bed, a mix of compost, shredded leaves, or aged manure can be layered directly on the barrier to quickly enrich the soil. This top layer serves an aesthetic purpose and helps retain moisture in the suppression layers beneath.
Creating the Grass-Suppressing Barrier
The success of sheet mulching relies on the technique used when laying the cardboard or newspaper barrier. Begin placing the chosen material directly over the mown turf, ensuring every piece overlaps the adjacent piece significantly. A minimum overlap of six to eight inches is recommended to prevent seams from becoming pathways for grass to grow toward the sunlight.
Once the barrier is fully laid across the area, it must be secured against wind and shifting. Placing small rocks, bricks, or a thin layer of soil can hold the cardboard firmly in place before subsequent layers are added. Immediately after securing, the entire barrier layer must be thoroughly saturated with water until it is pliable and damp. This wetting process initiates the breakdown of fibers and ensures the material stays in place, starting the decomposition.
Extend the cardboard barrier slightly beyond the final desired edge of the mulched area. This ensures that aggressive runners or rhizomes from the lawn boundary are also smothered. This extension provides a buffer zone, creating a cleaner transition between the old lawn and the new landscape feature.
Layering and Application of Mulch
If the area is intended for planting, begin applying intermediate organic matter after the cardboard is wetted. Spread a two-to-three-inch layer of nutrient-rich material, such as finished compost or aged leaf mold, directly onto the wet barrier. This layer introduces beneficial microbes and organic nutrients that filter down as the cardboard breaks down. This material speeds up decomposition and provides an immediate growth medium for new plantings.
The final step involves covering the entire layered structure with the chosen aesthetic mulch material, such as wood chips or shredded bark. The total depth of all layers above the cardboard should be between four and six inches for effective weed suppression and moisture retention. This depth helps regulate the soil temperature, providing insulation from extreme heat and cold. The thick covering also prevents weed seeds from germinating by blocking light.
When applying the final mulch layer, remember established surrounding plants, shrubs, or trees. Mulch should never be piled directly against the base or trunk of woody plants, a common mistake referred to as a “mulch volcano.” Keeping the mulch several inches away from the trunk prevents moisture buildup and subsequent rot or damage. The goal is to cover the ground surface, not the plant stems.
The newly mulched area should receive an initial deep watering to settle all the layers and encourage microbial activity. While the lawn is immediately smothered, the cardboard barrier takes time to fully decompose and integrate into the soil. For planting directly into the new bed, wait six to twelve weeks to allow the grass to die completely. During this waiting period, the dead turf grass contributes organic matter, leading to a richer soil structure for future gardening efforts.