Whether you are starting a new garden bed or trying to control weeds in an existing bed, covering the bed in plastic is a quick way to clear the bed with minimal labor. Black plastic mulch also warms the soil, allowing you to plant in the garden bed sooner in spring. The mulch is left on the bed throughout the gardening season, preventing new weed growth amongst your plants. Apply mulch on new beds in fall to prevent weed seeds from germinating in late winter and spring. For existing beds apply the mulch prior to planting.
Remove visible weeds and garden debris from the bed. Till the soil to a 12 inch depth with a power tiller and work in any compost or fertilizer desired in the bed.
Lay black plastic over the entire bed. Push it down so it has contact with the soil in all spots.
Cover the edges of the plastic with 2 inches of soil to prevent it from blowing up. Alternately, lay landscaping rocks along the edges to hold the plastic down.
Cut a 3- to 6-inch holes in the plastic. Plant your vegetable or ornamental plants in the holes at the same depth they were at in their nursery containers.
Water the plants at the base, ensuring that the water gets into the gap between the plant and the plastic. If standing water is present on top the plastic after rainfall, poke small holes in the area with standing water to allow the water to drain under the plastic.
Cover the plastic with a 1-inch layer of organic mulch, such as straw or wood chips, during the heat of summer unless you are growing heat-loving vegetables such as peppers, tomatoes or melon. The organic mulch prevents the plastic from overheating the soil and damaging your desired plants.