Black plastic mulch doesn't just spare you from weeds in the garden bed; it also can let you plant earlier in the spring. The black material absorbs the sun's heat, warming the soil beneath, bringing it to planting temperature up to two weeks ahead of uncovered soil. Most plastic mulch is too thin to hold up more than one season, so it's generaly used in vegetable or annual gardens. The plastic doesn't allow water through. It minimizes water loss from evaporation, but you must set up irrigation under the plastic.
Loosen the top 6 inches of soil by turning it over with a spade or working it with a power tiller. Turn in a 2-inch layer of compost, and add any fertilizers needed by the specific plants you plan to grow. Smooth the soil surface with a rake.
Lay drip-irrigation lines or a soaker hose down each planting row. Mark the locations of the lines with plant stakes set just outside the edge of the bed at the end of each irrigation row.
Spread the black plastic mulch over the bed. Cut it from the roll with a utility knife, so it fits the length of the bed. Continue to put down sheets of plastic until the bed is covered. Overlap the sheets by 4 to 6 inches, so the soil isn't exposed at the seams.
Insert a U-shaped garden staple into each corner of each plastic sheet to anchor them to the ground. Place additional staples around the perimeter of the plastic, spacing the staples about 8 inches apart. Install staples along each seam where sheets overlap, also spacing them 8 inches apart, so the plastic does not pull up.
Cut an X into the plastic for each each plant, using a utility knife. Make the cuts along the rows made by the irrigation hoses. Fold under the flaps formed by each X, and transplant your plants into the holes formed in the plastic by the cuts.