Black plastic mulch is readily available at garden centers and home improvement stores. The thin plastic serves many uses in both vegetable and ornamental flower beds. The mulch warms the soil, allowing for earlier planting. It also prevents weeds, and protects vegetables and fruits from fungus and disease in the soil. Plastic mulch also preserves soil moisture by inhibiting evaporation, though care must be taken so the soil doesn't dry out or become too moist under the mulch.
Prepare the garden bed in early spring. Remove dead plants, leaves and garden debris from the soil, then till it to at least a 10-inch depth to loosen the soil. Work in a 2-inch layer of compost and fertilizer recommended for the type of plants you are growing.
Mark the planting rows in the bed with twine or make shallow furrows with the tip of a hoe. Lay a drip-irrigation hose down the length of each marked row.
Level the top of the bed with a rake, then dig a 2-inch-deep trench along each edge of the bed. Place the soil in a wheelbarrow or on top of a tarp placed on the ground outside of the bed.
Lay the plastic mulch over the bed, pushing the edges into the trench you dug. Place the dirt from the wheelbarrow or tarp back into the trench to anchor down the plastic.
Cut planting holes in the plastic mulch along each irrigated row. Cut holes 3 to 6 inches in diameter, depending on the size of the plant stem.
Plant the transplants into the holes as recommended on the plant label or seed packet. Water from the top with a hose or a watering can immediately after planting to collapse any air pockets in the soil. Water with the drip hoses, according to water recommendations for each plant type.
Spread a 1-inch layer of organic mulch, such as wood chips, over the plastic mulch for ornamental flower beds. This disguises the plastic but still allows your garden to reap the benefits of it.