Mulch is a material placed over soil to improve a garden's appearance. Mulches are commonly made out of materials such as bark, peat moss, pine needles, gravel or any material that may be spread uniformly over a large area. Mulch isn't for appearance only; it retains moisture in the garden soil as well as preventing the growth of new weeds by blocking out sunlight. Recycled black rubber is desirable because it is heavy and will not blow away.
Spread mulch around new plants, making the mulch 2 to 2 1/2 inches deep, says Ohio State University.
Keep the layer of mulch 2 to 3 inches away from the stems of woody plants to prevent disease and decay, advises Clemson Cooperative Extension. Keep mulch 6 to 12 inches away from building walls.
Spread black rubber mulch along pathways, slopes and areas that are prone to flooding, says Lowe's. The denser, heavier material will prevent mulch loss and will stay in place, even in heavier rains.
Calculate the quantity of mulch you need by measuring the length and width of the garden. Multiply the two figures together to get the area in square feet. Multiply the square footage by the mulch depth required in inches and divide by 324 to get the quantity of mulch you need in cubic feet.