One cubic yard of mulch equals 27 cubic feet. A cubic yard will cover about 100 square feet 3 inches deep. Multiply the length and width of an area to get the square footage. Depending on the type of mulch you use, a layer of 2 to 5 inches makes a good, effective covering. Try not to use more than that.
Deep mulch can suffocate plants' roots by stopping free air exchange.
It blocks the penetration of water and fertilizers into the soil. You can apply mulch any time during the year, but it's best to mulch your vegetable or flower garden in the spring after the soil has warmed up. Cool, wet soils slow seed germination and increase the decay of seeds and seedlings. If you're using mulch to insulate your plants during the winter, apply it late in the fall after the ground arrive. This mulch should be made of loose materials, such as straw, hay or pine boughs, that will not compact under the weight of snow and ice.