One cubic yard of mulch (or nine 3-cu.ft. bags) will cover a 100-sq.ft. area to a depth of 3 inches.
Choose organic mulch if you want to both cover the soil and enrich it.
The faster the type of mulch percolates water, the longer it lasts. Pine nuggets are a great choice for flat areas because the particles tend to take a long time to decompose.
Mulch nuggets easily wash away on slopes. For hilly terrain, choose mulch that contains a mixture of many sizes.
Plan on applying shredded bark mulch about 3 inches deep. Spread very finely shredded hardwood no more than 2 to 3 inches deep; coarse nuggets, 3 to 5 inches; loose straw, up to 6 inches deep for wintertime protection of sensitive plants.
Avoid buying cypress mulch. The harvesting of cypress trees for this purpose has threatened valuable wetlands, primarily in the coastal areas of Louisiana. Cedar, pine bark and pine needles are excellent alternatives.
Rock mulches migrate. Use rocks or other inorganic mulch in areas where you don't plan to do any replanting and where foot traffic won't scatter the stones.
Dark bark mulches absorb heat from the sun and radiate it back up to plants. If you're choosing a dark bark mulch for a sunny area, select heat-tolerant plants. Don’t create “volcanoes” around trees. Leave a space of 8 inches between mulch and tree trunks.