Leaves are another garden secret. Composted, they are a source of "brown" materials; shredded, they can be used as mulch (leaves and chipped brush and twigs can be used as mulch around the bottoms of trees and plants. Mulch holds moisture so you won't have to water plants as often. It also controls weeds and keeps plants from freezing when temperatures drop). In wooded areas, where they should be left on the ground, they provide nutrients and retain moisture.