Don't use grass clippings if you've treated the lawn with a weed killer. Leaves, previously composted, are more satisfactory. Noncomposted leaves, like fresh grass clippings, may compact and produce heat during decomposition. Sawdust and barkdust. Other wood sawdust and bark make an effective mulch.
Conifer needles make a light, airy, attractive mulch.
Bark chips are one of the most desirable organic mulching materials. They're long-lasting and not easily compacted. Don't stimulate excessive plant growth Fertilize lightly. Heavy fertilizer applications increase the salt concentration around the plant roots and make it more difficult for the plant to use whatever moisture might be in the soil. Overfertilization may also stimulate new, lush growth that increases the plants' demand for water.