Mulch should be applied no thicker then 4 inches with 2-3 inches being the optimum depth. Mulch should never be applied up against the trunks of trees or shrubs.
Mulch against a trunk can hold moisture against the trunk causing damage, provide insects with a cozy living and eating environment, and breed disease. Mulch that is too thick can hold too much moisture and block oxygen from the soil.
A finer mulch is preferred as it breaks down quicker providing nutrients to the soil.
Fall mulching should consist of removal of all old mulch and weeds in bed. Turning of the soil should be followed by a layer of newspaper covered by 1 to 2 inches of fine mulch. Fall mulch should decompose through out the winter and be ready to be turned into the soil with the newspaper in the Spring.
During the Spring check beds pulling weeds by hand and turning the existing mulch from fall. If the mulch appears diseased remove it. If you are to trim and prune hedges do so before adding new mulch.
Clean up the edge with and edger and shovels. If this is a new bed with little or no plants you can add landscaping fabric as a barrier against weeds. This landscape fabric should be removed in the Fall. Mulch is applied about 3 inches thick and leaving bare 4 to 6 inches around trees and shrubs.