For best results, planting beds, tree rings, and shrub beds should be cleared of any existing weeds before the mulch is applied and spread. You may also want to install a weed barrier (available at most garden supply centers) to help prevent new growth of weeds or grass. This is not always necessary, although most people prefer to do so as a precautionary step in weed control.
Care should be taken in not piling up the mulch too closely to the trunks of trees and shrubs, as well as the stems of plants in your garden beds. One problem with piling the mulch too closely is that during the colder winter months, mice, moles, and other small rodents tend to burrow in this warm area and eat away at the bark. This can lead to stem damage or even kill your trees and shrubs.