Prune Dead, Damaged, and Dying Branches
Anyone apprehensive about taking a saw to a live shrub or tree can start small and simply. Rule of thumb: Prune according to the 3Ds -- dead, damaged, or dying branches. For the tree or shrub's health, it's okay to remove the 3Ds anytime. These branches are easy to spot: dead or dying branches snap off easily and are brown or black inside; damaged branches may be broken or visibly damaged by insects.
Prune Dormant Woodies
The standard advice has been to prune when trees and shrubs are dormant. According to Iowa State University's Horticulture Department Web site, the best time to prune deciduous trees, including fruit trees, is late winter or early spring before the trees leaf out. Start routine pruning to direct growth when the tree is young; annual maintenance pruning will be easier on both you and the tree you're training.
Prune Summer-Flowering Shrubs
Summer-flowering shrubs, such as potentilla and spirea, bloom on the current season's growth. So pruning them in late winter or early spring won't diminish flowering. Wait till spring to prune lavender, rosemary, and butterfly bush, though; hold the pruning till you see green leaves that show the shrub's beginning to regrow.
Take Care When Pruning Spring-Flowering Shrubs
Pruning spring-flowering shrubs, such as azaleas, lilacs, and forsythia, in winter will remove branches that have flower buds. Best to do light pruning on them immediately after they bloom. If they're overgrown and need rejuvenation though, late winter or early spring pruning is best. They may not flower profusely for a year or two, but they'll grow healthier and produce more flowers over time.
If you haven't already done so, mulch your trees, shrubs, perennials. Put 3 inches of organic mulch -- crushed leaves, root or bark mulch, pine straw -- like a blanket over the root area. Leave 2 to 3 inches of open space between the plant's branches, stems, or trunk and the mulch. MULCH plus MOISTURE touching a plant part equals ROT. Organic mulch will provide an insulating layer to help reduce frost heaving that can break up the crown and kill the plant. Mulch will also help to moderate temperature extremes, conserve soil moisture, and reduce weed competition.