A good starting point for pruning any plant is to remove dead, diseased, or damaged stems as soon as you see them. Dead stems attract insects and invite diseases to develop.
Also remove crossing branches, water sprouts (vigorous upright growing shoots that form on trunks or side branches), and suckers (vigorous shoots that develop near or from below ground).
Deadhead annual flowers regularly to keep them blooming well. Removing the old flowers prevents them from setting seed and allows plants to put more energy into blooming. Some annuals such as petunias sprawl and develop bare stems at their bases. As with perennials, you can shear these rangy plants to force more compact growth and renewed bloom.
Most perennial flowers look best if you remove faded flowers. This is called deadheading. As a bonus, many perennials will push out another cycle of blooms after deadheading.
If your perennial flowers become too tall and leggy, or flop open in the middle, try shearing them back to 6-12 inches above the ground. This type of haircut causes them to branch and become stockier.
True pines are more particular about their pruning needs than other needle-leaf evergreens. Pines form buds only at branch tips before the stem becomes woody.
For best results, prune pines only in the candle stage before the new shoots turn woody and before the needles have fully expanded. Prune only a portion of the new growth, removing up to half of the expanding candle.
Prune shade trees such as oak, linden, and ash when they are dormant in winter. It’s easiest to see the branching structure at this time of year, and you’re less likely to spread diseases through the pruning wounds. As with no blooming shrubs, avoid pruning them late in summer.
Roses that bloom only once per year the same as other spring-blooming shrubs: Pruning after they finish blooming. Repeat bloomers, including hybrid teas, floribundas, grandifloras, miniatures, and modern shrub roses are pruned mostly to shape the plant or to remove winter-damaged canes. If they become overgrown, cut them back in early spring.
Shrubs such as boxwood and privet are often sheared to form a hedge. To maintain a solid wall of green, shear the new growth frequently during the early part of the growing season. Keep the top narrower than the base so that the upper branches don’t shade the lower ones. Stop shearing the hedge approximately six weeks before your area’s average first frost.
Most hydrangea types — pink, blue, or white mop heads and lace caps, or oakleaf forms — bloom on old wood. Prune these types of hydrangeas before midsummer. If you prune them in winter or early spring, you’ll be removing flower buds. White-flowered types flower on new wood, so they can be pruned any time other than just before they bloom.
Flowering trees and shrubs
Early-spring bloomers, such as lilac, forsythia, and rhododendron, bear flowers on wood formed the previous year. The best time to prune them is late spring — immediately after they finish blooming. If you prune them later in the growing season or during winter, you’ll remove flower buds and decrease the amount of spring bloom.