As fall clean-up continues, some handy reference charts have helped with decisions re: whether to prune now or in the spring and about the optimal time to move plants to new locations in the garden.
Broad-leaved evergreens (Rhododendrons,...): Broad-leaved evergreens require little pruning. Most grow very slowly. If pruning does become necessary, selectively prune branches back to a side branch so that the foliage hides the pruning cuts. Broad-leaved evergreens should not be sheared or cut back into older, non-leafy areas as these plants lack latent buds. New growth is initiated from terminal buds.
Spring-flowering shrubs (lilacs, forsythia, viburnums, honeysuckle, chokeberry, mock orange, weigela): Spring-flowering shrubs produce flower buds on one-year-old wood produced the preceding summer. Prune these shrubs AFTER they have flowered in spring, but before the next year's flower buds are set. If you prune these shrubs in winter or early spring, you will remove many of the flower buds. Spring-flowering shrubs that sucker readily from the base benefit from thinning
Summer-flowering shrubs (hydrangeas, roses, rose-of-Sharon, smokebush): Summer-flowering shrubs produce flower buds on new growth in the spring. Prune these shrubs when they are dormant or in early spring before budbreak. If you postpone pruning until late spring or early summer, you will remove many flower buds. Examples of summer-flowering shrubs are hydrangeas, roses, Japanese spirea, rose-of-Sharon, potentilla, and smokebush.
Evergreen trees such as pine, spruce, fir, Douglas-fir, and hemlock require little pruning. These trees typically have a broad, pyramidal form with low branches, and should be left intact. DO NOT remove lower branches as this destroys the natural aesthetic form of the tree. NEVER remove the main, central stem. DO remove crossing, dead, diseased, or broken branches. Also remove individual branches to help maintain the tree’s natural outline. When pruning large branches, use the 3-point method of pruning.
Pines: New growth in pines occurs once a year from terminal buds. To maintain a more compact, densely branched habit, remove approximately 1∕2 to 2∕3 of the elongated terminal buds (candles) before the needles expand in spring. Candles can be pinched in half (see figure), or pruned with hand pruners. Do not cut branches back to older growth farther down the stem. Pines produce buds only at the tips of the current season's growth and will not produce new shoots farther back down the stem.
Spruce, fir, and Douglas-fir: New growth in these trees occurs once a year from terminal buds. To maintain the tree’s natural shape and promote denser growth, cut the tip of the branch back to a lateral bud. Do not leave branch stubs. In early summer, you can also remove 2∕3 of an unbranched tip to keep the tree fuller.
Hemlocks, arborvitae, and yews: These evergreen trees and shrubs have latent (dormant) buds farther back down the stem. You can also prune them in spring before the new growth has expanded because any subsequent growth will hide the pruning cuts. You can also shear these evergreens in late spring or early summer after new growth has expanded. You can also prune individual branches back to a bud or a branch to encourage more compact habit. If these evergreens are used in formal hedges, maintain the base of the hedge wider than the top to insure adequate light penetration to the bottom of the hedge.
Junipers and false cypress: These shrubs require little pruning. They have scale and awl-like foliage that can be tip pruned in summer. Selectively prune branches of these plants back to a side branch, so that pruning cuts are hidden under foliage. These plants should NOT be sheared or cut back to older, non-leafy areas because this type of pruning would take years for new growth to conceal. Do not prune these plants after August, as the new growth will not harden off sufficiently before winter.
Types of pruning
Thinning: This technique is the most common and best way to renew a shrub, preserving the overall plant shape. It is particularly useful for shrubs that sucker from its base Remove interior branches with loppers or a pruning saw back to the base of the plant or the point of origin. Remove only 1∕3 of the largest branches at one time.
Heading back: Heading back can be used to reduce the height of most types of shrubs. This technique entails removing each branch back to a larger branch or bud. When pruning back to a bud, cut the branch on a slight angle to within ¼ inch above the bud. DO NOT leave a stub. Disinfect your pruning tools with alcohol or a 10% bleach solution after each cut to avoid spreading diseases. Wound treatments are not recommended and can actually slow down wound closure.
Rejuvenation: Use this technique for shrubs that are overgrown or leggy, and for shrubs that sucker readily from the base. Cut the entire shrub back to a height of four to 10 inches from the ground when the shrubs are dormant. Shrubs that can tolerate rejuvenation pruning include butterfly bush, and Annabelle hydrangea.
Shearing: This technique involves the removal of new shoots using hedge shears. Shearing should be used only on formal hedges. Examples of shrubs that can be sheared into formal hedges are yews, and arborvitae. Maintain the base of formal hedges wider than the top to insure adequate light penetration to the bottom of the hedge. Each time you shear a hedge, leave one inch of previous growth to allow for the plant to regrow. Most shrubs should NOT be pruned with hedge shears since they will eliminate the shrub’s natural form, reducing the amount of foliage and flowers in the shrub’s interior, and causing a proliferation of shoots that will make the shrub unsightly.
Pinching: This technique involves the removal of shoot tips allowing for additional side branching. Pinching increases the bushiness of a shrub. This type of pruning can be done on smaller shrubs in spring, or on certain evergreens.
Deadheading: This technique involves the removal of spent flowers by hand. For some shrubs such as roses, deadheading can encourage another flush of flowers.