Encourage a plant’s natural habit with the right cuts. Shape it using heading cuts: Hold pruners at a slight angle about inch above a bud that faces the direction in which you want to encourage the new growth. To reduce overall size, use thinning cuts—removing a branch at its origin—in moderation.
Arborvitae, juniper, and other trees and shrubs with fan-like needles should be cut back by no more than about 20 percent, says TOH landscape designer Jenn Nawada. Prune off more and you might inadvertently create a dead zone: At least some green needles need to remain or new growth will not develop.
Short, Flat Needles
Hemlock, yew, and other evergreens with short, flat needles should be pruned before new growth appears in order to maintain their size. These and other random-branching trees and shrubs will produce new shoots both at branch tips and farther back on branches that still have needles.
Short, Sharp Needles
Spruce, fir, and whorl-branched trees and shrubs that have short, sharp needles can be trimmed all the way back to a lateral branch or dormant bud; dead bottom branches should be removed. Though you can hold off a little longer with these trees, it’s best to cut in cold weather so that they “bleed” less sap.
...but hold off on long-needled pines. These trees and shrubs shouldn’t be pruned until they are in active growth mode, which is not until June in the coldest zones. Then, use your fingers to pinch back one-third or one-half of the new candles. New growth won’t develop if you cut into the woody stems.