Ask a hundred gardeners “When is the best time to prune?” and you may get a hundred answers. Some highly respected nurserymen and academics maintain that the best time is whenever your plants need the attention and you have the time to do the job. Often, however, the answer depends on a plant’s condition, the length of the growing season, and your pruning goals — do you want maximum flowering or damage repair? Give your plants a touch-up or take off a dead, sick, or broken limb as needed, but wait until dormancy for more extensive pruning.
Q When’s the best time to prune my trees and shrubs?
A Because of the tremendous difference in weather conditions throughout the continent, it is difficult to give precise directions on exactly when to prune. See individual chapters for more specific advice for different types of trees and shrubs.
SEE ALSO: Plant-by-Plant Pruning Guide, starting on page 311.
Q Why should I prune in winter to early spring?
A Most gardeners like to do major pruning on their trees and shrubs when they’re dormant, in late winter or early spring. The time is just before the surge of new spring growth, when deciduous branches are bare, so it’s easy to see what you’re doing. Since “late winter” and “early spring” mean a different time in each locale, take it to mean whenever the days begin to lengthen but before the ground warms up, the buds swell, and new growth begins.
Although late-winter pruning encourages fast regrowth of wood, avoid taking off too many leafy branches in one season. Some experts say you can remove up to 25 percent of the crown in a year without harming a tree (depending on the species). However, 10 to 15 percent is better, because too much pruning weakens trees, particularly old ones. Removing too many branches may cause profuse suckers and water sprouts to grow, signs of a tree under stress or in decline.
Make cuts just to the outside of the branch collar to allow the tree to seal over as well as possible. Large pruning cuts take a lot of energy for the tree to deal with, so make sure you avoid making too many large cuts on one plant in the same season.
SAPPY TREES
Some trees appear to “bleed” a lot of sap if pruned in early spring. Don’t worry if you see sap running from the cuts on maples, birches, willows, walnuts, beeches, hornbeams, and yellowwoods pruned at this time. They’re not bleeding, and sap flow won’t hurt them. If you prefer to wait until less sap is flowing, prune in midsummer. Before pruning in summer, though, check first with your local Cooperative Extension Service to ensure that summer pruning is not harmful to your particular species. For example, don’t prune white-barked birches — which are more susceptible to bronze birch borers than other birches are — between May and September, when these insects are flying.
Q What are the best plants to prune in late winter to early spring?
A You can prune flowering trees, fruit trees, woody vines, conifers, and broadleaf evergreens. However, late-winter pruning reduces the number of blossoms on spring-flowering trees and shrubs, so delay pruning these until right after flowering if maximum bloom is your goal. Most roses do well when pruned in very early spring, around the time the forsythia blooms.
Q Why prune trees and shrubs when dormant?
A Plant dormancy is a type of hibernation that occurs in late fall and lasts into early spring, before growth starts. In late fall, deciduous plants have dropped their leaves and stopped growing aboveground. Underground plant growth slows but continues until halted by deep ground frost. In dormancy, you can see the form of deciduous plants and correct disease, insect, and shearing damage. Also, you can take advantage of a plant’s spring growth spurt to cover pruning cuts and hasten the plant’s recovery. Dormancy is also a good time to thin broadleaved evergreens and let more light into the canopy of deciduous trees.
Q Can I prune trees after they leaf out in spring?
A Enjoy your trees in spring, but don’t prune them when actively growing in mid-spring. Aside from removing dead or damaged wood, pruning trees during their major growth spurt brings such unwanted results as increased suckers.
Pruning trees after the spring growth flush reduces their growth rate, which is useful to control plant size. It’s also a good time to prune hedges, since new growth will be slowed. Why the slowdown? You’re decreasing the tree’s leafy space, and thus lowering the food production needed for robust growth.
Q Which trees and shrubs do I prune in late spring and summer?
A Prune spring-flowering plants that bloom on old wood, such as dogwood, lilac, bridal wreath, and spring-blossoming spirea, immediately after blooming. You can enjoy their flowering, and they can develop a new set of buds for the next spring. Prune oakleaf and bigleaf hydrangeas when the flowers fade. If you see broken branches needing removal, it’s okay to take them off. You can also shear evergreen hedges and prune conifers right after spring growth occurs.
Q Late summer and fall are great times to work outdoors. What can I prune at this time?
A Avoid pruning woody plants in late summer and early fall, since plants are particularly susceptible to fungal diseases at this time. Also, new growth may not have time to harden before cold weather arrives. This practice can result in winter injury that needs correcting with additional pruning in spring. By November, woody plants will probably be dormant and you can do corrective pruning by removing dead, diseased, and damaged material.