Pruning Flowering Shrubs and Trees
To prune or not to prune?
Forsythia? azalea?
that is the question.
Pruning is a puzzle for many of us. There are two schools of thought about pruning forsythia. One group likes to cut off the tips of all the branches encouraging two or three branches to grow there. This makes a rounded bush. We like to use the thinning method. This means getting down on our knees and cutting some of the oldest branches at ground level. This produces a spray of branches. Forsythia should be pruned now if it needs it. The flower buds form on growth that comes this summer. If it is pruned before it flowers, it will have few if any flowers.
Other examples of bushes that should be pruned after they flower are lilac, bridal wreath, kerria, rhododendron and azalea. Lilacs bloom on second or third year shoots and continue to flower. If they are pruned, some of the oldest branches are removed. We rarely prune our lilacs, which are very old. Most of the blossoms are beyond our reach but they have made a lovely show this year.
It is important to think about why we are pruning. A light pruning helps control shape and size. We prune back to the base any branches which are crossing and rubbing on other branches, and sometimes cut away branches growing inward toward the trunk.
Many trees and shrubs resent being pruned when they are just leafing out. They need the carbohydrates that are stored in their roots at that time. It is better to prune them in the very early spring before the buds swell. Summer flowering shrubs that produce their flowers on “first-year wood” can be pruned then. First-year wood is a branch that both grows and produces flowers in the same year. Examples of these flowering shrubs are roses, hydrangea, rose-of-Sharon, butterfly bush, and potentilla.
Consider the role of fertilizer in the growth of a bush. Only fertilize bushes for specific reasons. If a plant is completely overgrown, it may be cut down to within six inches of the ground. Then fertilize to encourage new growth. If a property owner is spending all his or her time pruning back foliage, too much fertilizer may be the problem.
Getting back to timing, it is generally not a good idea to prune flowering shrubs in the fall. New shoots need time to harden off before winter sets in. Even with this precaution, the tips of some flowering shrubs may winter-kill, and those can be cut off in the spring to keep the plant looking neat.
We want to try some special tips given by Ruth S. Foster, a certified arborist writing in the April issue of Tree Care Industry magazine about pruning azaleas, rhododendrons and hydrangeas. Her recommendations are as follows: To increase flower buds on azaleas, watch for new shoots after flowering. Each growing tip produces three to five new shoots. When the new shoots, which are often covered with fuzz, reach about three sets of leaves, carefully nip out the growing tip with your fingers. Two or three new shoots will then sprout from the end and will set flowering buds in their season. On some species it is every year, on others it takes two years.
Rhododendrons flower only on the terminal end of a shoot, therefore pruning should be done only on the terminal end of a shoot. After flowering nip off the flower head. The next year two buds remain which grow into two shoots. Then those can be nipped to grow into two more shoots. Pruning should be done just above a whorl of leaves.
Hydrangeas are tricky to prune. When it comes to hydrangeas, the less the better. Generally on Macrophylla or French varieties, a single pruning to remove the oldest non-productive canes at ground level will do the trick. Sometimes it is necessary to renovate really scraggly hydrangeas, then try cutting the canes two feet from the ground and fertilize lightly.
The white paniculata varieties of hydrangea are often grown as small trees and have huge flowerheads at the end of each twig on gracefully drooping limbs. If you inherit one of these, don’t touch it. Just prune enough to keep it from breaking. When the ends are pruned in spring there will be more but smaller blooms.
This spring after our wonderfully scented mock orange bush has flowered, we plan to try drastic treatment. It is fifteen feet tall and about a third of the branches are dead. We plan to cut it all until only six inches are left above the ground and scratch fertilizer around it. We hope to see a mound of new leaves in a few weeks. It may be two or three years before it flowers again.
Perhaps our readers would like to tell us their experiences with pruning.
– Percy & Mary