I need some advice about pruning a PeeGee hydrangea tree, an apple tree and lilacs. When should I prune them and how much should I take off?
Late February through March is the ideal time to prune many trees and shrubs, including your hydrangea and your apple tree, but not necessarily spring-bloomers such as your lilacs. Read on for a quick primer on pruning.
Why prune now?
The goal is to have the pruning wounds exposed to the elements for as short a time as possible. In late winter the plants are still dormant, but soon they'll begin growing again. In spring, plants use their stored energy for the rapid cell division needed for leaf expansion. Rapid cell division also allows plants to quickly cover pruning wounds with a protective layer called callus tissue. The quicker a cut is covered, the less chance of underlying tissues drying out or being invaded by pathogens.
Most summer-blooming shrubs, such as panicle hydrangeas, can be pruned now. PeeGee hydrangea (Hydrangea paniculata 'Grandiflora') is a cultivar of panicle hydrangea noted for its late summer display of huge, showy flower clusters. PeeGee hydrangeas are available in two forms: multi-stemmed shrubs or single-stemmed small trees.
Since you have the tree form, your pruning goals are fairly simple. First, you want to maintain the hydrangea as a single-stemmed plant. PeeGee hydrangeas generally don't send up many suckers (new stems arising around the base of the plant), but if there are any, prune them off at the ground. Also prune any side branches that have developed on the lower trunk.
Now all you need to do is to thin some of the branches that form the fountainlike top of the hydrangea. The goal here is to retain a natural shape while still thinning the branch density
First, remove any broken or damaged branches. Then, selectively remove some branches entirely by cutting them off where they attach to the main trunk. You can also control straggly branches by cutting back to a healthy side branch.
One note of caution: Never remove more than one-quarter to one-third of the branches at one time on any plant.
Pruning apple trees
Since most apple trees are grown for fruit, they aren't pruned the same way shade trees are pruned. To get the largest quantity and highest quality fruit, apple trees should be pruned to allow plenty of air circulation and sunlight penetration. This kind of pruning makes fruit trees more open and spare looking, not something most people want in a shade tree.
Ideally, an apple tree should have one central trunk with a series of well-spaced scaffold limbs going up the trunk. Apples are produced on short, spur-like branches attached to the main branches, so avoid pruning off short spurs.
For more detailed information on pruning apple trees consult the book "Growing Fruit in the Upper Midwest," by Don Gordon (University of Minnesota Press, $24.95) or visit some websites such as cecommerce.uwex.edu and search on apple pruning.
What about lilacs?
For spring-blooming shrubs such as lilacs, forsythia, azaleas and early spireas there are two possible pruning strategies: prune in late winter, or prune immediately after bloom in the spring.
These shrubs bloom on old wood (growth from the previous year), so if you remove branches in late winter you will be removing flower buds that would have bloomed in the spring. If you just want to thin out some stems and cut back a few branches, you probably won't notice the loss of flowers because there still will be plenty left on the remaining stems.
However, if you are pruning to reduce the height of the entire plant, you will eliminate much of the spring blooms if you prune in late winter. In this case, it would be best to wait until just after the shrub finishes flowering to prune.