Small trees and shrubs are an important part of most landscapes. While foliage can hide problems through the growing season, this is a good time of year to take a close look at branching patterns. It's also a good time to prune most woody plants. An easy rule of thumb is to "prune any time but leaf on or leaf off" -- in other words, when the plant's energy is focused on new growth or hardening off for winter.
Safety is an important issue for large trees, and pruning a good-sized tree can be expensive and require specialized skills and equipment. Fortunately, though, even large-maturing trees that are carefully pruned when small will be stronger and require very little pruning once mature.
Small and young trees are pruned primarily for plant health and for aesthetics. But even the smallest woody plant can quickly turn into a mass of tangled branches.
Where to begin?
- Start by removing branches that are dead or injured from disease, insects, winds, etc. The pruning cut should be angled from the base of the trunk about an inch or so out (a slightly elevated ridge of bark may be visible).
- Eliminate branches that are rubbing against other branches.
- Remove branches with weak or narrow angles of attachment, which are likely to crack or break off. Branches that are angled 60-70 degrees out from the trunk are much stronger.
- Prune to encourage and not interfere with flowering, usually immediately after flowering: lilac, magnolia, chokeberry, chokecherry, serviceberry, clove currant, forsythia, early-blooming spirea, viburnum, etc.
- Shrubs grown for foliage -- burning bush, dogwood, honeysuckle, ninebark, sumac -- should be pruned before leafing occurs.
- Prune to increase air flow, or to allow sunlight for plants underneath the tree.
- Remove sprouts and suckers in early summer to minimize re-growth.
With newly planted trees, avoid excessive pruning while the plant is developing its root system. Cut back only dead or injured branches to limit plant stress. The main trunk will develop more quickly if lower branches are left on for several years. A few months after transplanting, prune to maintain a central leader and to space branches out around the trunk and vertically.
Deciduous shrubs can be improved in a number of ways: thinning them out from near the base will result in a more open plant and won't stimulate excessive growth. For gradual renewal or rejuvenation, remove older, longer branches near ground level over a period of several years.
With narrow-leaved evergreens like arborvitae, pfitzer junipers and yews, remove dead branches as they occur. To encourage compact growth, the tip ends of new growth can be trimmed each year.
Pines and most other evergreens require very little pruning, although it may be necessary to remove multiple leaders to encourage the growth of a central leader.
Well-shaped deciduous hedges require some effort. To induce low-branching, it's best to select small shrubs with multiple stems and cut them back to 6-8 inches at the time of planting. Prune off half the new growth the following season, and again the following year. It's best to trim when new growth is less than 1 foot long. Evergreen hedges can be shaped as they grow, but not as severely as deciduous since new growth is less likely to occur. Keep the top of the hedge narrower than lower branches. Rounded shapes require less trimming than straight sides and the more natural the pruning, the more likely it is to maintain its shape.
To avoid disease and insect problems, avoid pruning elms from April to October; oaks from April to June when they may be susceptible to oak wilt; and birches in June, when weeping from the cuts may attract insects or diseases.