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Proper pruning will help you keep your landscape plants healthy and within desired size limits. Pruning modifies growth for these purposes:
- to train and redirect growth
- to maintain health by removing dead or diseased wood
- to increase the quality or quantity of fruit or flowers
Don’t prune if one of these reasons is not your objective.
WHEN TO PRUNE
Pruning should be done in the proper season. There is little chance of damaging the plant if it is pruned during the dormant season. This is usually late winter and early spring, before new growth begins. Exceptions to this are ornamental plants that bloom in spring, which should be pruned after they finish blooming.
BASIC BUDS AND PLANT GROWTH
All plants develop terminal buds at the end of a stem or branch that cause the stem to grow in length. Lateral buds
grow along the sides of the stem, producing side shoots that cause a plant’s bushiness. Some plants also have latent buds that lie dormant beneath the bark. These buds will only grow when significant pruning or injury removes enough actively growing buds. The number of latent buds varies with each plant.
These basic points are important to remember when pruning. The terminal buds produce hormones that tell the plant
to send the majority of nutrients to the terminal bud, allowing the plant stem to grow longer. If you want the plant
to gain height, keep side growth pruned back. If you want the plant to become full and bushy, prune the tip where the terminal bud is growing. The lateral buds will all flourish and grow until one begins to dominate as the strongest and becomes the new terminal bud.
PRUNING SHRUBS
Heading Back applies the basic principles of the terminal bud and lateral buds to any tree or shrub. In heading back, you are cutting stems down to promising side branches or to lateral buds that will grow in the direction that you want. This is the primary technique used in pruning fruit trees.
Thinning keeps shrubs within the desired size limits. The best plan is to shorten a few of the longest branches back to the main trunk. This simplifies the plant’s structure and shortens the overall height of the plant, resulting in a shorter and bushier shrub. This technique is also useful when older, less vigorous growth needs to be removed, as in the case of roses.
Shearing is actually an indiscriminate form of heading back. It should only be used with densely foliaged plants that have buds and branches so close together on their stems that every cut is close to a growing point. Shape hedges wider at the bottom than the top. This will allow light to reach the bottom branches. If the top is wider and shades the bottom branches, then the base will become lanky and leafless.
PRUNING CUTS
It’s important to prune properly. The basic rule is to not leave stubs which allow for disease and insects to invade the plant. Always use sharp shears and saws. Ragged edges heal more slowly and provide lots of little spaces for diseases to enter the plant. When using scissors-action pruning shears, always cut with the blade, not the hook, on the side toward the plant
Correct pruning cut should always be made so that it slopes slightly back and away from the bud at which it is made.
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Heavy tree limbs should be cut in three stages. First, make a shallow cut on the underside of the branch. This will prevent the limb from tearing bark off the tree as it falls. Make the second cut from the top just over from the first cut to remove the limb. The final cut should remove the stub left behind. This cut should split the angle between the tree trunk and the bottom of the stub.
GENERAL GUIDELINES
There is an old saying that the best time to prune is when the knife is sharp. Making smooth, clean cuts will greatly reduce the time needed for cuts to heal over. A flush cut will heal over much faster than a stub. However, on larger branches that have formed a collar where the branch joins the trunk, cut flush with the collar, not the trunk. Branches should be supported while being cut so the bark does not tear. Slight pressure away from the cutting blade will make it easier to cut through branches. It is best to start at the center of the plant and make any necessary large cuts first, then work out to the ends and the smaller cuts.
The first to be removed is dead and diseased wood. It is a good idea to sterilize the pruning tools with rubbing alcohol immediately after pruning diseased wood to prevent spreading the disease. Then, remove water sprouts (branches that are growing vigorously upright). On fruit trees, remove dangling branches which produce small, poor fruit.
Next, remove branches that are crossing over or directly above or below another branch. Finally, thin out crowded branches. The hardest part about pruning is knowing when to stop. It may be necessary to leave even some dangling branches to avoid over pruning. Over pruning will cause many water sprouts to grow the following summer. Knowing when to stop has to be learned by experience.
PRUNING FLOWERING SHRUBS
Not every shrub in the garden needs pruning each year. Some require it and others need only rejuvenation after several years.
Pruning must be for a purpose; to promote better flowering or vigorous new stem growth and better foliage.
Pruning to contain size is the last reason. Better to initially choose the right size plant for the location intended and let it grow more closely to its natural size.
The method and timing of pruning deciduous flowering shrubs is governed by the age of the wood on which flowering takes place: this may be on the current season’s growth or on growth produced during the previous season.
SHRUBS WHICH FLOWER ON CURRENT SEASON’S GROWTH
Growth has to be made before flowering can take place, so shrubs within this group tend to flower in summer and autumn. If left unpruned, shrubs grow higher but with reduced vigour and more flowers are produced, but these are smaller and poorer in quality. Hard pruning means the removal of a large amount of wood so that the energy of the plant is diverted to fewer shoots and flowers which are consequently larger and better quality.
Prune in early spring when shrubs are dormant. Cut all shoots back and hard to within two or three buds of ground level or a framework.
Examples of shrubs in this group include Bluebeard, Butterfly Bush, Annabelle and PeeGee Hydrangeas, False Spirea and Pink or summer flowering Spireas.
The pruned shrub will have a low framework of main branches, from which shoots
will grow rapidly to produce flowers in summer.
SHRUBS WHICH FLOWER ON PREVIOUS SEASON’S GROWTH
Growth is made in one growing season and in the following year flowers are produced on this growth or on short laterals coming from it. This group tends to flower in spring. Pruning can be done directly after flowering in spring.
Shrubs in this group can be left unpruned but they tend to become too tall, less productive and tangled and unsightly. Prune out older and less productive wood as well as any that is dead or diseased. If the shrub is still crowded, thin out the weakest of the new-shoots and always cut just above a vigorous side branch.
PRUNING EVERGREENS
Evergreen shrubs such as Boxwood, Juniper, Cedar and Yew can be trimmed in spring. Clear the centre of leaves, debris and winter-damaged shoots. Upright types should be trained to a central leader and side shoots retained. Bush forms can be similarly trained or several leaders can be pruned. Further trimming may be required in formal plantings in summer once the new growth has emerged and hardened.
 Pines should be pruned when dormant to avoid excessive gumming. Select and train a single leader which should be
retrained if damaged by weather or insects. Dwarf forms such as Mugho Pine produce several leaders. Encourage bushiness by removing up to half of the candle-like new growth once it emerges in spring.
Hemlock, Spruce, and Fir can be pruned in mid-summer once new growth has emerged and hardened. Select and retain a central leader, keeping all side shoots as long as possible. Flowering evergreens such as a Rhododendron can be pruned immediately after flowering
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