May 16, 2008
Garden Detective: Prune your woody plants now
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Mid-February to mid-April is the ideal time for pruning most woody plants, both because they're dormant and because you can better see what you're doing when your view isn't obstructed by leaves. It's also the period of most rapid plant healing, called compartmentalization.
If you're unable to prune now, wait until July, which is the next-best time to prune. (For the record, late spring is the absolute worst time to prune. Removing new spring growth at a time when the plant is vulnerable means it won't be able to compensate adequately. Also, photosynthesis is beginning, and the plant is at its weakest.)
I was fortunate to learn about pruning, defined as the selective removal of plant parts for a purpose, from Richard Weir III. For the unindoctrinated, Weir was the program manager for horticultural and environmental issues for the Cornell Cooperative Extension of Nassau County. He's also a pruning expert and co-author of "Pruning: An Illustrated Guide to Pruning Ornamental Trees and Shrubs." (The entire manual is available online in PDF format at www.gardening.cornell.edu /woodies/.)
There are many reasons you might consider pruning. The most common is to maintain plant health and appearance. Other reasons include training young plants to enhance their form, controlling size, preventing injury to people and property, opening a vista, rejuvenating old shrubs and developing unnatural forms (think bonsai and those Dr. Seuss-like evergreen topiaries that are popular these days).
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First, you'll need to get the right tools: Invest in a good bypass-type pruner (avoid the anvil type), a folding saw and gloves.
There are two types of pruning - selective and rejuvenative. Selective means what it sounds like: You select certain branches to remove and you have a reason for doing so. Rejuvenative is a severe cutting-back performed with the intention of rejuvenating an older plant.
Broadleaf evergreen shrubs should undergo only selective pruning, and they can take it at any time of year.
Narrow-leaf evergreens should undergo selective maintenance pruning only. Always remove more from the top than from the bottom. This will allow sunlight to reach the bottom of the plant. Overshearing or creating a hole in the form of narrow-leaf evergreens will be problematic. They never will fill in. The only exception to this is the yew (Taxus). Yews are also the only narrow-leafed evergreens that can take severe pruning.
Rejuvenation pruning is the extreme cutting back of overgrown, unproductive shrubs. There are three basic methods for doing this: severing the whole plant at the crown, where the stem meets the roots; pruning all the branches at unequal heights all at once, and a multiyear sequential pruning. Plants must be healthy and vigorous to undergo any type of rejuvenation pruning. The latter method is the least severe but requires the most patience. The first method is actually the best. Plants should be fertilized well after undergoing any rejuvenative pruning.
When it comes to hedges, there's only one basic rule: The bottom must remain wider than the top. If the plant thins out at the bottom, the only way to correct it is to cut the entire hedge down to 6 to 8 inches from the ground and wait for it to grow back. You don't want to go there.
When pruning shrubs and trees with thin branches, use the pruner to remove crisscrossed limbs, dead wood and branches that are growing into the tree's canopy. But when removing a branch with a diameter of more than 1 inch, never make a flush cut, which would remove the branch collar and create a bigger wound.
Instead, use your saw for the three-cut method:
Cut the branch halfway through from underneath, a few inches from the trunk.
Move your saw a few inches father away from the trunk and cut the branch off from the top. This eliminates the weight of the branch and prevents tearing. Make the third and final cut just outside the branch-bark ridge, sawing through the entire branch to the outside of the collar. If you were to make this complete cut without having done steps 1 and 2, the weight of the branch would cause it to rip just before separating and the tree would have a difficult recovery and a larger area through which disease could enter.
It's not necessary to treat the wound with tree paint or tar. In fact, it can do more harm than good. Avoid it.
PRUNING CALENDAR
Notes and exceptions:
For spring bloomers like lilacs, it's best to wait until after their flowers fall. It's fine to prune now, but you'll be removing flower buds and have fewer blossoms this year. It's up to you.
Forsythia and privet should be pruned every year. Spirea and weigela should be pruned every two to three years.
Clethra and cotoneasters should seldom be pruned.
Butterfly bush (Buddleia) should never be pruned in fall or it will die. Instead, cut it all the way to the ground every year in early spring.
Only deadhead rhododendrons and mountain laurels if they aren't full enough, and do it immediately after flowering. Waiting even a week will defeat the process and you'll still end up with leggy plants.
Hydrangeas are in a category all their own. Actually, they're in several categories. Here are the basics:
Hydrangea macrophylla: Prune in late summer, as soon as the flowers fade, but never after September. Remove weaker stems from the base of the plant, being careful to retain several stems of old wood, which will produce buds for next year's flowers. You can prune now, too, but it will cost you flowers this year.
Hydrangea arborescens 'Grandiflora': Cut to the ground in late winter/early spring. If it survived the winter nicely, however, and you'd like it to grow better, do a light selective pruning, cutting branches at varying heights.
Hydrangea paniculata 'Grandiflora' (Peegee): Simply remove spent flowers and thin or cut back last year's growth in late winter/early spring.
Hydrangea quercifolia (oakleaf hydrangea): Remove dead wood at the base of the plant in early spring.
Hydrangea anomala petiolaris (climbing hydrangea): Unruly vines can be shortened in summer. Otherwise, pruning is seldom necessary.
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