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Prune now for healthy trees in the summertime

Late winter or very early spring is the right time to prune most woody plants, including fruit trees and most deciduous trees and shrubs. Yet common practice would lead us to think otherwise.

So many people cut back their landscape plants in fall, either to get ready for winter, or because they then decide a woody plant is too tall. People tend to do what's convenient for people, not what's good for trees.

Bad pruning is a major cause of tree failure. Even folks who have no love or reverence for trees should see that it's expensive or even dangerous to weaken a tree and set it up for early decline and death. And it's simply foolish to damage an ornamental shrub that's been purchased.

So why doesn't everybody learn the art and science of pruning?

When I contemplated writing about (and soon teaching) pruning this week, I was frankly out of zip. When a novelist reaches that point, she might turn to F. Scott Fitzgerald or Joyce Carol Oates for refreshment, or the work of great writing teachers for inspiration. When a garden writer needs a kick in the pants to cover pruning, she goes back to Alex Shigo.

Considered "the father of modern arboriculture," Shigo, Ph.D, turned the arboriculture world on its ear with his discoveries about how trees grow and respond to wounds.

Decades of work with the U.S. Forest Service, during which he is said to have "dissected 15,000 trees with a chain saw," led him to teach and write more than 200 publications to teach responsible tree care.

>The bad things we do

"Improper Pruning:

Destroys Tree Beauty,

Destroys Tree Defense Systems,

Destroys Tree Dignity."

-- From "Tree Pruning: A Worldwide Photo Guide," by Alex L. Shigo (Shigo & Trees Associates, 1989)

These are the basic mistakes we can see all around us, especially as we look at town and city trees, according to Shigo and the tree science that has been built on his shoulders:

*Wrong tree, wrong place: The fate of a tree starts on the day you choose it. No matter how healthy the specimen, it is dependent upon the soil and site it's stuck with. Trees grow, and even the smallest species usually surpass 25 feet tall. When a tree outgrows its desired space, it is typically mutilated. Choose plants that will tolerate and won't outgrow the site you have.

*Flush cuts: Until the work of Shigo and his followers became available, most people were taught to cut branches off trees flush with the trunk, straight down. Those cuts took off the "branch collars," the rings of wood with living cells that form a tree's defense system. The open wounds that remained left trees vulnerable to disease and unable to seal.

(Compartmentalization -- the ability to close off a cut or diseased area -- was a major Shigo discovery, and one of the ways that a tree's "sealing off wounds" is different from human healing.)

A proper cut is just outside the branch collar. Where a tree branch has been cut off correctly, you will see a fat circle or collar around the cut, that looks something like a doughnut.

*Stub cuts: Whenever you see a branch stub sticking out from a tree, it's a bad cut. A stub is asking for fungal rot diseases or cankers; there are no disease-fighting cells where the cut was made. Cut outside the branch collar or just above where another branch emerges.

*Topping trees: Tree lovers call it "a crime against nature." Topping trees to attempt to shorten them leads to disease, decline and deformity.

Trees respond to topping with lots of growth, that many people interpret as the tree's vibrant health, but actually the regrowth is weak growth that is easily damaged. When you cut off a tree's leader, you have removed a kind of hormonal mission-control system. (The leader's growth inhibits and directs the growth of subordinate branches; when the leader is gone, the growth goes wild.)

Of course, the need to top a tree -- often by utility companies that must protect wires and property -- started when the tree was planted in the wrong location. Look up before you plant. Read about the tree's potential height before it goes under a wire or another obstacle. Trees take a long time to die, but topping starts the process. It never works out well.

*Over pruning: Cuts are wounds. Even good pruning makes wounds, that increase the odds of disease or insect infestation, or that remove some of the future leaves that will photosynthesize and help the tree grow.

Overdoing it, cutting out too many branches in one season, weakens a tree, increases sprouting, encourages borers and threatens root health. For young trees, unless there is a need for serious correction, many arborists suggest holding off pruning for at least five years.

Another rule of thumb is never to remove more than a quarter (in some cases a third) of a tree's branches.

*Dressing wounds: Wound dressings generally don't prevent rot, and the dressings may actually increase some rotting or cause another problem. Homeowners shouldn't automatically paint on wound dressings. However, arborists strongly recommend some dressings to prevent specific problems; consult a professional arborist.

>Why prune now?

While plants are dormant, the carbohydrates and nutrients are still stored in the roots and wood; you aren't stealing energy from the tree. Once the tree has leaves, many of the food reserves are in the leaves. Dormant season pruning also lessens "bleeding" for most genera.

These are examples of the tree and shrub groups you may prune now.

*Fruit trees and most deciduous trees

*Narrow-leaved evergreens (arborvitae, juniper, yew)

*Broad-leaved evergreens, except spring-flowering ones: (boxwood, euonymus, privet)

*Summer-flowering deciduous shrubs or vines (buddleia, late flowering hydrangeas, rose of Sharon, trumpet vine)

*Red-twigged dogwoods or other plants with colorful new growth; cut to the ground if you wish for the brightest branches.

*Shrub roses, Rosa rugosa

Don't prune spring-flowering shrubs yet. Don't cut back the sticks of 'Endless Summer' hydrangeas and kin. Leave roses alone for a while. On any plant you can always prune out a dead or dangerous branch, a branch that rubs on another or a crowded inner branch any time.

Bad pruning damages plant health; good pruning improves it. Before you march out there, shears and knives in hand, do get to a pruning class or study a pruning book. The plants will be grateful.

Sally Cunningham is a garden writer, lecturer and consultant.