How to keep your trees in shape (© Cultura Creative/Alamy)

© Cultura Creative/Alamy

Remember that sapling you planted in the front yard when Junior was born? Well, Junior turned 7 last week, and he's not the only one growing up fast: That birthday tree could use some tending, too — along with the other trees in your yard.

But you know as much about tree pruning as you do about differential calculus, right? Fear not. The basics are not mystical. (Bing: How to train a young tree?)

Here's expert advice on caring for your trees — and how to tell if one is about to fall.

What to look for
"We put trees into places where nature hasn't put them, so we have to manage them," says Curtis Smith, an extension horticulture specialist emeritus at New Mexico State University. "Pruning is necessary to keep the tree safe for our sake and for its own sake."

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When does your tree need care? Smith, who has written a good overview on pruning (PDF), recommends looking for these warning signs:

  • Dead, dying or diseased branches.
  • Branches that cross one another. "(This) rubs the bark off and opens the tree up for disease entry," he says.
  • Sprouts forming at the base of the tree's trunk. These can be a sign that the tree is injured and is redirecting its energy.
  • V-shaped crotches between branches and the trunk: A tight-angled V can indicate a weak point in the tree, if the bark grows inward instead of outward, he says.
  • Multiple leaders, or near-vertical branches that compete to be the main trunk of the tree. They can get quite large and cause damage if one splits off. 
  • Nuisance growth, or when a tree interferes with power lines, sidewalks or traffic.

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When to prune
When is the right time to prune?

"The adage is that the best time to prune is when your saw is sharp," says Nolan Rundquist, arborist for Seattle's Department of Transportation.

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There's truth to that old, ahem, saw. Pruning can be done at different times of year, depending on location and trees, experts say. But the pros do offer some guidelines:

  • Cut when it won't hurt. "Most pruning — significant pruning, when you take away living tissue — is best done during the dormant season, from the time the leaves fall until the time the buds begin to swell again," Smith says.

For deciduous trees, that means once leaves have fallen in October or November. But January to March may be better for other trees, Smith says. Conifers are better pruned in late winter, for example.

"Much of a tree's carbohydrates and nutrients are stored in the roots and wood," Smith says, "so few of the food resources needed for growth and overall health will be lost when a limb is removed." Trees trimmed too early in the winter can dry out in the dry, cold wind and winter sun.

  • Summer can be for reshaping. "The best time to cut dead wood from a tree is in the summer, because that's when you can tell it's dead wood," Smith says. Rundquist also says mid- to late-summer thinning can be beneficial because trees are in full leaf, and a homeowner can see the tree's full shape.

Also, "Summer pruning is often recommended for spring-flowering trees" or shrubs such as crabapples, flowering pears, lilacs and forsythia, "which carry pre-formed flower buds through the winter," Smith says.

  • Take the spring off. Give your pruners a rest during the period of most active growth. Finish any pruning "before the buds show color," Smith says. "Then it's time to stop." Why? Smith likens a tree to a bank: In the spring, the tree has invested a huge amount of time and energy in new buds. If you cut them, "You've stolen that investment from the tree."

  •  When in doubt, check what's best. While many trees can be trimmed at various times of year, some trees shouldn't be trimmed at certain times, says Joe Hendrickson, an arborist and owner of Hendrickson Tree Care in Overland Park, Kan. "For example, in the Kansas City area, we have a disease called oak wilt that affects oak trees," says Hendrickson, adding that those trees should be pruned when spores are dispersed in the spring. When in doubt, consult an arborist.

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How to make the kindest cut
So you've dusted off the loppers. Now what? Don't just attack that tree as if it were a bonsai. Here are some rules of thumb about technique:

  • Think before you cut. "If you do not know the reason, then do not make the cut," Hendrickson says. After all, you can always cut later, but you can't undo a mistake. For more information, take a class at your local cooperative-extension service, or check out pruning tip sheets for young and mature trees here.
  • Think about spacing and direction. Always try to cut back to a twig, branch or bud that's pointed in the direction you want the new tree to grow. It's "training" the tree, Smith says. "You've directed the growth." When deciding which branches to keep and which to trim, choose branches that have an angle of more than 30 degrees from where they meet the trunk; they usually grow stronger and can support snow and wind.
  • Make three cuts. Cutting larger limbs isn't as simple as chop chop. They should be removed using three smaller cuts, experts say. This prevents "having the bark rip down the bark of the tree and damage below the point of the cut," Smith says. The first cut should be about one-third of the way through the branch on the underside of the limb, several inches out from the trunk. The second cut, from the top down, should occur several more inches out from the trunk and be made until the branch falls away. Once the branch is gone, a third cut clears the stub. See illustrations here.
  • Leave a collar. Where a branch meets the trunk, the tree forms a "collar" — a ring or bump full of vascular tissue. If you injure that collar, "You will interfere with the tree's natural protective mechanisms, allowing the entry of disease and insect pests that damage the tree trunk," Smith says. So when you trim a limb, don't remove it flush to the trunk; leave that protective bump, Smith says.