rinda's blog
Spring is the traditional time for pruning. (In my house, we never talk about spring cleaning. Just spring pruning.) But you have to know what to prune when or you end up with a flower-free season.

There are three reasons for pruning: I'll take these in order.

When you want to keep a plant - say a shrub - at a set height, or growing in a particular direction - you need to prune it. But unless you're shearing a hedge or sculpting a boxwood into topiary, you don't want to use hedge trimmers. To get a natural look, you want to prune more carefully, taking each branch and aiming for the appearance of randomness. You may also want to thin the plant so that it gets more air and grows fuller rather than taller.

You may also prune for plant health. For example, maybe you've had some disease problems on part of a tree or shrub, or the plant is getting leggy (not so many leaves at the base of the plant). When small trees and shrubs are dense in the middle, they often develop branches that cross each other and rub. That rubbing can damage the bark and let diseases and insect pests in. So it's best to prune them so that each branch doesn't touch any other branch.

With some shrubs you may want to do what's called renewal pruning, in which you remove old branches right down to the ground so that vigorous new branches can grow; this may promote better branch color (for example on red-twig dogwoods) or more flowering (well sited old lilacs benefit from renewal pruning.)

So: this leaves you with a lot of questions. When do you prune a particular tree or shrub? How do you prune?

Check your tools. Your pruners should be clean and sharp. Make sure you are using bypass pruners, not anvil pruners. Anvil pruners may crush the wood, resulting in a jagged cut and allowing diseases in to the plant. Clean the pruners with rubbing alcohol and sharpen with a whetstone. Your saw likewise: clean the blade with steel wool, and replace it if it's dull. If you are going to be pruning diseased branches, bring along a jar with some rubbing alcohol in it, so you can wipe off your tools after the cuts.

The most important rule of pruning is to take your time. Walk around the plant and look at it carefully. Notice any diseased or infested branches, crossing branches, or branches that are drooping or shooting straight up. Think about how you want the plant to look. Have a purpose in mind.

Begin by pruning out dead, weak, and diseased wood. Remove suckers (shoots coming up from the ground) and water sprouts (small branches growing straight up from an older branch). Next remove crossing and rubbing branches.

With young trees, 1-3 years after planting, you might want to prune to develop a strong scaffold pattern. Stagger lateral branches out from the trunk for good stability. With trees that will be 40 feet or more tall at maturity, space the laterals about 18 inches apart. For smaller species, space the laterals at 6 - 8 inches apart. You want to prune for a strong central leader, so prune back shoots that are too close or too vigorous in relation to the central leader. Prune for wide crotch angles: they make for a more stable tree.

As you work, think about directing new growth outward or into areas that need filling. Take your time. Step back periodically and determine if the tree or shrub is keeping its natural form, remaining balanced and full looking.

Pruning cuts: You can cut small branches (less than 1" in diameter) with pruners. Anything bigger will need a saw. I have a folding pruning saw that I like a lot. When you're pruning trees, prune at the crotch. Notice at the intersection of branch and trunk how there's a branch collar that forms a swelling at the base of the branch and produces a ridge above the branch Locate your cut so that the entire collar stays on the trunk, but you don't leave any stub protruding. If the branch makes a wide angle with the trunk, you can safely cut down. If it's a tight angle, cut up. If it's big, you may need to make several cuts: The first cut goes up from the bottom of the branch and several inches out from the crotch. Cut up about 1/3 of the way, or until the saw nearly binds. Make the second cut through the branch two or three inches beyond the first cut. This ensures that a heavy branch won't tear break away from the trunk as it's being cut. Then you can make your final cut just outside the branch bark ridge and the branch collar.

On shrubs, the rule of thumb is to cut to a bud. If you want to direct the plant's growth, consider that the direction of the bud will be the direction of the new shoot. Cut at an angle, leaving as little stub as possible past the bud. This enables the plant to heal faster. It also stimulates lateral growth. If you have a shrub that is getting tall and leggy, cut back the tallest branches to a lateral bud, and that should help redirect the growth and produce more flowers to boot. Some shrubs as they get older produce smaller flowers; if you prune them, you may be able to encourage the plant to produce more and larger flowers.

The trick with shrubs is knowing whether they bloom on new or old growth. Quickly, though, here are a few flowering shrubs that you should prune in the spring, since they bloom on new growth:

Buddleia davidii - Butterfly Bush
Callicarpa species - Beautyberry
Caryopteris - Bluebeard
Hydrangea arborescens - The big mophead Hydrangea
Potentilla
Most shrub roses

For plants that bloom in the spring, such as lilacs and forsythia, the best time to prune is right after flowering. Then your job is just to shape, prune for health, and clean up the dead heads, to promote more flowering next year.

Finally, a couple of points about pruning evergreens: Never cut beyond the green foliage. The plant will not regenerate. If you're hedging evergreens - yews for example - make the shape slightly wider at the base than at the top to let light reach the leaves at the bottom of the plant. This will help prevent the plants from becoming leggy and unattractive. Prune evergreens now. Yesterday. Cut them back to a bud, and never remove more than about 20% of the plant. Evergreens will not recover if you cut them back too hard.

I can't give you an exhaustive list here, so your best bet is to search your university extension's web site or buy the best book on trees and shrubs, Dirr's Hardy Trees and Shrubs, by Michael Dirr.

OK, have I got you totally confused? Honestly, I think it's smart to consult an arborist if you don't know what you're doing. Or even if you do. If it's a matter of keeping your shrubs tidy, you can do that yourself, but unless you're a daredevil or a cat, don't go climbing trees. If you take two things away from this blog let it be these: cut shrubs to a bud, and cut back the ones that flower on new wood now.