(Carol O'Meara / CSU Extension)

Warm days woo us to get out and get some fresh air, puttering around the yard to take note of winter's toll. We tell ourselves we're just going to peek at the garden to see how' it's doing, but once under the spell of balmy temperatures, we can't help but want to do something to it.

Resist. And if you can't resist, then take the time to prune some shrubs.

Woody plants suffering snow damage, needing a canopy thinning, or renewal from old age will benefit from a nice haircut, but clipping a plant that needs pruning can be a little daunting. With branches going everywhere, many gardeners freeze up, not knowing where to start. They nip in fits and starts, often with little effect at all. Others dive in with gusto, giving the poor shrubs a buzz cut with a hedge trimmer.

If you're in the latter group, lean close so I can stare you in the eyes when I say: Please don't do this. Hedge trimmers can leave a nightmare of split ends and exposed stalks bad enough to take half the summer to cover, and with woody plants, there are no comb-overs for the bald spots.

What stays and what goes?

To preserve a shrub's natural form and health, it is important to keep a few tips in mind when pruning. Spring-flowering shrubs bloom on new wood that grew the previous summer. Buds for spring flowers developed in mid-summer through fall last year, and shearing the plant before blooming may result in chopped off flowers. Instead, if the plant is overgrown, it should be thinned by removing older canes to the ground. This allows sunlight to penetrate into the center of the plant, where there will be better flowering throughout. Thin no more than one-third of the plant each year, and thinning should be done before active growth starts in spring.


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Summer-flowering shrubs bloom on new wood from the current growing season. Thinning in the early spring before growth starts is an ideal approach to pruning summer-flowering shrubs. On shrubs where the bark provides color, such as red-twig dogwood (Cornus sericea), the best color is from new growth, and pruning canes to ground level in early spring stimulates the plant to put up new, colorful canes.

Start simply by removing any broken or competing branches; often this thinning reveals other places that need a trim. Competing branches are those that rub against one another or block other shoots. This rubbing causes wounds in the bark that allows disease to enter. Prune one branch off to allow room for the other to grow.

Once this is completed, stand back and look over the plant to see if the pruning for health has left the plant misshapen, and consider what other cuts will help the plant maintain its form. Pruning is not a race, and gardeners who flail about with a sharp tool and no plan can expect to have startlingly awful plant shape. Consideration of the plant's form is as important as the cuts themselves.

Removal of up to one-third of the plant is fine; more than this and you could set the plant's growth back. Remember, go slow. There are more warm days ahead of us and you can clip a few branches here and there as spring approaches. But the real art is knowing when to stop pruning, so step back after each cut and assess the plant.

Carol O'Meara is the extension agent in horticulture entomology for Colorado State University's Extension in Boulder County. Contact her at comeara@bouldercounty.org.