How to Trim Flowering Shrubs

Your clematis was a knockout, your hydrangeas were absolutely poetic, and the lilacs--ah, the lilacs! Last year was wonderful and just the way it should be every year. Learning to prune is an essential part of repeat performances from your woody shrubs.

Difficulty: Moderate

Instructions

Things You'll Need:

• pruning shears or long-handled loppers
• pruning saw for large woody shrubs
• heavy garden gloves
• good advice--garden book, garden websites, experienced gardener, experienced nurseryman
• trash bag for clean-up

How to trim flowering shrubs

1. The best time to get pruning advice is while your shrubs are still in bloom. Especially if they are well-established or large--or both--you need to prune each at the best time for it. Some flowering shrubs set next year's blooms on new growth (a rhododendron, for example, begins sending out new flower-stems and supporting leaves right after blooming--new buds ride out the fall and winter already formed on the bush). Some wait till the following spring to send out that new growth; others will bloom on both old and new growth. You need to know what your shrubs do so you can help them bloom well again.

2. Second, find out how much to prune. Some, like viburnum or andromeda, can be cut to the shape you desire and will bloom well more or less whenever that is done. Others will show much less bloom if pruning is concentrated only on the outer shape--remember that every woody shrub has to put spring strength into the wood as well as the flowers.

3. Rhododendrons and lilacs, among others, grow best when you prune-by-threes: during year one, you select the oldest, thickest third of the branches and trim them back to ground level. In year two, select the oldest, thickest third, trim to ground level. Year three--you guessed. Learn to sleep through the conviction that you've just killed a large and established planting. After all, if you had just re-shaped your shrub from the outside, you'd have cut off all next year's flowers.

4. Following directions, prune away. Ask whether to fertilize afterward. Whether you fertilize or not, water some extra for a couple of weeks--pruning is a milder shock than transplanting, but a shock all the same.

5. Put all pruned branches into trash bag, especially if they look diseased. Leaving them under the shrub can spread disease, if any, and hamper healthy growth.

Tips & Warnings

• Everyone reacts to pruning the same way: "I've killed it!" It's rare that you will and worth the gamble. Shrubs no longer burdened with heavy, dead wood or diseased branches now have more energy to flower. You'll be gratified and perhaps astonished at new spring growth (and it's okay to trim a new shoot or two if the shape is really getting out of control).
• Spending extra time getting good advice is worth it. Most gardeners are generous with advice and experience--if you find one who is not, move on till you get advice. Websites specific to your shrubs often give excellent advice--you may have to look up several kinds of shrubs, but it's better than being confused by generalities.