The Best Time to Prune Flowering Shrubs

The most common mistake people make when pruning flowering shrubs is doing it at the wrong time. Pruning at the wrong time of the year won't usually hurt your plant, but pruning at the right time can help improve flower production. Although each flowering shrub has its own requirements, here are some general guidelines to follow when trying to determine the best time to prune.

Why Bother Pruning?

Most flowering shrubs need very few touch-ups with the pruning shears. One of the main reasons to prune them is to help guide their natural growth. Pruning encourages flower and fruit production and allows more light and air to reach the inner branches. An occasional polite shaping will help them maintain a pleasing, healthy form, and will usually be rewarded with a prolific amount of blooms.

You should never need to prune your flowering shrubs more than once a year. Flowers take a long time to form, so if you continue to trim them every few months you will increase your chances of removing future blooms. Always use sharp, clean tools when pruning. This will prevent injury to branches and minimizes the risk of introducing disease.

Flowering Shrub Type #1: Blooms on new wood.

Flowering shrubs that bloom on new wood usually don't bloom until after June and are considered "late-flowering". These shrubs spend the first part of the season producing new wood, and the second part of the same season flowering. They should be pruned in late winter or early spring before the new growth starts. An example of this type of shrub is Mock Orange.

• If your flowering shrub blooms in the summer or fall, prune it anytime between leaf-drop in the autumn and late winter. Then the shrub will have plenty of time to form new buds before it flowers.
• Plants that are less cold tolerant should be left until late winter, as a network of intact branches can help trap air and leaves to create a bit of winter protection.

Flowering Shrub Type #2: Blooms on old wood.

Flowering shrubs that bloom on old wood usually bloom earlier in the season. Examples of this type of shrub include forsythia and lilacs. These shrubs produce flower buds along their stems during the preceding autumn, and should be pruned immediately after they bloom so that they can spend the rest of the season focusing on new growth.

• If your flowering shrub blooms in the winter or spring, prune it as soon as you can after the flowers fade. If you use the shrub for cut flowers (like lilacs), you can also prune lightly as it is blooming.
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• Another trick with flowering shrubs such as lilacs is to deadhead them-remove the spent flowers after blooming. This not only puts more energy into plant growth but counteracts the tendency of some shrubs to flower and fruit heavily only in alternating years.