Pruning will get best results when done in late winter or early spring

When do I prune my plants? This is one of the more misunderstood aspects of gardening because of the many types of shrubs that we grow.

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Another factor is whether to plant flowers. Shrubs grown mainly for their foliage are easier to prune and it is easier to determine when to prune them, because you don't have to worry about reducing the number of flowers produced. Most shrubs that are grown for their foliage are pruned in late winter or early spring, and then are pruned as needed during the summer. When it comes to shrubs that produce flowers, it becomes a little more complicated.

Shrubs that flower will either bloom on new wood or old wood. Shrubs that bloom on new wood need to be pruned late winter or early spring. This will encourage new growth. Therefore, the more new growth you have, the more flowers you will have.

There are a number of shrubs in our landscapes that we prune this way. One of the most common is the crape myrtle. You can deadhead the flowers on crape myrtles and they will bloom a second time.

Plants that bloom on old wood need to be pruned after they flower. A good example is azaleas. Most spring flowering shrubs set their flower buds in midsummer, so any pruning that you do after midsummer will remove flower buds. Therefore, you will have a reduction in the flowers next spring.

The shrub that I have the most questions on how to prune is the hydrangea. How and when to prune hydrangeas is an issue for many gardeners, even those with experience. Pruning is done to reduce plant size or to reshape the plant; to remove old, nonproductive branches; to remove frost-damaged leaves; or to deadhead blossoms.

There are five popular types of hydrangea that are planted by gardeners. Some of our hydrangeas bloom on new wood and some on old wood, so you need to know what type of hydrangea you have.

The most common and favorite hydrangea is the bigleaf -- Hydrangea macrophylla. There are other names that this plant goes by, such as French hydrangea, mop-head hydrangea, and common or garden hydrangea. This hydrangea blooms on last year's or old wood and should be pruned after blooms begin to fade in July. However, all pruning should be done by Aug. 1 so the new growth will have a chance to harden off before cold weather.

On a mature bush, 5 to 6 years old, remove one-third of the oldest woody stems each year. Usually, these stems are located in the center of the plant. In the spring, remove old or dead branches.

Oakleaf hydrangea -- Hydrangea quercifolia -- is a large shrub that should be left to grow in its natural form. The oakleaf hydrangea blooms on old wood, so it should be pruned after the blooms start to decline. Again, one-third of the plant material should be pruned to increase sunlight and air circulation. If necessary, you can prune back to one or two buds on a stem. This should be done in early spring to renew overgrown plants. When you prune in this manner, you will not have any flowers for that year.

Peegee, Hydrangea paniculata "Grandiflora" and smooth, Hydrangea arborescens "Annabelle" hydrangeas bloom on new wood. Around the first of March, you can prune these plants severely to leave only two buds at the base of each stem. The second option is not to prune the plant, and you will still get new growth and flowers. If you prune severely, the plant will be smaller but will have larger blooms. If you don't prune the plants, you will have larger bushes, but smaller flowers. The Annabelle hydrangea needs to be pruned back 6 to 12 inches from the ground each March.

The climbing hydrangea -- Hydrangea anomola petiolaris -- needs little or no pruning. In the summer, you can remove shoots that have grown where you don't want them.

If you know the type of hydrangea that you have, you should be able to follow these simple guidelines on when to prune in order to get more flowers. However, if your hydrangeas still won't bloom, consider whether they have too much shade, over-fertilization or cold damage to the blooms.

Reach Columbia County Extension Agent Charles Phillips at (706) 868-3413 or charlesp@uga.edu. The Extension site is www.ugaextension.com/columbia.