Know when, how to prune hydrangeas

One of the more frequently asked questions that I receive is when to prune shrubs. This can be easy or hard to answer because of the many types of shrubs that we grow in this area.

//

Another factor is whether the plant flowers. Shrubs grown mainly for their foliage are easier to prune, because you don't have to worry about reducing the number of flowers . Most shrubs that are grown for their foliage are pruned in late winter and early summer 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. T he more new growth that you have, the more flowers you will have. There are several shrubs in our landscapes that we prune this way. One of the more common plants we prune this way is the crape myrtle. You can deadhead the flowers on crape myrtles and they will bloom a second time.

The shrub that I am going to discuss today is the plant that I have the most questions on how to prune: the hydrangea. How and when to prune hydrangeas is an issue for many gardeners, even those with experience. The question we need to ask is why do we prune hydrangeas? Pruning is done to reduce plant size or to reshape the plant; to remove old, non productive branches; to remove frost-damaged leaves; or to deadhead blossoms. So, when do I prune my hydrangea?

There are five popular types of hydrangea that are planted by gardeners. I will discuss when and how to prune each of these types. Some of our hydrangeas bloom on new wood and some on old wood, so you need to know which type of hydrangea you have.

The most common 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 wood. Prune after blooms begin to fade in July. You need to have all pruning done by August 1 so that the new growth will have a chance to harden off before cold weather. On a mature bush, five to six years old, you need to remove one-third of the oldest woody stems each year. Usually, these stems are in the center of the plant. In the spring , you can 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 you need to prune after the blooms start to decline. Again, you need to prune one-third of the old plant material 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 two buds at the base of each stem. The second option is not to prune , 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 , 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 last major hydrangea is the climbing hydrangea, Hydrangea anomola petiolaris. This hydrangea needs little or no pruning. In the summer, you can remove unwanted shoots that have grown where you don't want them to grow.

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. If your hydrangeas still won't bloom, you need to look at other factors such as too much shade, over-fertilization or cold damage to the blooms.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/columbia.