Hydrangeas add beauty to any landscape. They have attractive foliage and produce large, striking blossoms. Hydrangeas are also hardy, insect, and disease resistant, and versatile. They grow well in a variety of soils and tolerate wetness better than most other woody plants. One drawback is that different cultivars require different pruning styles and many gardeners don’t know how and when to prune them.
Hydrangeas that bloom on old wood from last year’s growth are the earliest to flower – before July. Those that bloom later in the season – after July – are flowering from blossom buds on new wood that is growing during the current year.
If you feel uncertain about which variety you have, a safe rule for all types of hydrangeas is that no pruning is better than the wrong type of pruning.
A simplified approach, suitable for all types of hydrangeas, is to limit pruning to:
- Winter-killed wood — Remove all dead branches in the spring before or as the buds are opening. Test the stem for life by scraping the bark with a knife. If it’s not green underneath, it’s dead and should be removed.
- Rejuvenation — Old wood dies back on even the healthiest hydrangeas. In the early spring remove dead or very old stems by cutting them at the base of the plant. This will stimulate new growth and produce a more vigorous bloom set later in the summer.
- Dead flowers —Removal of old dried flowers, known as dead-heading, is the safest pruning and can’t be done incorrectly.
Types of hydrangeas and tips on pruning
1. Bigleaf hydrangea, H. macrophylla
This is the most commonly grown hydrangea in Maryland. It has attractive, lustrous leaves and large blue, pink, red, or purple flowers. These hydrangeas include two forms: the mophead and the lacecap types. Both are pruned the same way. This group of hydrangeas also includes the repeat bloomers, which bloom on both the old wood from the previous year and on the current season’s wood. A popular cultivar of the repeat bloomers is ‘Endless Summer' but there are many newer repeat blooming cultivars available in the trade.
Sometimes bigleaf hydrangeas become overgrown and need to be trimmed. However, too much pruning will greatly reduce or eliminate flowering. It’s best to wait until new growth emerges in the early spring to be sure that you are only removing dead or weakened parts and not removing live stems with flower buds. In very old and declining hydrangeas, hard renewal pruning may be needed. Cut back all of the branches to the ground. This will eliminate the blossoms for that year but the next year should be quite productive.
Some popular cultivars of merit in the species macrophylla include: ‘All Summer Beauty,’ ‘Altona,’ ‘Dooley,’ ‘Europa,’ and ‘Nikko Blue.’ However, new cultivars are introduced into the landscape trade every season.
The flower color of the macrophylla species is dependent on soil pH. A pH below 6.5 will produce blue flowers and a higher pH will produce pink or red flowers.
2. Smooth hydrangea, H. arborescens
Native to the North American woodlands, it is fairly common in home landscapes. This species blooms with white flowers on new wood of the current season, making it the easiest to prune. Simply cut it back hard in early spring. Flowering is actually enhanced by cutting back all stems to about 12 inches from the soil line. Well-known cultivars include ‘Annabelle’ and ‘Grandiflora.
3. Pee Gee hydrangea, H. paniculata
Originally from the Orient, this is one of the largest hydrangeas. It can reach 25 feet high. It has brittle stems that may break under a load of white blossoms in windy weather or under heavy snow. Remove broken stems as they occur to keep the plant healthy. Like the smooth hydrangea, it also flowers on the current season’s wood. Pruning in the spring will actually enhance flowering as well as help to manage its size. If the size is of no concern, simply remove spent flowers and any broken stems. Cultivars of merit include ‘Barbara,’ ‘Bridal Veil,’ ‘Brussels Lace,’ ‘Chantilly Lace,’ ‘Grandiflora,’ and ‘Limelight.’
4. Oakleaf hydrangea, H. quercifolia
The oakleaf hydrangea is a beautiful native of the southeastern United States and is a favorite of many gardeners. Its foliage is spectacular even without the massive, upright, 12-inch blossoms. Its flowers are produced on old wood from last year’s growth. In Maryland, it blooms in June, but the flowers persist through the summer and gradually change from white to pink, and eventually to a tan color in the winter. If needed, prune after flowering to maintain a desired size and shape. Winter-killed or other deadwood can be removed at any time.
5. Climbing hydrangea, H. anomala subsp. petiolaris
This trailing-vine species is a vigorous grower that is attractive and easy to maintain. The only pruning needed is to remove unwanted stray stems to control their growth. This may need to be repeated several times in the season as the vine quickly produces new stems. In central Maryland, it flowers in April and May on old wood from the previous year. To avoid reducing bloom, prune them after blooming.
Author: Raymond Bosmans, Professor Emeritus, University of Maryland
Editor: Jeanine Smetana, University of Maryland Extension Master Gardener
Adapted from an article in the May-June 2010 HGIC E-Newsletter