Avoid too much shade and too much nitrogen

Two words to remember when it comes to hydrangeas that refuse to flower are “too much.” Bigleaf hydrangeas grow well in the shade in most areas of the United States; however, too much shade can result in gorgeous leaves and no flowers. The high shade created by deciduous trees or evergreens is perfect for bigleaf hydrangeas in the East, Midwest, and Northwest. In California, any shade you can find, as long as it is not too dense, seems to work. But hydrangeas located near a foggy coast and in northern areas of the country require no shade at all.

Another problem could be too much fertilizer. A high-nitrogen fertilizer will result in beautiful leaves and few, if any, flowers. Bigleaf hydrangeas can tolerate very high levels of fertilizer without showing signs of fertilizer burn, so practice moderation. Too much water and too much dryness can also result in a lack of flowers.

Basics

Hydrangea macrophylla and serrata cvs.

ORIGIN: These deciduous woodland shrubs are native to Japan. There are more than 400 known cultivars between the two species.
HARDINESS: USDA Hardiness Zones 5 to 9. They do best in full sun to partial shade, depending on your location.
CONDITIONS: They prefer moist, well-drained soil but can develop yellow leaves, a symptom of chlorosis, in highly alkaline soils.
PROPAGATION: Propagate new plants by softwood or semi-hardwood cuttings taken in late spring or early summer.
PRUNING: Prune dead wood from shrubs in early spring. Avoid pruning the previous year’s healthy growth, since flowers develop on old wood.
SIZE: Plants range from 3 feet to 6 feet tall, but wind and cold temperatures can cause injury and hinder overall shrub size.

See our gardening basics project guide.

Choose from a number of proven cold-hardy varieties

Many bigleaf hydrangea cultivars make it to garden centers or into mail-order catalogs before being tested for cold hardiness in the landscape. That’s why researchers like Sandra Reed, research geneticist at the United States National Arboretum, and the staff at North Carolina State University’s Mountain Horticultural Crops Research and Extension Center, in Fletcher, have been evaluating hundreds of cultivars for cold hardiness. After five years of research in test plots in Missouri (Zone 5), Tennessee (Zone 6), and North Carolina (Zone 7), these are the selections we found to have the most consistent flowers for areas with cold winter temperatures. All are hardy in Zones 5 to 9.

Proper placement is a key to flowering

If you’ve met all of the cultural needs of your hydrangea and you’re still not getting flowers, understanding how its flower buds are produced may help. On bigleaf hydrangeas, the flower buds form on the previous year’s growth, known as old wood. Therefore, destroying or removing these flower buds will keep your plants from flowering.

Bigleaf hydrangeas require very little maintenance pruning other than removing deadwood from the shrub in early spring and possibly deadheading the flowers for aesthetic reasons. Any pruning of healthy growth in the spring, fall, or winter (including help from browsing deer) is likely to result in reduced flower production. If you have to prune your hydrangea to control its size, the only time to cut back healthy growth is in summer immediately after the shrub has finished flowering.

Cold winter temperatures can often kill off flower buds. This problem can be addressed by planting bigleaf hydrangeas on north- or east-facing slopes rather than toward the south or west, which are the first areas to warm up in late winter, triggering buds to open too early. Choosing cold-hardy varieties and siting plants under a canopy of evergreen trees can help to avoid winter kill. Some people apply a temporary deep layer of winter mulch to protect lower buds from cold temperatures. I’ve also seen gardeners successfully protect their plants by wrapping them in a burlap cocoon each winter. However, in regions with variable winter temperatures, protection may provide only limited help. During brief late-winter warm spells, when the flower buds are triggered to break dormancy, they are then often killed by returning cold temperatures. In this instance, there’s not much you can do other than practice these protective measures and hope for Mother Nature to cooperate.

With a better understanding of how these plants grow and by choosing selections that stand up to the cold, the odds of having outstanding performers are considerably stacked in our favor.