Winter 2016 will not be remembered for an abundance of snow, cold temperatures, or massive storms. Average temperatures for this past winter were more than 6 degrees warmer than in previous years, placing winter 2016 among the five mildest winters on record. But every winter has its coldest days and for us in New England, the February cold snap came in fierce and hard.
Plants start to grow in response to warmer temperatures and longer periods of sunlight. They can get fooled by warmer periods that come too early. If plants start to bud and begin casting off their winterized protections and then are suddenly hit by freezing temperatures, buds may be damaged and flowering will be affected. That’s what happened to some hydrangeas and other flowering plants in New England.
Hydrangeas are not the most winter-hardy plants. Mild periods between cold snaps can be detrimental to many plants. Unfortunately, there is not a lot you can do about it. Since most hydrangeas set their flower buds before they go dormant, an inconsistent winter can damage the buds, and the plant will not bloom. This season we have also seen this pattern with the magnolias and forsythias, and in turn some plants really struggled to bloom.
Plants that bloom on old growth are the ones hurt by these fluctuating mild winters. Lilac, viburnum, and hydrangea fall into this category. Hydrangeas, however, can be especially tricky because not all varieties flower the same way. There are two distinct types of hydrangeas: one that produces flower buds on stems of “old wood” and another type that produces blossoms on stems of “new wood.” Stems are considered “old wood” if they have been on the plant since the summer before the current season. “New wood” blooming hydrangeas develop stems and buds during the current season.
The big, showy blue blossoms of old-fashioned hydrangeas—the mopheads, lacecaps, and oakleafs—all flower from old growth. “Old wood” hydrangeas start developing their buds in August or September. It is not beneficial to prune these plants in the fall, for you would be taking off next summer’s flowers.
Generally speaking, you should not prune spring-blooming shrubs more than a month or so after they finish blooming. After flowering, you should prune immediately, or you should pick as many of the flowers as you can while the flowers are blooming. Who doesn’t love vases of hydrangea or lilac?
The “new wood” bloomers are a little bit more rugged and bloom every year regardless of how they are treated. They can be pruned all the way to the ground in the fall and emerge in the spring with fantastic blooms. Pee Gee and Annabelle hydrangeas fall into this category.
Woody plants that flower late in the season bloom on new wood. A nice rule of thumb is that if you go outside in early spring and you don’t see any buds, you are safe to prune. Buddleia and weigelas fall into this category.
The one exception to the rule is the Endless Blooming hydrangea. The “Endless Summer” variety produces flowers on both the new and the old growth. It blooms on old growth in the spring and new growth in the summer.
Roanne Robbins, a former Harvard resident
and an avid gardener, lives in Maine.
