Hydrangeas in Winter
Hydrangeas are popular garden shrubs because of their fist-sized, often multicolored blooms. Several hydrangea species are available and these vary in their tolerance of extreme weather conditions. Gardeners interested in adding this shrub to their collection should consider how best to protect it during the winter months
Hydrangeas vary in their ability to undergo winter weather extremes. Bigleaf or mophead hydrangeas--one of the most common species, producing large pink and blue blossoms--need winter protection, otherwise some of the stems will die back in the cold. Annabelle and panicle hydrangeas tolerate winter weather in most of the United States and Canada.
According to the U.S. National Arboretum, winter damage is the most common reason why bigleaf hydrangeas fail to bloom. These plants break dormancy in the late winter or early spring, when a spell of warm temperatures cause leaves and buds to resume growth. When temperatures plummet again, this tender new growth dies, sometimes killing an entire branch. Low winter temperatures and late spring freezes pose the greatest risk to bigleaf hydrangea, and the National Arboretum does not recommend growing this species in hardiness zones colder than zone 6.
On her website Hydrangeas! Hydrangeas!, hydrangea enthusiast Judith King recommends several strategies for protecting hydrangeas from winter damage. The easiest method involves circling the plant with four or five wooden stakes and wrapping it with chicken wire. Fill the enclosure with dead leaves or pine needles to provide insulation. Oaks leaves, especially, work well because they will not mash down. Other gardeners cover their plants with a sheet or other covering, but King reminds her visitors that winter winds may cause the covering to rub developing flower buds, damaging the plant and inhibiting blooming.
One of the advantages of container gardening is the ability to bring tender plants inside for the winter. Hydrangeas can grow in containers, if given adequate room for their voluminous root systems, enabling you to bring sensitive species indoors before temperatures plummet.
Pruning hydrangeas helps to prepare them for winter and recover their good looks if they sustain winter damage. The U.S. National Arboretum recommends pruning bigleaf hydrangea after they finish flowering in the fall. Other species that produce new growth each year for flowering can be pruned until early spring, before leaves appear. Pruning helps to keep the plants compact so that they are easier to cover and protect. In the spring, if branches aren't showing any signs of life, they were likely damaged by winter weather and need to be removal.
As Judith King points out, hydrangeas grow to be large plants. If you live in an area where they will likely sustain winter damage, the practicality of enclosing an enormous shrub each fall bears consideration. If you don't want to go through the trouble, consider one of the hardier, less common varieties that will better survive the winter.