There are many types of hydrangeas, from the mophead to the old-fashioned tree forms to the climbing hydrangea, all with different degrees of hardiness and cultural needs; hence there is no one-size-fits-all approach to winter care. Preparing your hydrangea for winter involves knowing which type of hydrangea you have, whether it blooms on last year's growth (old wood), on new wood or on both, how it tolerates cold and whether you need to protect buds from freeze damage.
Bigleaf Hydrangea: Mophead and Lacecap
Most mophead and lacecap varieties (Hydrangea macrophylla) bloom on old wood, making their winter care a little more crucial. Freeze damage to nascent flower buds can result in fewer or no flowers later. According to Wilkerson Mill Gardens in Georgia, winter care involves preparations for the cold months and for the weather vagaries at winter's end. Wilkerson Mill Gardens recommends protecting the plants with evergreen branches or straw, or wrapping burlap around them. If a late winter freeze is expected, spread a blanket over the plant.
Re-Blooming Bigleaf Varieties
According to Proven Winners, a grower that supplies retail outlets, re-blooming hydrangea varieties bloom on old wood as well as new and there is no need for concern if the buds suffer freeze damage; they will still bloom on the new growth. Kerry Smith, a horticulture associate writing for Auburn University, is more definite about bloom times. Re-blooming varieties, Smith says, bloom twice a season: in early summer and fall. Hydrangea macrophylla varieties come in shades of pink, blue and white and are hardy in USDA Hardiness Zones 6 to 9.
Oakleaf and Climbing Hydrangea
Oakleaf hydrangea (Hydrangea quercifolia) has oak-shaped leaves and white conical flowers. It blooms on old wood and may need protection for the winter. Wilkerson Mill Gardens recommends protecting this hydrangea if winter temperatures can go to -20 degrees F. It is hardy in USDA Hardiness Zones 5 to 9.
Climbing Hydrangea is a vine with white lacecap style flowers that bloom in spring, also on old wood. It is a strong vine that self-attaches to walls and trees. It rarely needs winter protection. It is hardy to USDA Hardiness Zone 4.
Pee Gee Hydrangea and Annabelle
Pee gee hydrangea (Hydrangea paniculata) and smooth hydrangea (Hydrangea arborescens) bloom twice a season on new wood and winter care is rarely needed for these varieties. The pee gee can be trained into a tree-form.
Kerry Smith lists a variety of smooth hydrangea called hydrangea grandiflora as the hardiest of the hydrangeas. Annabelle is another smooth hydrangea that is shorter and more popular with gardeners. These varieties are hardy to USDA Hardiness Zone 3.
Optimizing the Health of Your Hydrangea
Hydrangeas have different cultural needs and when met, the plants will fare better through the winter. According to Kerry Smith, most varieties prefer a morning sun situation and moist soil with organic amendments. The mopheads and lacecaps prefer more water. The pee gee hydrangea can take more sun. Fertilizing, for the most part, should be light, however the mopheads, lacecaps and reblooming varieties prefer three applications during the season.