Hydrangeas produce showy blossoms on new growth each spring and summer. Unexpected frosts in the early fall or late spring can kill that new growth and prevent the plant from blooming. Frosts can also freeze old, strong growth and weaken the plant. The best way to care for a frozen hydrangea is to protect it from further damage and give it time to recover.
Cover the hydrangea with an old sheet if another frost is coming. The sheet will protect any growth that survived the last freeze. Remove the sheet when the threat of frost passes.
Allow the hydrangea to drop damaged leaves on its own. Damaged leaves are a brown color, and may look shriveled. Once the plant drops the leaves, rake them up and dispose of them in the trash or compost.
Water the plants two times a week, if there is not an equivalent amount of rainfall. Water enough during each session to thoroughly soak the soil.
Apply a slow-release, general-purpose fertilizer to the soil around the plant, according to the package directions.
Prune the plant no sooner than the next growing season. Remove any branches that do not bloom with garden shears, as this is the growth that did not recover from the last year’s freeze.