Enthusiastic, flower-covered hydrangea bushes require little care in the winter; they simply slip into dormancy and await the return of warm weather. However, ensuring that your hydrangeas are ready to be at their best when spring does come back around is as simple as one, two, three.
Prune back any dead, diseased, or damaged stems from the hydrangea bush in the fall. Remove or cut back by 1/3 all the stems that bore blossoms in the summer. Improve the strength of the bush by cutting off any straggly or overlong stems, or weak shoots.
Spread a thick layer of mulch all around the base of the hydrangea bush.
Fertilize in late winter by raking back the mulch around the hydrangea and sprinkling an organic fertilizer on the soil. Check the fertilizer package for instructions about how much fertilizer to use. Rake the mulch back over the fertilized area and water the hydrangea well.