Pruned large, healthy hydrangea bushes in Jan 2013. Plants have grown significantly and look healthy but no blossoms this summer. When should we prune to have blossoms next year? How heavily to prune? Bushes would be too large next year if not pruned. (Plants are probably bigleaf type - originally purchased at nursery in western Oregon.)
Prune hydrangeas and most other spring-blooming woody ornamentals shortly after they have bloomed. Most bloom on "old wood." If you prune a hydrangea in Jan. you will cut off the flower buds for the coming spring. This year, prune after other hydrangeas in your neighborhood have mostly finished blooming or in early fall. To help control the size it is best to prune by taking out some of the oldest main branches clear to the base. To keep a plant heathy it is best to not remove more than about 1/3 of the plant in a given year. If you just prune the edges, the plant will get bushier as time goes by and you will not have controlled the overall size much. You will have just made more branches that are smaller/weaker, which then produce smaller/weaker blooms.