Answer: The bigleaf hydrangeas (Hydrangea macrophylla) bloom on old wood from the year before. Pruning in spring removes flowering wood and limits blooming as a result. Winter cold damage to the stems, and frost damage to the new growth or buds in early spring will also limit flowering.
These hydrangeas may be pruned in summer right after they bloom to thin them or if necessary to control size. In spring, you may have to prune to remove winter-killed dead branches but be very patient and be sure they are truly dead before you cut them off.
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