1.) For hydrangeas remove all dead stems. After the plant is about 5 years old, remove about a third of the living stem to revitalize the plant. Otherwise, leave the plant alone and let it grow big. If the hydrangea becomes too large, make sure to prune it after the flowers have bloomed to avoid removing the buds.
2.) Old vs. New wood? New wood are stems and branches produced during the current growing season. Old wood is produced during the years before. Traditional hydrangeas bloom on new or old wood; Endless summer hydrangeas are the exception because they bloom on both new and old wood, making them foolproof for pruning whenever you get the notion.
3.) Mopheads, lacecaps and oakleaf hydrangeas bloom on old wood, so prune them before August during the summertime, when they begin to develop next year’s flower bud.
4.) PeeGees and Annabelles can be pruned in fall, winter or spring because they bloom on new stems. White blooming Annabelles can be pruned back within a few inches of the ground in the winter. This annual pruning can weaken steams that must hold up huge flowers, so plant the shrubs close together so they can support one another.