Hydrangeas pruning methods can be divided into two types, based on their different blossoming modes:
The first pruning method is suitable for bigleaf hydrangea (excluding 'Endless Summer', a variety that blooms on both old and new branches) and oakleaf hydrangea. These two hydrangeas bloom on old branches and have relatively strict requirements on pruning time, usually only in early summer, and no later than late summer. In late spring, they are blooming or going to bloom, and flower buds start to form or develop from late summer to the following spring. Daily pruning is required to cut off withered flowers and dead, weak, and inward-growing branches.
These hydrangeas have a distinctive feature: new branches will form on two buds adjacent to a cut. Buds that are lower then become almost undeveloped or grow poorly due to the lack of apical dominance. Therefore, pay attention to whether there are buds under the cut, as well as the height of branches and directions of buds. They have opposite branches, so the directions of reserved buds should be decided by the specific shape of the plant. Additionally, when plants are too large, they can be pruned heavily in summer. The part above the ground should be kept at about 15 cm high. This way, there will be a new, small plant at the end of the year, and it will not affect blooming next year.
The new branches of 'Endless Summer' bigleaf hydrangeas will bloom. Therefore, there are no strict requirements on pruning time; just avoid pruning in spring when buds are formed. Pruning during the rest of the year does not affect flowering, and plants are usually pruned in winter after the leaves fall.
The second pruning method is suitable for smooth hydrangea and panicle hydrangea. These two hydrangeas bloom on new branches grown that year, so there is a large window for pruning. Blooming will not be affected by pruning in all seasons except during spring budding. The only existing smooth hydrangea is the Annabelle series. After its leaves fall in winter, the parts of Annabelle above the ground can be completely cut off. However, this results in one disadvantage: the flowerhead of smooth hydrangea is very large and attaches to the annual branch, which is top-heavy, so support is required. Therefore, several main branches and primary side branches should be specially trained during pruning to prevent lodging during blooming.