Hydrangeas are beautiful flowers that thrive in bright sunlight, in well-watered soil, and, happily, without intensive trimming. To know when the time has come to prune hydrangeas, it is important to be aware of the two different types of stems of hydrangea plants. Hydrangeas that grow on old wood, such as macrophylla and oakleaf, and hydrangeas that grow on new wood, such as Annabelle and paniculata hydrangeas, each have specific times during which trimming is most beneficial.
Stems considered old wood have been on the hydrangea since the summer before the current season. Macrophylla hydrangeas, which include mophead and lacecaps, are usually blue or pink. As suggested by their name, oakleaf hydrangeas are white with leaves resembling those of an oak tree. Old wood hydrangeas should only be pruned in the summer months, especially June and July. In the months of August, September, and October, old wood hydrangeas produce the buds that will bloom the following summer. Therefore, if old wood hydrangeas undergo trimming in the fall, winter, or spring, it is likely that their buds will be clipped and there will be fewer blooms in the summer. On a yearly basis in the summertime, dead stems should be removed from old wood hydrangeas.
On the other hand, new wood stems develop on hydrangeas during the current season. Since new wood stems regenerate each year, these types of hydrangeas are less finicky when it comes to pruning. New wood hydrangea plants include Annabelle and paniculata types, both of which bloom white. Annabelle hydrangeas should not be pruned in the spring because this is when they prepare to bloom. As for paniculata hydrangeas, it is important not to prune them in the summer while they prepare to bloom. Paniculata hydrangeas also do not require pruning on a yearly basis, but only when branches cross.