Like most flowering plants, pruning hydrangeas can help the plants stay healthy and produce more blooms. Hydrangeas that are pruned incorrectly, however, may produce fewer flowers. What is important is not so much how hydrangeas are pruned but when they are pruned. There are three main types of hydrangeas, and while two of the types can be pruned at any time, the third type should only be pruned during a specific time of the year. Care should be taken when pruning not to spread disease or encourage pests.
One of the best tips for pruning hydrangeas is to understand that some hydrangeas flower on old wood, while others flower on new growth. Old wood is the previous year’s growth. This flowering pattern determines the timing for pruning. The various species of hydrangeas that bloom on old wood are especially vulnerable to improper pruning.
Oak leaf hydrangeas, or Hydrangea quercifolia, bloom on old wood. The various Hydrangea macrophylla species, such as mopheads, lacecaps, and big leaf, also bloom on old wood. Most H. quercifolia and H. macrophylla have white flowers. These plants should be pruned only during the summer, prior to August, to avoid removing buds that have set. Up to one third of the plant can be pruned away each year.
Hydrangea paniculata and Hydrangea arborescens flower on new growth. Pee Gee and Annabelle are examples of these species. These hydrangeas are often blue or pink and rarely require pruning. Hydrangeas that flower on new growth can be pruned at any time, including immediately after flowering. New, healthy growth can be encouraged by cutting the entire plant back to four inches (10 cm) tall.
Climbing hydrangeas do not need pruning to maintain healthy growth. They may need occasional trimming to keep them under control or to keep them contained. These hydrangeas, like H. paniculata and H. arborescens, can be pruned at any time. Pruning hydrangeas that bloom on new wood is sometimes done to encourage new growth. The new growth then supports the development of new flowers.
When pruning hydrangeas, the pruning shears should be clean and sharp. Dead or diseased wood should be removed as soon as it is seen, regardless of the time of year. The pruning shears should be cleaned with alcohol between cuts when cutting branches to avoid the spread of disease. Healthy branches are pruned by cutting just above a node. Pruned branches and clippings should be removed from the area as plant debris may encourage destructive pests.
