by P. Bieneman
The showy blooms of the genus Hydrangea are hard to beat for reliable color in the garden, but when do you trim? We get this question a lot! There are basically old wood bloomers (bloom on last year’s wood) and new wood bloomers (bloom on wood produced this season). For the old wood bloomers, I would only prune to control size or shape. Also don’t forget to remove spent flowers from your plants. This will keep them tidy looking.
Old wood bloomers:
Hydrangea macrophylla– the traditional hydrangea such as the cultivar ‘Nikko Blue’. Blooms blue in acidic soil, pink blooms in alkaline soil, grows 3-5 feet tall and wide, and tolerates part shade. Trim in summer about 2 weeks after blooming.
Hydrangea macrophylla ‘Endless Summer’– a new macrophylla that blooms on old and new wood to assure successive color all season. Very hardy and mildew resistant. Colors range from pink to blue depending on soil pH. Grows 3-5 feet tall and wide. Prune after flowering in mid-summer. This is a remontant type so it could be pruned in spring and still bloom.
Hydrangea anomala petiolaris (Climbing Hydrangea)– a vigorous climber in shade to part shade. Attractive, glossy foliage that adheres itself to mortar or a strong wooden trellis. Blooms white, May through June. Can reach 20 feet, although trimming will contain growth. Prune after flowering in mid to late spring.
Hydrangea quercifolia (Oakleaf Hydrangea)– known for its interesting, oak leaf shaped foliage that turns bronze in the fall. Elongated creamy blooms in summer. Reaches 6-7 feet tall and wide. Tolerates dry conditions. Popular varieties include ‘Snow Queen’ and ‘Ruby Slippers’. Prune by mid-summer, no later than August.
New wood bloomers:
Hydrangea paniculata– unique, elongated chartreuse to white blooms in summer change to pink in the fall, regardless of soil pH. Grows 3-6 feet tall and wide. Site in sun or part shade. Can be trimmed in late winter/early spring to control size and flower production.
Hydrangea arborescens ‘Annabelle’– sports large white “snowball” blooms in June and July. Grows 3-5 feet tall and wide. Late winter/early spring pruning is recommended.