Timing is important when pruning flowering shrubs. It can make the difference between a delightful show and a disappointment.
Buds of spring bloomers form on "old wood," which means they form during the late summer and autumn of the previous year. Therefor, the best time to prune spring bloomers is right after you enjoy the floral display, before the flower buds form on the new summer growth. If you prune them at any other time of year, such as early spring or fall, you sacrifice future blooms
Summer bloomers such as spirea and butterfly bush form buds on the current year's new growth. They should be pruned in late autumn or early spring before the new flower buds form.
Annabelle hydrangea (Hydrangea arborescence) and PeeGee hydrangea (H. paniculata) also bloom on the current year's growth but rarely need significant pruning.
The Endless Summer hydrangea flowers on both old and new wood. Old flowers should be pruned out sparingly to maximize new blooms.
Late summer or fall bloomers such as Rose-of-Sharon (Hibiscus syriacus) are best pruned in early summer. Pruning in late summer or early fall encourages new leafy growth that will not mature in time to harden before the first frost, which usually damages the tender new growth on shrubs pruned too late in the year.
