Spireas are deciduous, multistemmed shrubs that have been cultivated in the South since the mid-1800s.
When you prune a spirea depends on whether the flowers occur on last year’s growth or on current season’s shoots.
Spring-flowering spireas bloom on last year’s wood and should be pruned when their flowers fade. This will encourage new growth that will mature over the summer and fall and bear next year’s flowers.
Spring-blooming spireas include baby’s breath spirea, bridalwreath spirea, double Reeves spirea, and Vanhoutte spirea.
To prune them, first remove any dead or crossing branches. Then, thin out one-fifth to one-third of the oldest branches to the ground. Shorten long, lanky branches by cutting back to a side branch or bud oriented away from the center of the shrub. Finally, tip back a few of the branches to encourage branching from below the cut to create a full-looking display.
Spireas that bloom on current season’s growth should be pruned in late winter before budbreak. They include Billiard spirea, bumald spirea, and Japanese spirea and its cultivars and hybrids.
Thin out the oldest shoots at ground level to reduce overcrowding. Cut them back by two-thirds of their height or close to the ground to encourage the production of many young shoots that will bloom later in the season. To maintain an informal structural framework, stagger your pruning cuts.
During the growing season, removing the spent flower heads will promote continuous flowering, especially in Shibori Japanese spirea and bumald spirea.