How to prune thunberg spirea

Immediately after flowering (typically March–April). Once flowers fade, remove up to one-third of the oldest, woodiest stems by cutting them to ground level. Lightly shape the remaining framework to maintain an arching, open habit. Do not do a hard overall cutback in spring — this removes the flower buds that formed on last year's wood.

Annually, immediately after flowering. Thunberg Spirea (Spiraea thunbergii) flowers in early spring on the previous year's wood — unlike summer-flowering spireas, it must be pruned immediately after flowering, not in spring, or you will remove the coming year's flower buds. Thin out up to one-third of the oldest stems at the base after bloom to renew the plant.

Once flowers fade, remove up to one-third of the oldest, woodiest stems by cutting them to ground level. Lightly shape the remaining framework to maintain an arching, open habit. Do not do a hard overall cutback in spring — this removes the flower buds that formed on last year's wood.