How to prune spiraea thunbergii 'ogon'

Immediately after flowering, late spring to early summer. Shorten flowered stems by up to one-third, cutting to strong laterals. Remove one or two of the oldest, thickest stems entirely at the base each year to maintain an open, graceful habit.

Annually after flowering. Ogon spiraea blooms on old wood in early spring, so prune directly after flowering ends. Cut back flowered stems by one-third and remove the oldest, woodiest stems at the base to encourage arching new growth. Avoid hard autumn pruning — it removes the flower buds that form on the previous season's growth.

Shorten flowered stems by up to one-third, cutting to strong laterals. Remove one or two of the oldest, thickest stems entirely at the base each year to maintain an open, graceful habit.