 The species and its cultivars are not able to survive the harsh winters of northern or montane climates, being killed by temperatures below about .Younger wood is more floriferous, so even if frosts do not kill the previous year's growth, the shrub is usually hard-pruned in spring once frosts have finished, to encourage new growth.The removal of spent flower panicles may be undertaken to reduce the nuisance of self-seeding and encourage further flower production; this extends the flowering season which is otherwise limited to about six weeks, although the flowers of the second and third flushes are invariably smaller.