Plant in a well-prepared bed, lightly conditioned with well-rotted compost or manure. Keep cutting the old stems out to encourage repeat flowers through the summer. Once the flowering period is over, resist the temptation to cut back the faded flower-stems until early spring, as they provide interest in the winter months. Once established, lift and divide congested clumps in spring. Protect roots during the winter with a thick layer of organic mulch around the root zone.