Set 15 to 18 inches apart. Choose a location in full sun or light shade, where the soil is moderately fertile and – this is essential – well-drained.
Removing spent flower heads will prolong blooming period. An application of a balanced fertilizer in the spring, as growth commences, is a good idea. Plants may need dividing every 3 or 4 years, for renewal; do this in the spring or fall.