This tough rockery plant bears sprays of violet starry flowers in spring and summer.

Although it is considered winter hardy, many growers bring it indoors and keep it in slightly moist soil on a windowsill, or in the basement under a lamp.

[citation needed] It is common to cut the plant down during the fall, so it can conserve energy during the winter, and then replant it in spring.

[2] Numerous varieties and cultivars have been developed for garden use, including 'Blue Gown', 'Blue Waterfall', 'Freya', 'E.H.

The cultivar 'Stella' has gained the Royal Horticultural Society's Award of Garden Merit.