Grown mainly for the foliage, 'Purple Knockout' has compact basal rosettes of shiny burgundy leaves that turn to deep purple in summer, then to red in the fall. Spikes of pale lilac-blue flowers appear in spring and summer, but sometimes the flowers have only calyces and no petals. We have not been able to determine the cause of this, but a cut back of the stems promotes new blooms that often have petals the second time around. Petals or no, the flowers are attractive to bees and butterflies. Very easy to grow in just about any soil, it will self sow to spread and become a dense groundcover that makes a great native substitute for Ajuga.