‘Darwin’s Blue’ is a clump-forming perennial that can reach a height of 16” with a 12” spread. It blooms in summer with dense terminal spikes of purple-blue flowers held above the dark green foliage. It prefers moderately fertile, constantly moist (not wet) soils in full sun. It will tolerate light shade. Deadhead to encourage additional bloom.  After bloom, it may be cut back to provide a tidy ground cover.