Agapanthus, or Lily-of-the-Nile, has been treasured by gardeners for literally centuries, and when you see 'Storm Cloud' in bloom, you'll understand why. This variety is at the larger end of the scale with its strap leaves forming mounds up to two feet tall and two to three feet wide. Sturdy flower stalks grow even taller, reaching three to four feet in height, with clusters of up to 100 violet blue flowers each. Though semi-evergreen here in the Pacific NW, any foliage that lingers may take on red to purple hues during the cold months.