Dame's Rocket begins blooming in mid-May, lasting for about four weeks.  It really brightens up the spring garden, and can be seen from some distance.  It is a biennial, but has been known to live more than two years where it is happy.  It is important to let it reseed itself.  It does best in shady areas, but can be grown in full sun if kept well-watered.  At night, the flowers give off an unforgettable scent.  I can't tell you what it smells like, because I forgot!  Mine grow 3'-4' tall.