Strictly speaking, it is a perennial, but it isn't a reliably long-lived one, for its roots quickly become woody and less productive with age. Best to treat it as a biennial - this summer's seedlings yielding next season's flowers - which is very easy as it seeds itself freely.
It makes a loose, gently sprawling plant with an easy-going, uncomplicated air, reaching 3ft to 4ft in height at flowering time. Its leaves are long, slender and tapered and they point skyward from the branching stems along their length. Early in the season, when growth is at its most vigorous, the whole plant appears to be trying to launch itself out of the soil.
Individually, the flowers are quite small - four rounded petals in the shape of a cross - but they are its glory. They are held in loose clusters, something like a phlox, on stems that sway on every breeze. They vary in colour from white to deep lilac - if you leave all the seedlings that sprout, you will have all the colours. In partial shade or at dusk the white flowers are magical. They take on a luminous quality, as if dimly lit from within. The close of the day also triggers the release of the delicious scent that has given the plant its common name of Sweet rocket or Dame's violet.
Flowering in spring and early summer, mine began on the May Day weekend this year, presumably encouraged by the season's early warmth (and a Labour win?). So partial am I to this plant that I enjoy it in just about any combination. Particularly effective would be the impressive, 7ft-high mullein, Verbascum olympicum, which would rise through the Sweet rocket to flower later on. With it, the summer-flowering bulb Allium "Globemaster" would produce football-sized starbursts of violet blooms on 4ft-high stems.
Three plants that look good together:
Allium 'Globemaster'Reuse content