Hesperis White (Sweet Rocket)

The white sweet rocket, and the better of the two for an evening garden. Same branching stems at 75 to 90cm, same clusters of four-petalled flowers, same heavy violets-and-cloves fragrance released as the light goes. The difference is that the white flowers hold light at dusk while the purple ones disappear into the shadows.

That combination of a flower that glows and a scent that arrives at the same moment is why it is a fixture of moon gardens. It also fills an awkward gap. Tulips are finished, roses have not started, and there is very little white about in May and June. This covers it.

It is a biennial, so leaves in year one and flowers in year two, then it dies and reseeds. Grown near purple sweet rocket it will cross and the seedlings come back purple, so keep them apart if you want the white to hold.

It is the same orange tip butterfly food plant as the purple form, so leave a few seed pods standing. Like all brassicas it mildews in a dry late summer and looks tired afterwards.