Sweet rocket, Hesperis matronalis, is a pretty biennial, bearing white or purple flowers similar to honesty. A packet of sweet rocket seeds is likely to produce flowers varying in colour from deep rich purple, through all the paler lilac shades to white – leave them to seed themselves and they will maintain this diversity indefinitely, gradually naturalising over a large area.The flowers’ fragrance is as sweet as a violet’s, and most pronounced in the evening. It looks good when allowed to drift, naturally through an informal sunny or partially shaded border, especially in a cottage garden or wildlife garden scheme.