Quick Guide: spring, hardy, semi-shade, height: 23cm/9in, width: 60cm/24in

Of the large number of species bearing the name, only one arabis, A. albida (syn. A. caucasica) is suitable for the rock garden. A perennial, it forms a cushion of grey-green, oval leaves covered in white flowers 1cm/ 1/2in wide from early spring to summer. The species is an invasive plant which cannot be allowed to range unchecked over the rock garden, but, in partnership with alyssum and aubrieta, can look wonderful scrambling over a dry wall or bank. Named varieties are recommended for the rock garden proper.

GROWING Plant in well-drained soil in autumn or spring. The stems can be pegged down for the sake of neatness; cut back hard after flowering to remove faded flower stems.

PROPAGATION Lift, divide and replant in autumn.

VARIETIES `Flore-Pleno', double, white; `Snowflake', large, single flowers, white; `Corfe Castle', deep magenta.

POSSIBLE PROBLEMS Gall midge larvae on young growth; white blister, club root.