Salvia patens

A ballgown in blue, Salvia patens has the biggest and truest of blue flowers of any in the family. Many salvias are stalwarts of late summer and autumn and quite a few contribute that elusive true-blue colour to the gardener's palate. But for a small garden you can't do better than this species, which grows about 30cm from a tuber that you can lift and bring out of the frost in cold areas. Collect the few seeds you find – it's easy to propagate. (Nikau Hill)