Borderline-hardy subshrubs

This tier contains the salvias that make you check the long-range forecast in November. Salvia microphylla and Salvia greggii are subshrubs from the mountains of Mexico and Texas — woody at the base, evergreen in mild winters, flowering from June until the first hard frost. In a London garden with a south-facing wall, they are effectively perennial. In exposed Derbyshire, they will die unless you protect them or take insurance cuttings in September.

The famous cultivar Salvia 'Hot Lips' — a microphylla hybrid with bicolour white-and-red flowers that shift with temperature — is borderline hardy to about -7°C if the drainage is sharp and the site is sheltered. Salvia uliginosa, the bog sage, is herbaceous rather than shrubby but equally marginal: it survives wet winters in Surrey but rots in heavy Midlands clay. The key variable is not just minimum temperature but also wet cold versus dry cold. A mulch of grit around the crown in November makes the difference.

If you want these plants to persist, site them at the base of a warm wall, in raised beds or gravel gardens where winter wet drains fast. In October, mound 10 cm of coarse bark or leaf mould over the crown. In March, pull the mulch back and assess: if there is green growth low on the stems, cut back to it. If everything is brown and crisp, the plant is dead. This is why you took cuttings.