Tender salvias and winter strategy

The most spectacular salvias — the ones with midnight flowers, hummingbird-magnet blooms, six-month flowering seasons — are tender. Salvia patens, with its gentian-blue open flowers, dies at the first frost. Salvia guaranitica 'Black and Blue' and its compact form 'Blue Enigma' will reach 150 cm by September and flower until November, but a night at -2°C kills the top growth and often the roots as well. Salvia 'Amistad', with near-black bracts and violet flowers, is borderline to -3°C in a very sheltered spot but usually succumbs. These are not plants you can leave outside in a British winter.

Your options are threefold. First, treat them as annuals — buy or grow from seed each spring, plant out after the last frost, enjoy them until October, then compost them. This works but wastes their potential for structure and maturity. Second, lift the roots in October, pot them up, and store them barely moist in a frost-free shed or garage at 5–10°C through winter. They will look dead but often resprout from the base in March. Water once a month just to keep roots alive. Third, take cuttings in late August and overwinter the young plants on a windowsill or in a cold frame. This is the method that feels most like propagation rather than rescue.

Salvia discolor, the Andean sage with near-black flowers and silver-white stems, is worth special mention. It is root-hardy to about -5°C if deeply mulched, but the top growth is always lost. More often, gardeners lift the tuberous roots in October, store them dry in barely-damp compost like dahlias, and replant in April. The same approach works for Salvia patens — the roots are swollen and dahlia-like. Treat them exactly as you would a dahlia tuber: lift after the first frost blackens the foliage, dry for a week, store in dry compost in a frost-free place, replant when soil warms to 12°C in spring.