The best time to plant out salvias is from late May to early June, or as soon as possible after the risk of late spring frosts have passed. This gives the plants the maximum time to establish and get their roots down before winter. If you purchase the plants late in the season, they are best kept frost free and planted out the following spring.
Many Salvias are reasonably hardy if planted in a sheltered sunny position. The soil should not be over rich, and winter drainage must be good. It is advisable to take a few cuttings in late summer as insurance. If required the tender salvias can be lifted, potted and grown on under protection in a greenhouse or conservatory.
Salvias have few demands, but some are brittle and require support (Salvia ‘Caradonna’ in my experience) when planted out in an open or windy position. The frequent removal of old flower heads will promote lots more new flowers. Do not be tempted to trim back and tidy your established salvias until late spring, when the new growth has started and the risk of frosts has passed.