This big salvia is sometimes known as Mexican purple sage, and indeed it hails from Mexico. It has lavender-violet flowers in late autumn and early winter. It has a sprawling shape, with arching stems to 3 m, making a lovely hazy background display if there is plenty of room for it. It is similar in form to Salvia iodantha, and flowers around the same time. The flowers look pretty with sasanqua camellias, tall white tree daisy (Montanoa bipinnatifida) and pink or white tree dahlia (Dahlia imperialis), which are all the same height as the salvia! Nearby shrubs can help support this rather lax plant; otherwise it will need some sort of staking. It should be cut back almost to the ground in late winter and pruned by half once or twice in summer to control its size. It grows well in part-shade, with morning sun and afternoon shade. Heavy frost will burn the tips of the plant but it will recover in spring.
Postscript: Although I loved the flowers on this salvia, in the end I took it out and gave it to someone with a large country garden. I just didn't really have the space for it and it was smothering nearby plants. I will miss those lavender blooms in autumn and winter!