Should you prune salvia after it has bloomed?

yes ,after the plant has begun to grow again and after any danger of frost has passed. The old stems, although unsightly, protect new growth. According to Global Garden.com, many gardeners recommend waiting to prune until you see new shoots emerging near the base of the plant.

Trim your salvia very low in the summer to encourage re-blooming. Wait until your salvia has enjoyed a burst of early summer blooms, then cut the long stalks back deeply, removing at least half of the plant. If you have a mass planting of salvia, the plants will be at different heights. Cut these at varying levels, but cut back at least 50 percent of the plant. The salvia will reward you by bouncing back quickly with renewed vigor and lots of blossoms.