I only grow CA native salvias inside of CA and I don't fertilize at all. I do, however, add stones and mulch to their habitat for temp. and moisture conservation.

I grow all sorts of Salvias and find that giving the whole ground area around the Salvias I just finished pruning a good sprinkling of fertilizer is of benefit. I just use regular garden fertilizer. My gardens are too big to spread compost, but we do spread out the chopped Fall leaves as far as they will go. I use my precious compost when planting.