Because I have a lot of them, I use a weed eater and whack off the top third. They are blooming again in a couple weeks.
I do give them a a shot of Miracle Grow after the whacking but I like Miracle Grow.
Otherwise if trimming individually, cut the stalk down to the next branching stems.

beez -- Would you suggest deadheading (I only have three plants) individual stems as they blow their color? Or, waiting until ALL of the stems on a plant are done and then deadhead them all at the same time? I don't mind doing it individually (I do that with other perennials), but didn't know if one way would produce more color than the other.

I would do whatever you have time to do. Certainly removing each flower as it has faded would look better but it's not necessary.

You will have constant bloom without a lull period like I do if you regularly tend to them.

bbeez -- Thanks! That's what I'll do then. I actually sort of enjoy the walk through the garden (it's not very large) and deadheading the perennials.

bbeez -- (Sorry, I've been out of town...just getting back and getting back to GW...) One more question: I deadheaded the salvia before I went out of town. When I came back, they were blooming again (good!), but the flower stalks were all sort of short and not as nice and tall as they were before (not good?). Is that normal and how do I get them to bloom on taller stalks again?

Fertilizer