This probably should have been brought up back in the fall when lots of us were spending our free time raking fall leaves, but what the heck.
For those of us who live in zones where many salvia species are marginal at best or not hardy at all here is something you might want to try. In late fall when the ground begins to freeze you cut your salvias down to the ground and cover the crown with a bag or bags full of leaves - preferably black plastic bags. This does two things. It keeps water out of the crown and also prevents the ground from freezing. My own experiments indicate that you pick up roughly two zones. In other words a zone 6 garden is now able to preserve in-ground zone 8 plants.
This doesn't work well for all plants, woody plants like microphylla/greggii can be tricky, but for dieback perennials like guaranitica, Indigo Spires, and other herbaceous salvia it works very well.
