hiya zuzu,
I've been collecting this genus for some time and have a very simple cultivation philosophy. Leave them the heck alone. Sages, like many members of the mint family find a spot they like via rooting stems or by just out competing anything around them. When they find the spot they like, it's very much a "Katie bar the door" kind of thing. I feed all of our species salvias once a year with a mix of blood, bone, alfalfa, kelp and cottonseed meal. A layer of compost from "Mount Manure" (a maggiemoo-ism) kept over the roots seems to keep them cool enough to thrive in an otherwise rather hostile environment. Sages do, in fact, eat a lot, however they seem to prefer a more gradual/continuous food supply that is well supplied using simple organic gardening methodologies.
I'm a huge fan of this genus and continue to hunt down the ones that are either endangered in habitat, or have been cloned for so many generations (nursery business) seed hasn't been seen since the beginning of the last century. We've been fortunate to donate seed from some of these threatened species to seed banks around the world in order to ensure that Sage-oholics will have some species to kick around well into the future.
I really do admire this cubit and how it is evolving,
don
