indoors is never going to match what salvia will do outdoors. I am in zone 8 and my plants go outside for 7-8 months of the year..they grow insane ammounts in that time. When I bring them in I dont pay much attention to them I just make sure they get water..they slow down for sure durring that time but they do fine.
So, for people growing indoors I would suggest try growing them outdoors for the summer unless you are in the arctic or something..they should thrive as long as you keep them in filtered sunlight and dont let them dry right out..
You can get them going well indoors too, but I find that nothing beats the way they will just thrive outside.
Been growing them this way for 5 years without any problems. I have more dry leaf than I know what to do with..
Long live the unwoke.