Salvia divinorum, Diviners Sage Is Dying

I recently purchased several Salvia divinorum plants from you and they were in fine shape when I recieved them but I must be doing something wrong, because I have lost 4 of them and hope to save the remaining two. Problem is that the leaves are turning black on their tips and dropping off until they die. I have been watering but trying not to water too much and have used "Miracle Grow" liquid plant feed. Please tell me where I'm screwing up so I can save the last two.

This plant is sensitive to over-fertilization so make sure to use a very weak fertilizer solution and flush with rain water between fertilizer applications. If your water contains too many solutes, then you have to grow wetter or use rain water. I would suggest the latter in any case- if possible.
The plant likes it warm, but does not need as much light as most other sages.