Salvia divinorum plants .. browning leaf edges?

Hi.
I'm quite worried so i'll make this quick.
The leafes edges on some of my salvia plants are turning brown.
One leafe I noticed.. it had brown edges and eventually it turned completly brown and then fell off the plant before it was very big.

I'm really worried because most of my precious plants have these brown leafs starting to develop.

I water them enough (the leaves are not drooping and they are the right color), and they seem the right amount of sunlight. Also I open the door to them so they get pleanty of CO2 (not at night though).

So I really would like to know the cause of this if anyone knows?
And if my plants are going to die from this or what..?

Thanks

 

try misting the leaves and go get some miracle-gro mix and use that on the leaves and when you water it. It may just be that the soil is toast. I don't know how demanding salvia is with that.

 

I mist them 2 - 4 times a day, and I fed them a couple of days ago on tomato food (it says on the back it's sutaible for all plants). They're in compost I got from a garden center for flowers.
On one of the plants it looks like it's completly going to die from it because all of the leaves are 60% brown...
Please help!

 

ok so..
update.
i was looking at the leaves of one of my plants today. just toutching them. and ALL OF THE LEAVES FELL OFF! apart from one.
these are tiny plants (about 6 inches high).
is this normal??
it looks really pathetic now there is just one browning leave on a stork now :/

 

i think it might be from humdity problems or root problems. one of my plants died because the roots were too packed with the soil from the original box it came in, and the roots weren't able to spread. also the soil was just miracle gro and saturated with water, and with no perlite or vermiculite....i ended up suffocating my own plant . all of the leaves started browning and no amount of misting or anything helped. browning edges are notorious on salvia though, it could be different reasons too.