Hi guys! First of all, here see my bigger plant :
Now here see why im posting this topic :
The stem is turning darker and i think if i do nothing soon the whole plant will die. Maybe its because the plant is too big and i still use this tiny pot (its from yogurt ). Could you tell me why my plant is looking like that? It could also be from lack of vitamins, but i nourish it every other week.
P.S. Sorry for posting this here!

Ya know... diagnosing over the internet....

But I'd say this:
-More light
-Make sure those pots have drainage holes and the soil is drying out

I think you are right also about pot size, a much bigger pot with good drainage is required (the bigger the root system, the more prolific the growth of stems/leaves). Be careful about more light as Salvia does not tolerate too much direct sunlight.

What is that black wire for? It looks electrical in nature.