You may want to plant them in the ground if you have a suitable location. They can grow very fast in the ground, as much as two meters in six months. The stems of Salvia divinorum are not very strong, when the plant gets taller than about one meter tall it will fall over if not given support. Sometimes the stem will break off, but usually it will just bend over and if the bent over stem is in good contact with moist soil it will quickly root and eventually send up new stems from the new location. This is the main way that the plant spreads in the wild since it almost never produces viable seed.
Dry air tends to cause the plant to put out deformed growth.