When a terrarium is overcrowded, the plants cannot grow to their full potential. Best practice is to repot the plants into new bigger containers. This terrarium was glass, so we had to use a hammer to break the glass and remove the plants!
Special soil for cacti and succulent plants (called Cactus Mix) is not too dense, so the water can drain out and the roots do not drown.
We carefully removed the glass bits that were stuck in the roots and soil before repotting.
Occasional Observations of Traveling Technology Coach 