This is the fastest way for succulent plants to be killed. 5. If the potting material isn't suitable for succulents and cactus plants it is best to avoid using store-bought soil. Excessive moisture in the terrarium can cause mold in cactus. This can be avoided by not allowing water to pool and by maintaining good airflow. This means that most of the leaves are still healthy enough to grow into plants. Succulents are more resilient than other plants, as noted. They are exactly what you think - they put out more energy and light! It is easy to rush off to do research.