Overwatering is the most common cause of succulent plant deaths. It could also lead to dead air plants. The plant can grow to two feet in height in warm and sunny climates. A south-facing or west facing window will likely require you to place your succulent at least a few feet from the window. However, String of Hearts can be kept directly in a north-facing, or east-facing, window. Lithops do not require a lot of fertilizer. However, you can give them a small amount every few months to make them stronger and healthier.