From our perspective as Crassula plants, temperature is a primary regulator of our metabolic processes. We are most comfortable and grow most vigorously in temperatures that mimic our native South African habitats. The ideal range for us is between 60°F and 75°F (15°C and 24°C) during the day. This temperate zone provides the perfect amount of thermal energy for photosynthesis, nutrient uptake, and cellular growth without causing undue stress. We appreciate a slight drop in temperature at night, ideally between 50°F and 55°F (10°C and 13°C). This daily fluctuation of 10-15 degrees is not just appreciated; it is crucial. It signals to us that it is time to respire and helps to intensify the colors on our leaves, promoting overall robust health.
We have a distinct growth cycle that is heavily influenced by temperature. In the spring and summer, we are in our active growth phase and can tolerate the warmer end of our ideal range. However, sustained heat above 85°F (29°C) can be problematic. It forces us to close our stomata to conserve water, which subsequently halts photosynthesis and can lead to sunburn on our leaves. Conversely, the winter months are our dormant period. During this time, we require a cooler rest. Temperatures between 45°F and 55°F (7°C and 13°C) are perfect. It is vital to keep us away from cold drafts and windows where temperatures might drop below 40°F (4°C), as this can cause severe cell damage and lead to our demise.
When it comes to atmospheric moisture, our succulent nature tells the story. We have evolved thick, fleshy leaves to store water, meaning we are adapted to arid, low-humidity environments. We prefer a relative humidity level between 30% and 50%. This is typically the natural humidity level found in most climate-controlled homes. High humidity is our adversary. When the air is constantly moist, our transpiration rate slows down, and the soil medium remains wet for dangerously long periods. This creates the perfect environment for fungal pathogens like powdery mildew and the dreaded root rot, which attacks our foundation and is often fatal.
These two factors do not act upon us in isolation; they are intrinsically linked. Warm air has a greater capacity to hold moisture than cold air. Therefore, a warm, humid environment is a significant threat, as it simultaneously encourages fungal growth and hinders our ability to cool ourselves through transpiration. Conversely, a very hot and extremely dry environment will cause us to lose water too rapidly, leading to desiccation and shriveled leaves. The sweet spot is a cool-to-moderate temperature paired with low-to-moderate humidity. This combination allows for efficient gas exchange, controlled water usage, and prevents the proliferation of diseases, creating a stable and comfortable home for us to thrive in.
