Succulents are defined by their ability to store water in their leaves, stems, or roots, making them notably drought-resistant. This adaptation allows them to thrive in arid and semi-arid regions. While known for hardiness, their survival and active growth are directly tied to temperature control. Temperature acts as a primary signal, determining when a succulent grows, rests, and ultimately, whether it survives.
Maintaining the Ideal Temperature Range
Most succulent species, especially those commonly grown indoors, prefer an optimal temperature range for active, healthy growth. This zone typically falls between 65°F and 80°F (18°C and 27°C) during the day. Maintaining temperatures within this band allows the plant’s metabolic processes to function efficiently, promoting new leaf and root development.
Mimicking their natural environment requires a natural temperature fluctuation. Many succulents originate from deserts and mountains where the temperature drops significantly after sunset. Providing a drop of 10 to 15 degrees Fahrenheit at night is highly beneficial for the plant’s health.
This nightly cooling encourages the plant to utilize Crassulacean Acid Metabolism (CAM). The plant opens its stomata to take in carbon dioxide only at night when temperatures are lower. This minimizes water loss through transpiration, a crucial process that may halt if the nighttime temperature remains too high.
Understanding Cold Hardiness and Freezing Risk
The lower limit of a succulent’s temperature tolerance is often the most significant threat to its survival. Most non-hardy varieties begin to slow growth or enter a cold-induced dormancy when temperatures drop below 50°F (10°C). At this point, the plant conserves energy and requires significantly less water.
The absolute danger threshold for most popular succulents, such as Echeveria and Crassula, is the freezing point of water at 32°F (0°C). Succulents store a large volume of water in their fleshy tissues. When this water freezes, it expands, causing the plant’s cell walls to rupture. This results in irreversible tissue damage that appears as soft, mushy, and often blackened patches on the leaves.
The ability to withstand cold is species-dependent, leading to the distinction between “soft” and “hardy” succulents. Soft succulents, like Aloe and Kalanchoe, must be protected from frost and freezing temperatures. Conversely, hardy succulents, such as many Sedum and Sempervivum varieties, tolerate temperatures well below freezing by undergoing a deep dormancy.
If an unexpected cold snap is forecast, outdoor growers must take immediate action. Moving potted plants to a sheltered location, like a garage or porch, is the most effective method. For in-ground plantings, covering the plants with frost cloth or a thick blanket can trap ground heat, providing insulation above the ambient air temperature.
Dealing with High Heat and Heat Stress
Sustained temperatures above 90°F (32°C) pose a significant challenge, often causing a state called summer dormancy. During this period, the succulent stops active growth to conserve moisture and energy. Watering a plant during this dormancy phase can be detrimental, as the roots are not actively absorbing moisture, increasing the risk of rot.
High heat combined with intense, direct sun exposure is particularly damaging, leading to sun scald or sunburn. This damage appears as bleached, brown, or scorched spots on the leaves, which are permanently disfigured. The plant’s ability to photosynthesize is reduced in the affected areas.
To mitigate heat stress, repositioning the plant to receive some afternoon shade is often necessary during the peak summer months. Increasing air circulation around the plant, either by providing space between containers or using a fan indoors, helps to cool the leaf surface. In extreme heat environments, using a shade cloth can reduce the intensity of the sun’s rays without diminishing the necessary light levels.