Succulents are drought-tolerant plants characterized by thick, fleshy structures designed to store water. Because of this high water content, their tolerance for cold temperatures varies widely, making it impossible to assign a single survival limit. The specific temperature a succulent can endure depends entirely on its species, its geographic origin, its state of acclimation, and the duration of the cold exposure.
The Critical Temperature Divide
Succulent varieties are generally categorized into two groups based on their ability to withstand freezing temperatures. The vast majority of common houseplants, such as Echeveria, Crassula (Jade plant), and most cacti, are considered tender succulents. These plants originate from warmer, arid climates and are highly susceptible to damage when temperatures drop near freezing.
For these tender varieties, the critical threshold for concern is typically between 35°F and 40°F (1.7°C to 4.4°C), where growth can stop and discoloration may begin. Once the temperature drops to 32°F (0°C) or below, the plant faces a high risk of irreversible cellular damage.
In contrast, a select group known as hardy succulents, including many Sempervivum (Hens-and-Chicks) and certain Sedum (Stonecrop) species, can survive sub-freezing temperatures. These plants have evolved in mountainous or alpine regions and enter a state of cold dormancy. If kept relatively dry and properly acclimated, some exceptional cultivars of Sempervivum and Opuntia (Prickly Pear) can endure deep freezes, sometimes surviving temperatures as low as -20°F to -30°F (-29°C to -34°C).
How Cold Temperatures Damage Succulent Cells
The high water content makes succulents extremely vulnerable to freezing. When the temperature within the plant tissue drops below 32°F (0°C), the water molecules begin to turn into ice crystals. This ice formation does not just occur inside the cells, but often starts in the spaces between the cells, known as the apoplast.
As ice forms in the apoplast, it draws water out of the adjacent cells, a process called extracellular freezing. This leads to severe dehydration of the plant cells, similar to a physiological drought. If the temperature drops rapidly or low enough, ice can form directly inside the cells, and the expansion of this ice ruptures the delicate cell walls and membranes.
This mechanical damage prevents the cells from functioning, and upon thawing, the damaged tissue collapses. The result is the characteristic translucent, water-soaked appearance that quickly turns to black or brown mush, a clear sign that the cell structure has been fatally compromised and cannot recover.
Practical Strategies for Cold Protection
Protecting succulents from cold involves proactive measures focused on reducing internal water content and providing a thermal buffer. Modifying the watering schedule is an initial step; reducing irrigation in the fall lowers the water stored in the leaves and stems. A plant with lower tissue hydration is slightly more resilient to a short, mild freeze, though this does not make tender varieties frost-proof.
The most effective strategy for tender potted succulents is simple relocation. These plants should be moved indoors, into a garage, or beneath a covered patio before the first predicted frost. Even moving containers directly against a warm, south-facing wall of a house can provide a few degrees of beneficial radiant heat.
For plants remaining outside, temporary covers offer protection. Using a frost cloth, burlap, or a lightweight blanket draped over the plants can trap ground heat, elevating the temperature by a few degrees. Remove these covers during the day to allow for air circulation and sun exposure, preventing humidity and overheating.
Strategic placement can also utilize natural microclimates in the garden. Plants situated under roof eaves or near large stone or brick structures benefit from minimized exposure to cold skies and residual heat radiated by the materials. These small environmental variations can be enough to prevent damage during a marginal frost event.
Recognizing and Treating Freeze Injury
Freeze injury in succulents manifests through distinct visual cues that signify cellular collapse. Immediately after a freeze, affected leaves and stems may appear translucent, bleached, or water-soaked, quickly progressing to a soft, black, or brown mush. This is a definitive indication that the plant tissue has died.
When damage is noticed, it is important to resist the urge to immediately trim away the injured parts. The damaged tissue, though dead, can serve as a protective layer, shielding healthy tissue from further cold exposure. Pruning immediately after a freeze can expose vulnerable, healthy parts of the plant to subsequent cold snaps or introduce entry points for pathogens.
The appropriate time for treatment is after the threat of frost has completely passed and the plant has begun to show signs of new growth. At this point, use a sterile, sharp tool to carefully cut away all the mushy, blackened, or visibly collapsed portions of the plant. If the central stem or crown remains firm and green underneath the damaged leaves, the succulent has a chance to recover and sprout new growth as the weather warms.