Succulents are a diverse group of plants adapted to arid or semi-arid climates, primarily through their ability to store water in fleshy leaves, stems, or roots. This water-storage capacity allows them to thrive in dry conditions but is also their greatest vulnerability when temperatures drop below freezing. Whether they can survive frost depends heavily on the specific plant species and the severity and duration of the cold event.
Understanding Succulent Vulnerability to Freezing
The fundamental reason succulents are damaged by freezing is related to their high internal water content, which can be over 90% in some tissues. When the surrounding air temperature falls to 32°F (0°C) or below, the water within the plant’s cells begins to freeze. This freezing process causes water to expand and form sharp ice crystals.
The physical expansion of these ice crystals exerts pressure on the plant’s delicate cell walls. This pressure ultimately causes the cell walls to rupture, a process that is irreversible and leads to the collapse of the tissue. Damage often appears as mushy, blackened, or translucent areas on the leaves and stems.
Some cold-hardy varieties produce natural cryoprotectants, such as sugars and solutes. These compounds act as a natural antifreeze, lowering the freezing point of the cellular fluids to offer a degree of protection.
Hardiness Based on Succulent Type
Succulents can be broadly categorized into groups based on their natural tolerance for cold. Tender, or “soft,” succulents, which include popular varieties like Echeveria, Crassula (Jade), and Kalanchoe, are highly susceptible to damage. These plants generally cannot tolerate temperatures below 32°F (0°C). Many may show signs of stress, such as discoloration, when temperatures consistently drop below 40°F (4°C).
A second category includes semi-hardy types, such as some Aloes and certain tender Sedum species. These can endure brief dips slightly below the freezing point, often into the mid-20°F range (about -4°C). However, prolonged exposure to these temperatures will cause significant damage.
The most resilient group is the cold-hardy succulents. These are native to mountainous or temperate regions and have evolved to survive extended periods of freezing temperatures, often far below 0°F (-18°C).
These resilient plants include Sempervivum (Hens and Chicks) and many ground-covering Sedum varieties. They can withstand harsh winter conditions, sometimes surviving under a blanket of snow, by entering a state of dormancy. This process slows their metabolism and conserves energy until spring. For example, many Sempervivum and some Opuntia (Prickly Pear) varieties are hardy down to USDA Zone 5, corresponding to temperatures between -20°F and -10°F (-29°C to -23°C).
Protecting Succulents from Cold
Preventative action is the most effective way to ensure the survival of vulnerable succulents when frost is forecast. For plants grown in containers, the simplest method is to move them to a protected location, such as a garage, covered porch, or indoors, before temperatures reach freezing. Potted plants are especially vulnerable because their roots lack the insulation provided by the ground.
For succulents planted directly in the ground, physical covers provide a necessary thermal barrier. Lightweight frost cloth, burlap, or old sheets should be draped over the plants before nightfall, ensuring the material extends to the ground to trap warmer air. The covering material should not directly touch the foliage, as this can transfer cold and cause damage.
The microclimate where a plant is situated can also offer natural protection. Planting succulents near a south-facing wall or under the eaves of a house provides a slightly warmer environment that shields them from direct frost exposure and cold winds. Reducing water in the weeks leading up to a frost event is beneficial, as dry soil holds heat better than wet soil, and a drier plant has less internal water to freeze.
Assessing and Treating Frost Damage
The signs of frost damage become apparent quickly, usually appearing as water-soaked spots, a translucent or “cooked” look, or a mushy, black rot on the leaves and stems. This appearance signals that the internal cell structure has been destroyed. Severely damaged succulents, where the entire core is mushy, are often beyond saving.
The most important step in treating a frost-damaged succulent is patience; wait until the threat of subsequent frost has completely passed before pruning. Removing the damaged tissue too early exposes healthy, tender parts of the plant to further cold damage. Once the weather has stabilized, use a sharp, sterilized knife or scissors to cut away all soft, blackened tissue. Ensure the tools are wiped with alcohol between cuts to prevent the spread of decay or pathogens.
If the damage is confined to the leaves and the central stem remains firm and green, the plant may still recover and send out new growth from the base or the undamaged stem. Even if the main plant is lost, gardeners should inspect the soil. Sometimes the offsets or the root system may have been insulated enough to survive and will sprout new growth in the spring.