Succulents are well-known for their drought tolerance, but their ability to survive cold weather varies significantly by species. Defined by their ability to store water in their leaves, stems, or roots, succulents are fundamentally vulnerable to freezing temperatures due to this high internal water content. Most tender varieties, commonly grown indoors or in mild climates, cannot survive freezing conditions. However, a specific group of hardy genera has evolved mechanisms to thrive even when temperatures drop below freezing.
Defining Succulent Cold Hardiness
The biological challenge for succulents in cold weather stems from the water stored within their cells. When the temperature falls to 32°F (0°C) or below, this water turns to ice, causing the crystals to expand and rupture the plant’s cell walls. This cellular damage is irreversible and results in the characteristic blackening and mushy texture seen in frost-damaged plants. For most species, such as Echeveria and Crassula, temperatures consistently below 40°F (4°C) induce cold stress, slowing metabolic processes. Vulnerability is compounded by moisture, as wet soil holds cold longer, increasing the risk of root rot and freezing damage.
Identifying Cold-Tolerant Varieties
Not all succulents originate from hot deserts; many alpine and mountainous varieties have developed true cold hardiness. These plants reduce their internal water content and increase solute concentration, acting as a natural antifreeze, allowing them to survive deep freezes. This true cold hardiness differs from those that are merely “frost-tolerant,” which handle only a brief, light frost.
The most reliable examples belong to the genera Sempervivum (Hens and Chicks) and many species of Sedum (Stonecrop). Sempervivum species are renowned for their resilience, with many capable of surviving temperatures as low as -30°F (USDA Hardiness Zone 4). Their defense involves closing their rosettes tightly and changing color, protecting the growing point during winter dormancy. Certain Sedum varieties, particularly creeping groundcover types, also exhibit impressive cold tolerance, sometimes surviving down to -40°F. These plants typically shed or dry out their foliage in winter, minimizing exposure and retreating to a dormant state that allows them to regrow from the crown in spring. Gardeners seeking year-round outdoor options should focus exclusively on these cold-hardy species, which are adapted to freezing temperatures and dry soil conditions.
Protection Strategies for Tender Succulents
Tender succulents, including Echeveria, Crassula, and Haworthia, must be actively protected when temperatures threaten to dip below 40°F. The simplest strategy for potted plants is to move them indoors before the first expected frost. Inside, place them near a south-facing window or under supplemental grow lights to ensure adequate light during winter. Reducing or stopping watering completely is also effective, as dry soil is less susceptible to freezing than wet soil.
Tender succulents remaining outdoors, such as those planted in the ground or those too large to move, require temporary physical protection. Covering plants with frost cloth or a breathable fabric, such as an old bedsheet, provides temperature protection by trapping radiant heat and preventing frost crystals from settling directly on the foliage. Plastic sheeting should be avoided, as it prevents the plant from breathing and can lead to damage from condensation. For greater protection against a hard freeze, some gardeners use incandescent Christmas lights strung beneath the fabric cover, which generate a small amount of heat. Protective coverings should be secured and removed during the day if temperatures rise significantly, preventing overheating or dampness.
Assessing and Treating Cold Damage
Cold damage often presents visually as translucent, blackened, or mushy areas on the leaves and stems. This appearance results from ruptured cells releasing their contents, signaling that the affected tissue is dead. Wait a few days after the freeze before beginning treatment, as the full extent of the damage may not be immediately visible.
The first step is to move the damaged plant to a protected, warmer area and carefully prune away all soft, dead material using clean shears. Removing the damaged tissue prevents rot and fungal infections from spreading. If the central stem or crown remains firm and green, the plant is salvageable and may push out new growth in the spring. After pruning, avoid watering or fertilizing, allowing the plant to heal and remain dry until the weather warms.