Succulents store water in their leaves, stems, or roots, allowing them to survive in arid conditions. While often associated with desert heat, some varieties can survive winter outdoors, depending on the specific species and the local climate. Understanding the difference between frost-tender and cold-hardy types is the first step toward successfully growing them year-round.
Factors Determining Winter Survival
The primary factor determining a succulent’s outdoor winter survival is the local climate, categorized by the United States Department of Agriculture (USDA) Hardiness Zone system. This system maps regions based on the average annual minimum winter temperature, providing a baseline for plant survival. A plant’s listed hardiness zone must match or be lower than the gardener’s zone for it to survive the deepest cold.
The biological mechanism that allows some succulents to tolerate freezing is called cold-hardening or dormancy. In preparation for winter, these plants decrease the water stored in their cells, which prevents expansion and rupture when water freezes. Some hardy varieties produce cryoprotectant compounds that function like internal antifreeze. However, this tolerance is typically for dry cold; deep, prolonged freezing combined with moisture will kill most non-hardy succulents.
Succulent Varieties Built for the Cold
A select group of succulents is cold-hardy, capable of surviving temperatures as low as -20°F to -30°F, placing them in USDA Zones 5 and even Zone 4. These plants are distinct from the tropical types that must be moved indoors. The two primary genera built for the cold are Sedum and Sempervivum.
Sedum, commonly known as Stonecrop, includes many ground-dwelling species that can withstand snow cover, which acts as an insulating blanket. Hardy Sedum varieties survive extreme cold by dying back to the ground in winter, returning with new growth in the spring. Sempervivum, or Hens and Chicks, are recognizable by their tight rosettes and are tough, capable of surviving in rocky crevices. These plants are often hardy to Zone 4 and retain their foliage throughout the winter, sometimes changing color as a defense mechanism against the cold.
Essential Winter Preparation and Care
For succulents that are borderline hardy or must remain outdoors, preparation is required to ensure survival. Ensuring excellent drainage is crucial, as the combination of cold and excessive moisture is far more lethal than cold alone. Waterlogged soil causes the roots to rot long before freezing temperatures kill the plant tissue.
Gardeners should significantly reduce or stop watering outdoor succulents in the late fall to encourage dormancy with low moisture content. Container plants can be moved to a protected area, such as against a south-facing wall or beneath an overhang, to shield them from rain and frost. If a hard frost is anticipated, plants can be covered with breathable materials like burlap or frost cloth to trap ground heat.
Identifying and Addressing Freeze Damage
When a succulent freezes, the water inside its cells expands, causing the cell walls to burst and the plant tissue to collapse. The visual signs of damage include leaves and stems appearing translucent, water-soaked, or mushy, often turning dark black or brown. This tissue is dead and will not recover.
After a freeze, resist the urge to immediately prune the damaged parts. The collapsed, dead foliage provides insulation to the healthy tissue underneath, protecting it from subsequent cold snaps. Gardeners should wait until the danger of frost has passed in the spring before using clean tools to trim away the damaged sections. If the roots or the main stem crown remain firm, the plant has a chance to regenerate new growth.