“Hens and chicks” is the common name for the rugged, low-growing succulent groundcover belonging primarily to the genus Sempervivum. These plants are native to the mountainous regions of Europe and North Africa, where they have adapted to thrive in harsh, rocky environments. Unlike most succulents that require protection from frost, these rosettes are highly cold-hardy and are designed to survive freezing conditions. They can survive winter, provided specific steps are taken to manage moisture and prepare them for their dormant cycle.
Fall Preparation for Dormancy
Fall preparation focuses on initiating a necessary period of rest. As daylight hours shorten and temperatures drop in late summer and early fall, the plants naturally slow their growth to enter dormancy. This transition requires managing water and nutrients.
It is necessary to significantly reduce or completely cease watering in the early fall. The greatest threat to Sempervivum in winter is not the cold, but the combination of freezing temperatures and excessive moisture around the roots. Waterlogged soil will freeze and expand, destroying the root system through rot and ice damage.
All fertilization should be stopped completely by late summer. Applying fertilizer encourages tender new growth, which is highly susceptible to freezing damage and prevents the plant from properly hardening off for the winter. By withholding both water and nutrients, the rosettes compact their structures and concentrate internal sugars, which acts as a natural antifreeze.
Understanding Inherent Cold Tolerance
The remarkable winter survival of hens and chicks stems from their evolutionary adaptation to alpine climates. Most varieties of Sempervivum are reliably hardy down to USDA Zone 4, and some tolerate temperatures as low as -30°F (-34°C) in Zone 3. This cold tolerance is possible because the plant enters a deep state of dormancy where all metabolic processes slow to a near standstill.
The dense, layered rosette structure is a key biological adaptation that helps the plant survive. This compact form minimizes the surface area exposed to drying winds and severe cold, effectively protecting the growing point at the center of the plant.
These succulents possess a mechanism known as freezing tolerance, where the cells control the formation of ice crystals outside their membranes. This process prevents the crystals from rupturing the cell walls, allowing the plant tissue to survive being frozen solid. The ability to endure deep freezes, often for months, makes them a permanent feature in cold-climate rock gardens.
Practical Winter Management
Practical winter management focuses on protecting the plants from excess water. For plants established directly in the ground, the primary concern is proper drainage; if the soil is gritty and well-draining, little intervention is necessary. Snow cover is beneficial for in-ground plants, acting as a blanket of insulation that keeps the soil temperature stable and prevents damaging freeze-thaw cycles.
The most dangerous conditions occur during prolonged periods of winter rain or constant thawing and refreezing. Ensuring that no standing water collects around the base of the rosettes is crucial. Avoid placing organic mulch directly over the plants, as this can trap moisture and cause the rosettes to rot.
Container-grown hens and chicks require a different strategy because the soil mass in a pot freezes much faster and more completely than the ground. It is best to move containers to a sheltered, unheated space, such as a cold frame, porch, or unheated garage, where they are protected from rain and snow. The goal is not to keep them warm, but to keep them dry and shielded from rapid temperature fluctuations.
If containers must remain outside, they should be placed against a south-facing wall and elevated slightly off the cold ground to improve air circulation and drainage. Containers made of terracotta or clay are preferable to plastic, as the porous material allows excess moisture to evaporate, mitigating the risk of root rot during the dormant period. Once the plants are moved to their sheltered location, no watering is required until the start of the spring growing season.