To understand our hardiness, you must first understand our origin. We are not typical garden plants; we are living stones, sculpted by millennia of evolution in the harsh, arid landscapes of southern Africa. Our entire being is a masterpiece of water conservation. Our bodies are composed of two fused, succulent leaves that hold a vast reservoir of moisture to survive years of drought. Our growth cycle is perfectly synchronized with a climate of brief, unpredictable rainfall followed by long, dry periods. We are engineered for survival in conditions of high light, low humidity, and, most critically, minimal frost.
The single greatest threat to our survival outdoors is the combination of cold temperatures and moisture. While we can endure intense, dry heat, our succulent tissues are highly susceptible to freeze damage. When the water stored inside our leaves freezes, it expands, rupturing cell walls and causing irreversible rot. This is not a matter of us being "a little delicate"; it is a fundamental physiological incompatibility. Even a single night of a hard frost (temperatures dipping significantly below freezing) can be fatal. Furthermore, a cold, wet winter is a death sentence. Our roots, adapted to dry, gritty soil, will quickly succumb to rot if sitting in moisture-laden, cold earth.
The USDA Plant Hardiness Zone Map is based on the average annual extreme minimum winter temperature. For us, this is the most critical piece of data. We can only consider surviving outdoors year-round without protection in zones where frost is a rare occurrence or non-existent. This typically means USDA Zones 10b and above (35°F / 1.7°C and higher). In these zones, the risk of a hard freeze is minimal. Even in Zone 10a (30°F to 35°F / -1.1°C to 1.7°C), a sudden cold snap could be dangerous. If you live in Zone 9 or below, the winter temperatures are simply incompatible with our survival outdoors. The average low temperatures in these zones are far below our tolerance level.
Surviving in a permissible zone (10b+) is not guaranteed; it depends heavily on creating the right microclimate and soil conditions. We demand absolute perfection in drainage. Our outdoor home must be a raised bed or a steep slope filled with a mineral-based substrate—at least 80% inorganic material like coarse sand, pumice, or perlite. This ensures water flows through instantly, leaving our roots dry. Placement is also vital. We need a spot that receives several hours of direct sunlight but is protected from heavy rains, especially during our dormant periods in summer and winter. A covered patio, a rockery with an overhang, or the south-facing side of a building can provide this shelter.
If you reside in a marginal zone like 10a or even a warm part of 9b, a "half-hardy" approach is possible but requires vigilant intervention. We can live outdoors during the warm, dry months from late spring to early autumn. However, as soon as nighttime temperatures consistently threaten to drop near 40°F (4°C), we must be moved to a protected environment. This means being potted and brought indoors to a bright, cool windowsill or into an unheated greenhouse where conditions remain frost-free and dry until the warmth returns in spring. This method respects our need for seasonal change while protecting us from the lethal cold.
