To understand the ideal USDA zones for us, you must first understand our fundamental needs. We are tender perennials, originally from South Africa, which means we thrive in warm, temperate climates. Our roots, stems, and foliage are highly susceptible to cold damage. We can tolerate a very light frost, but anything more severe causes cell walls to rupture, leading to blackened, mushy tissue and ultimately death. For sustained, year-round outdoor growth, the soil temperature must never freeze, and the air temperature should ideally not dip below 40°F (4°C) for prolonged periods. Our sweet spot for vigorous growth and prolific blooming lies in daytime temperatures between 70°F and 85°F (21°C - 29°C).
Based on these physiological needs, the USDA Hardiness Zones that allow us to thrive outdoors year-round are Zones 9, 10, and 11. In these regions, the average annual minimum winter temperature ranges from 20°F to 40°F and above. This provides the consistent warmth our root systems require to survive the winter without dying back.
In Zone 9 (20°F to 30°F), we can typically survive with minimal protection. A hard freeze is still a threat, so a layer of mulch over our crown is often necessary to insulate us from unexpected temperature drops. In Zones 10 (30°F to 40°F) and 11 (above 40°F), we are in our absolute element. Here, we can grow and often bloom continuously throughout the year without any fear of cold damage, replicating the conditions of our native habitat.
Even within these ideal zones, our survival is not guaranteed by temperature alone. Two other factors are paramount: microclimate and soil drainage. A favorable microclimate, such as a south-facing spot protected by a wall or fence, can absorb heat during the day and radiate it back to us at night, creating a pocket that is effectively a full zone warmer than the surrounding area. This can make the difference between life and death in a Zone 9 winter.
Furthermore, our crown—the central growing point at the base of our leaves—is extremely prone to rot. Well-draining soil is non-negotiable. Soggy, cold soil in winter is a far greater killer than cold air alone. It suffocates our roots and promotes fungal diseases that quickly prove fatal. Planting us in raised beds or amending the soil heavily with sand, perlite, or compost is essential for ensuring excess water drains away from our roots immediately.
For gardeners in zones 8 and below, the outdoor ground freezes solid in winter, making year-round outdoor growth impossible for us. In these regions, we are treated as vibrant annuals or potted plants that must be brought indoors before the first frost. While we can put on a spectacular show from spring until fall, we lack the genetic hardiness to withstand a hard freeze. Our cellular structure cannot acclimate to such conditions, and attempting to leave us outdoors would result in our complete demise.
