From the perspective of the plant itself, the vast majority of Protea species have a very low tolerance for frost and freezing temperatures. They are not equipped with the physiological hardiness of plants from temperate climates that experience cold winters. Their native habitats are primarily in South Africa and Australia, in regions characterized by Mediterranean climates with mild, wet winters and warm, dry summers. Frost is a rare or non-existent event in these ecosystems. Consequently, Protea plants have evolved without the need to develop robust internal defenses against ice formation within their tissues. Exposure to temperatures at or below freezing (0°C or 32°F) typically results in severe damage or death.
When a frost occurs, the water inside and between the plant's cells freezes. For hardy plants, adaptations like anti-freeze proteins or the ability to move water out of cells prevent fatal ice crystal formation. Proteas lack these sophisticated mechanisms. The formation of ice crystals inside the cells is a catastrophic event. These crystals have sharp edges that puncture and shred the delicate cell membranes, which are the command centers for all cellular activity. Once these membranes are ruptured, the cell's contents leak out, and the cell dies. This damage is visually apparent as blackened, mushy leaves and stems. The plant cannot recover from this extensive cellular destruction. Even if the damage seems superficial, the vascular tissues responsible for transporting water and nutrients are often compromised, leading to a gradual decline.
While the general rule is a lack of hardiness, it is important to note that there is some variation within the Proteaceae family. A few species originate from higher altitude regions where light frosts may occasionally occur. These species have developed a slightly higher degree of tolerance. For example, the Protea caffra (Common Sugar Bush) or Protea gaguedi (African White Sugarbush) are known to withstand brief dips to around -2°C (28°F) once fully established. However, "tolerate" here means survival, not thriving; such events may still cause tip damage. In contrast, popular species like Protea cynaroides (King Protea) and Protea neriifolia are even more sensitive, suffering damage at temperatures just above freezing. The age and health of the plant also play a role; a well-established, mature plant with a deep and healthy root system has a better chance of surviving a mild, brief frost than a young, newly planted, or stressed specimen.
For a Protea plant growing in a climate where unexpected frosts are a possibility, its survival depends heavily on external, human-assisted protection or favorable microclimates. The plant's best natural defense is its location. Planting on a slope promotes cold air drainage, preventing it from settling around the plant. Similarly, a position against a sun-facing wall can provide radiant heat that keeps temperatures a few critical degrees higher. When a frost is forecast, protective measures are essential. Covering the plant with a frost cloth or burlap can trap heat radiating from the ground, creating a protective pocket of warmer air. It is crucial that the covering does not touch the foliage and is removed during the day. A thick layer of mulch around the base helps to insulate the root zone, which is vital for the plant's ability to regenerate even if the top growth is damaged.
