Grevillea, a diverse genus of evergreen shrubs and trees native to Australia, is prized for its unique, spider-like flowers and often fine, needle-like foliage. Its ability to survive winter is not a simple yes or no but is intrinsically linked to the specific USDA Hardiness Zone and the particular Grevillea species or cultivar in question.
From a plant's perspective, winter survival hinges on two primary threats: freezing temperatures and excess moisture. Grevilleas have evolved in well-drained, often sandy or rocky, Australian soils and are exceptionally drought-tolerant. Their roots are highly susceptible to fungal root rot in cold, waterlogged soil. A hard freeze (temperatures significantly below freezing) causes the water within plant cells to freeze, forming ice crystals that rupture cell walls, leading to tissue damage and die-back. Therefore, a plant's hardiness is a measure of its cellular tolerance to this freezing process.
Most commonly available Grevillea varieties are best suited to USDA zones 9 through 11. Within this range, their survival strategy relies on minimal frost exposure.
Zones 9b-11 (25°F and above): In these zones, many Grevilleas, such as the popular Grevillea rosmarinifolia (Rosemary Grevillea) and Grevillea juniperina, can survive winter outdoors with minimal protection. They experience only light, infrequent frosts, which may damage the most tender new growth but are unlikely to kill the woody stems and main root system.
Zones 8b-9a (15°F to 25°F): Survival becomes marginal. Hardier species like Grevillea victoriae (Royal Grevillea) or robust hybrids such as 'Canberra Gem' may persist but will require strategic placement. They must be planted in a very sheltered microclimate—against a warm, south-facing wall that radiates residual heat, for example—and in extremely well-draining, mounded soil to combat moisture.
Zones 8a and below (below 15°F): Prolonged exposure to these temperatures is generally fatal. The plant's cellular defenses are overwhelmed, resulting in severe die-back or complete death of the plant. In these zones, Grevillea is best grown in containers that can be moved to a protected, unheated location like a garage or greenhouse during the coldest months.
Not all Grevilleas possess the same cold tolerance. Their native origins dictate their strategy. Species from high-altitude, cooler regions in Australia, like Grevillea lanigera (Woolly Grevillea) from the mountains of New South Wales, have developed slightly better resistance to cold. Their adaptation may include smaller, tougher leaves or a low, dense growth habit that helps protect the crown of the plant from wind and radiated cold from the ground.
A plant's survival is not determined by air temperature alone. The soil condition is arguably more critical. Planting a Grevillea in heavy clay soil is a near-guarantee of failure in any zone with winter rain. Amending the soil heavily with gravel, pumice, sand, and compost to create a fast-draining environment is essential. Furthermore, a sunny, sheltered location that is protected from harsh, desiccating winds significantly reduces winter stress, preventing foliage burn and reducing the wind chill factor that can lower the temperature around the plant.
