Grevillea, a genus within the Proteaceae family, is native to Australia. From a botanical perspective, this origin is crucial as it defines the plant's fundamental requirements. Most species have evolved to thrive in well-drained, often sandy or gritty, acidic to neutral soils. Their roots are particularly susceptible to fungal pathogens in heavy, water-retentive clay soils, especially in colder, wetter conditions. Furthermore, many Grevillea species exhibit proteoid roots—dense clusters of fine rootlets that are highly efficient at nutrient uptake in impoverished soils. This makes them extremely sensitive to high levels of phosphorus found in many general-purpose fertilizers, which can be toxic to them.
When selecting a variety for your US region, the plant's cold hardiness is the primary determinant. The USDA Plant Hardiness Zone Map provides the essential framework. However, a second critical, often overlooked factor is humidity and associated summer rainfall. Many Grevillea species are adapted to a Mediterranean climate with dry summers and wet winters, or arid conditions. High humidity, particularly when combined with summer thunderstorms, can create conditions conducive to root rot and fungal leaf diseases, which can be fatal even if the temperature is within the plant's tolerance.
For gardeners in California, Arizona, and similar climates (USDA Zones 9-11), the options are extensive. These regions mirror the plant's preferred conditions. Grevillea 'Noellii' is a robust, compact shrub tolerant of coastal conditions and light frosts. Grevillea rosmarinifolia (Rosemary Grevillea) is an excellent choice for its fine, needle-like foliage and prolific red flowers, thriving in hot, dry, and sunny locations. For a larger architectural statement, Grevillea 'Superb' is a vigorous hybrid offering large, intricate pink and cream flowers that are highly attractive to hummingbirds. All require excellent drainage and full sun.
For those in the Pacific Northwest, parts of the Mid-Atlantic, and other regions in Zones 7-9, selection must focus on cold tolerance and humidity resistance. Grevillea victoriae (Royal Grevillea) is one of the hardiest species, with some cultivars tolerating brief dips to 0°F (Zone 7). Its felted, gray-green foliage offers some resistance to damp air. The hybrid Grevillea 'Canberra Gem' is another top contender for cooler zones, valued for its toughness, spider-like red flowers, and ability to handle colder temperatures better than many others. Siting these plants in a south or west-facing location with maximum sun exposure and wind protection is vital for success.
For gardeners outside the recommended zones or with unsuitable soil, growing Grevillea in containers is a viable botanical workaround. This allows for perfect control over the soil medium—a must is a very porous, acidic mix, perhaps amended with sand, pumice, or bark chips. Container growth also enables the plant to be moved to a protected location, like a sunny garage or greenhouse, during periods of extreme cold or excessive winter wetness, effectively expanding its possible range. Dwarf varieties such as Grevillea lanigera 'Coastal Gem' or Grevillea juniperina 'Molonglo' are ideally suited for this purpose due to their compact growth habit.
