The olive tree (Olea europaea), a species revered since ancient times for its fruit and oil, originated in the Mediterranean basin, a region defined by hot, dry summers and mild, wet winters. The tree was introduced to the United States centuries ago by Spanish missionaries in the American Southwest. Today, the olive tree is a symbol of the Mediterranean diet and has found pockets of suitable habitat across the US.
Essential Climate and Soil Conditions
Olive cultivation requires specific environmental conditions that mimic its Mediterranean heritage. The tree needs a period of winter chill, called vernalization, to develop flower buds, typically accumulating 250 to 300 hours between 32°F and 47°F. Without this cool period, fruit set will be significantly reduced or entirely absent.
While olives tolerate high summer heat, they are highly sensitive to hard freezes. Most commercial varieties thrive in USDA Hardiness Zones 8 through 10. Temperatures below 22°F can kill smaller branches, and sustained temperatures below 15°F can severely damage or kill the entire tree. Furthermore, the olive tree requires well-drained soil, as it is intolerant of standing water. Olives tolerate a broad pH range and grow in various soil types, often producing well in moderately alkaline conditions.
Established Commercial Growing Regions
The majority of commercial olive production in the US is concentrated in California, the state whose climate most closely mirrors the Mediterranean ideal. The Central Valley, particularly the San Joaquin Valley, serves as the heart of US olive oil production. This region offers the necessary combination of consistent winter chilling, long, hot, dry summers, and sufficient land for large-scale operations.
These established areas support both table olive production (e.g., Mission and Manzanillo) and high-density cultivation of oil varieties (e.g., Arbequina and Koroneiki). Beyond California, smaller commercial groves exist in specific regions that share similar climatic characteristics. This includes parts of West and South Texas, utilizing hot, arid conditions and cold-tolerant cultivars. Specific areas in Arizona, such as the Yuma region, also host successful operations, benefiting from the intense heat needed for oil accumulation and managing humidity.
Expanding and Marginal Growing Areas
Olive cultivation is progressively expanding into regions that face greater climatic hurdles but offer a suitable combination of factors for small-scale or specialized production. The Southeastern US, including parts of Florida, Georgia, and South Carolina, is an expanding area, particularly with highly cold-tolerant varieties. The primary challenge here is the high summer humidity, which increases the risk of fungal and bacterial diseases, a contrast to the dry-summer environment olives prefer.
In these marginal zones, the required winter chill hours are often met, but growers must contend with the potential for sudden, severe cold snaps and managing canopy diseases. The Pacific Northwest, notably the Willamette Valley in Oregon, is also a region of experimental growth. Here, the challenge is not only the occasional hard freeze but also the lack of sufficient growing degree days to fully ripen fruit before the onset of winter. Success in these areas is often limited to specific microclimates, such as protected slopes or coastal regions.
Selecting the Right Cultivar for US Zones
Choosing the correct cultivar is essential for success when planting olives outside of optimal zones. Traditional California varieties like Sevillano and Manzanillo are well-suited for the milder climates of USDA Zones 9 and 10, but require protection from severe winter cold. For colder, expanding zones, cold-tolerant varieties are necessary. The Spanish Arbequina is widely planted in Texas and the Southeast due to its high cold tolerance, withstanding temperatures down to approximately 15°F. Other cold-hardy oil varieties, such as Arbosana and Koroneiki, are favored for consistent production in Zone 8 environments.