The hazelnut (Corylus avellana) is a commercially important nut crop prized globally for its use in confectionery and as a snack. Successful commercial production of this deciduous tree depends entirely on meeting specific environmental needs, which dictates the limited geographical areas where it can thrive. Location selection is the most important factor for cultivation, as these requirements govern the tree’s dormancy cycle and vulnerability to disease.
Ideal Climatic Requirements
Hazelnuts require a distinctly temperate climate, characterized by cool winters and mild summers, for proper growth and nut development. A mandatory period of winter chilling is necessary to break dormancy. Most cultivars need 800 to 1,200 hours at 0°C to 7°C (32°F to 45°F) for optimal yields. Insufficient chill hours cause irregular bud break and sparse flowering, severely limiting production.
Temperature management during spring and summer is a major concern, particularly regarding frost events. While dormant trees are relatively hardy, late spring frosts can severely damage the male catkins and developing female flowers. Conversely, extreme summer heat causes stress, leaf scorch, and reduced productivity. Temperatures should ideally not exceed 30°C to 35°C (86°F to 95°F) for extended periods.
Moderate and consistent rainfall is preferred, with an annual requirement of 750 to 1,000 millimeters (30 to 40 inches). Trees are most sensitive to water stress during the nut-filling period in summer and early fall, often necessitating supplemental irrigation in drier regions. A dry period is important just before and during harvest, as wet ground complicates mechanized harvesting and increases nut moisture content.
Essential Soil and Site Conditions
The physical properties of the orchard site are as determinative as the climate, with soil drainage being the most important condition. Hazelnuts are extremely intolerant of “wet feet”; waterlogged soils quickly lead to root rot and tree death. Deep, well-drained loamy or sandy-loam soils are considered optimal for commercial cultivation.
The soil profile must be deep, ideally extending 1.5 to 3.0 meters, to accommodate the tree’s extensive, fibrous root system. A soil pH range between 6.0 and 7.5 is acceptable, but a slightly acidic to neutral pH of 6.0 to 6.5 is most suitable for nutrient availability. Heavy clay soils can be used only if drainage is excellent.
Site topography plays a role in mitigating temperature and drainage issues. Planting on gentle slopes is preferred, as it promotes water runoff and good air drainage, preventing the pooling of cold air that causes frost damage. Sites should also provide adequate sun exposure and protection from strong, drying winds that can damage young shoots.
Global Centers of Production
The world’s largest hazelnut-producing regions meet these climatic and soil requirements. Turkey, the dominant global producer, concentrates cultivation along the Black Sea coast. This region benefits from a maritime climate that provides cool winters, moderate summers, and high annual rainfall, despite orchards often being located on steep, erosion-prone slopes.
In the United States, nearly all commercial production occurs in Oregon’s Willamette Valley, which has a mild, temperate, maritime climate. The valley floor offers deep, fertile, well-drained soils, requisite winter chilling hours, and mild summers that prevent heat stress. Italy and Spain are also major producers, centered in regions featuring Mediterranean-like conditions, offering mild, wet winters and dry, warm summers.
Italy, the second-largest producer, has significant acreage in areas like the Lazio and Campania regions, where the climate supports high yields. These global centers highlight the need for a non-extreme climate. The winter must be cold enough for dormancy, but the spring must not be prone to severe, late-season freezes.
Selecting the Right Cultivar
Even when a location meets all environmental criteria, selecting the correct hazelnut cultivar is necessary for long-term success. European varieties (Corylus avellana) are valued for their large kernel size but are susceptible to Eastern Filbert Blight (EFB), a fungal disease that has limited production, particularly in eastern North America. EFB-susceptible European trees can be killed within five to ten years of infection, making them a high-risk choice in disease zones.
Modern breeding programs, such as those at Oregon State University, have developed blight-resistant cultivars like ‘Jefferson’ and ‘Yamhill’ that carry a single dominant resistance gene. These newer varieties allow for commercial production where EFB is endemic. Growers must also choose cultivars whose chilling hour requirements align precisely with local winter conditions to ensure proper bud development and maximum productivity.