Hazelnut ‘Barcelona’ is a vigorous grower and an excellent producer of large nuts. The nuts ripen from red-orange to brown in late-summer to early-autumn. Other hazelnut trees such as Hazelnut ‘Butler’, Hazelnut ‘Merveille de Bollwiller’, and Hazelnut ‘Tonda di Giffoni’ can serve as pollinators. Hazelnut trees thrive in mild summers and cool winters and require protection from high summer temperatures and wind. The ideal annual average temperature is between 12°C and 16°C, with a maximum of 35°C to 36°C and a minimum of -8°C to -10°C. Annual rainfall of 800mm to 1000mm, spread evenly throughout the growing season, is ideal. In areas with prolonged dry periods from late-spring to mid-summer, particularly in free-draining soils (sandy or stony), irrigation will be required. Hazelnut is evergreen and native to Europe and western Asia. Learn more about Hazelnut . Hazelnut ‘Barcelona’ is an old cultivar widely distributed in Western Europe and probably originated in Spain. Hazelnut ‘Barcelona’ has been the main cultivar grown in Oregon, United States since the mid-1800s.