Hazelnuts are the edible nuts produced by woody plants belonging to the genus Corylus. This genus, part of the birch family Betulaceae, includes species that grow as both multi-stemmed shrubs and single-trunk trees. Hazelnuts are a significant crop cultivated across the temperate Northern Hemisphere.
The Hazelnut Plant’s True Identity
The plants that produce hazelnuts, known collectively as hazels, are classified in the genus Corylus, which comprises deciduous shrubs and small trees. Most commercially grown hazels, such as the common European hazel (Corylus avellana), naturally grow as a multi-stemmed shrub, often reaching heights of 10 to 20 feet. This form is characterized by multiple suckers emerging from the base of the plant.
The hazel plant is monoecious, meaning individual male and female flowers are found separately on the same plant. Male flowers appear as elongated, pendulous structures called catkins that release pollen in late winter or early spring. Female flowers are much smaller, often looking like tiny buds with only a few bright red styles protruding. Once pollinated, the fruits mature into a hard-shelled nut encased within a leafy outer wrapping, known as an involucre or husk.
The distinction between a hazel shrub and a hazel tree depends on species and cultivation method. While many species are naturally shrubs, others, like the Turkish Hazel (Corylus colurna), grow into large, single-trunk trees. Even shrub varieties can be pruned and trained to grow with a single trunk, a common practice in commercial orchards to facilitate mechanical harvesting.
Commercial Growing and Harvesting Methods
Large-scale hazelnut production is concentrated globally, with Turkey being the leading producer, followed by Italy and the United States, particularly Oregon. Harvesting methods depend on the climate and the specific variety grown. In many commercial orchards, plants are managed to allow the nuts to fully ripen and naturally fall to the ground.
Once the nuts have dropped, mechanical harvesters collect them from the orchard floor. These specialized machines use sweepers to gather the nuts into rows, followed by a vacuum or pickup system to lift the nuts and separate them from debris. This ground-collection technique is most effective in regions with a dry harvest season, such as Oregon’s Willamette Valley.
In areas with wetter climates or for certain hybrid varieties, farmers use straddle harvesters that pass directly over the shrub to shake or slap the nut clusters from the branches. This method collects the nuts before they fall to the ground, which is necessary when husks do not fully release the nut or when ground conditions are too damp. After collection, the nuts must undergo a post-harvest drying process to reduce moisture content before they are shelled or shipped for consumption.
Common Varieties Available to Consumers
The term “hazelnut” is the general name for all nuts produced by the Corylus genus, but consumers may encounter various cultivated names. Filbert and Cobnut are two common terms that historically referred to specific types, though they are often used interchangeably today. A Filbert traditionally describes a nut where the leafy husk completely covers the nut, often associated with species like Corylus maxima.
A Cobnut typically refers to a cultivated hazelnut variety, particularly in Britain, and denotes a nut harvested fresh while its husk is still green. These fresh cobnuts are usually eaten raw and possess a sweeter, juicier texture before drying. Commercially available hazelnuts are mainly derived from the European species Corylus avellana and its numerous cultivars, which differ in size, shell thickness, and flavor profile.