Hazelnut - Corylus avellana

Common Names: Hazel, hazelnut, hazel nut, European hazel, common hazel, common filbert, European filbert, cobnut, corkscrew hazel, Harry Lauder's Walking Stick, Haselnuss, Haselstrauch, noisetier, noisette, noisettes, noisetier commun, noisetier du Japon, avellana, avellano, coudrier, Avelinier, aveleira, Corylus heterophylla, nut, Corylus avellana

Latin Name: Corylus avellana

Origin: Africa, Asia, Europe, South America, North America

Short Introduction

Hazel is an easy-to-grow shrub that thrives with minimal care. Standard soil is generally sufficient, though some horticultural sources recommend medium fertility, with a preference for humus-rich to sandy soils. Both nutrient-poor and over-rich soils are less suitable. High soil acidity is not optimal; hazel does best in alkaline conditions (pH 4.5–8.5) with adequate moisture. Hazel is relatively resistant to wind, pollution, and winter but is less tolerant of extreme frost.

Hazel can be cultivated for agricultural purposes or as an ornamental plant along property borders. While it is self-fertile, planting several hazel plants together increases yield. Notably, hazel is often targeted by small pests, squirrels, and birds (particularly those in the crow family), potentially resulting in significant crop loss.

The best time to plant hazel is usually during the harvest season, in autumn. Seeds germinate at the end of winter or the beginning of spring. For indoor propagation, soak seeds in warm water for 48 hours, then keep them warm for around two weeks before stratifying in cool conditions; germination takes one to six months at around 20°C (68°F).

During the first winter, it's advisable to plant seedlings in individual pots and let them grow in a cool frame or a sheltered outdoor spot. They may also be started in soil-filled trays. In late spring or early summer, transplant to a permanent location and layer in autumn. Hazel can also be propagated via cuttings or grafting.

Commercial hazelnuts are cultivated for their nuts in Europe, Turkey, Iran, and the Caucasus. The world’s largest producer is Turkey, especially in Ordu province, where annual production is around 625,000 tons—approximately 75% of the global supply.

Detailed Description

A traditional nut valued in folk medicine, cuisine, and woodworking.

Botanical Information

Hazel (Corylus avellana) is a typically broad, deciduous shrub reaching a height of 3 to 8 meters (with a recorded maximum of 15 meters). Its crown is round and irregular, with a maximum width of up to 10 meters at the highest point. The bark is smooth, brownish-gray, and may develop cracks with age. Hazel can live for 80 to 100 years. Leaves are oval to ovate, alternate, 6–12 cm long and wide, softly hairy on both sides, with a double-serrated margin and a pointed tip. The petiole is 1–2 cm long.

A well-branched root system develops strong lateral roots near the surface, with average lengths of 3–4 meters. The densest root network lies 30–50 cm deep, making hazel a vigorous competitor for nearby crops. Hazel forms interesting ectomycorrhizal relationships with several truffle and other fungal species.

Hazel flowers in spring, often from February to April, before leaves emerge. Flowers are monoecious and unisexual: male flowers are wind-pollinated catkins (yellow or red), while female flowers are inconspicuous buds with purplish-red stigmas.

The fruit is the well-known hazelnut, clustered singly or in groups of up to five, each nut about three-quarters enclosed in a tough, bell-shaped, green to brownish husk formed by fused bracts. Hazelnuts are oval, 15–25 mm long, 12–20 mm wide, yellow-brown to brown with a pale scar at the base. When mature at the end of summer (about 7–8 months after pollination), the nut drops from the husk.

Origin and Distribution

Hazel is native to Europe and parts of Western Asia. Its range covers most of Europe (from the British Isles north to Norway and the Arctic Circle), parts of Asia Minor (from Greece to Turkey and Cyprus), Syria, Northwestern Iran, and North Africa, also introduced in North and South America and the Caucasus. Hazel is a typical pioneer species on non-forested soils.

Throughout the Czech Republic and Slovakia, hardy hazel is widespread from lowlands up to submontane areas, commonly found on woodland margins, in thickets, clearings, and along roads and waterways, except at higher elevations where it is less common. The upper altitude limits reach about 800 m in the Ore Mountains, 1200 m in the northern Alps, and about 1,600 m in Carinthia.

Usage / Dosage

Historically, hazel leaves were the most commonly used part in herbal practice, usually harvested in July, though leaves and nuts contain similar active compounds. Leaves provide tannins, glycosides, and essential oil, traditionally used to support the digestive system—offering antidiarrheal, diuretic, and astringent effects (e.g., for intestinal inflammation).

Hazel is deeply rooted in mythology and folklore as a symbol of wisdom. In Greek myths, Hermes’ caduceus was crafted from hazel. Norse god Odin was said to carry a hazel staff, as did Celtic druids and judges. Thor’s axe handle was also made of hazel. Hazel branches were associated with rituals relating to the underworld and the afterlife, including burial customs among Celts, Alamanni, and other Germanic tribes.

Hazel has long been a favored component of traditional hedges in the flatlands of England, cultivated as an understory plant, for basket-weaving, and in wooden farm buildings. Hazel wood is soft and bendable, still valued in woodcraft, basketry, and folk arts. Formerly, it was also used in furniture making.

The plant is mainly cultivated for its nuts, which are consumed raw, roasted, or baked, or processed into hazelnut paste. Hazelnuts are popular in confectionery, especially in chocolate production. Hazelnut oil finds uses in cosmetics and painting.

Hazelnuts are key ingredients in pralines, chocolates, and pastries, especially in products made with hazelnut paste. In Austria, hazelnut paste is a staple in cakes like the famous Vienna cake. In Kyiv cake, hazelnut meal is used in the meringue and also decorates the sides. The French dacquoise contains a hazelnut layer. Hazelnuts are also widely used in Turkish and Georgian cuisine (e.g., churchkhela, satsivi sauce). Hazelnut is the main ingredient in the Italian vodka-based liqueur Frangelico.

Folk tradition regards hazel as protective against black magic, natural disasters, and snakes. Legend says St. Patrick used a hazel staff to drive snakes from Ireland. Witch trial records note the use of hazel in rituals for rainmaking. Hazel was also associated with fertility; hanging a hazel branch over the marital bed was believed to boost fertility and resolve marital issues. In German, the phrase "in die Haseln gehen" (to go into the hazel bush) means to court or woo.

Medicinally, hazelnuts are traditionally used to lower total plasma cholesterol and as an antioxidant agent. Folk healers recommend regular hazelnut consumption to prevent kidney stones and alleviate symptoms of untreated conditions.

Folk medicine suggests a hazelnut-rich diet or regular hazelnut consumption in older adults and younger people to help reduce high plasma cholesterol. Traditional medicine in Turkey and Kurdish regions also values their antioxidant properties.

Historically, hazelnuts were given to treat diarrheal conditions as an astringent (like activated charcoal), for cleansing, and as an antihelminthic for intestinal worms—especially pinworms and roundworms in children—as well as for digestive issues linked to gastrointestinal discomfort. Scandinavian herbals recommended hazelnuts as a diaphoretic (to promote sweating), tonic, and a highly nutritious ingredient.

Analysis of aqueous extracts of several hazel species, including common hazel, with reverse-phase HPLC-DAD, revealed interesting phenolic compounds with antioxidant capacity. Antioxidant potential was measured via chemical reduction and radical scavenging (DPPH and beta-carotene linoleate tests), showing significant dose-dependent antioxidant activity. Gram-positive bacteria were found sensitive to certain compound concentrations (MIC 0.1–1.0 mg/ml).

The same compounds were tested for antimicrobial activity against gram-positive bacteria (Bacillus cereus, B. subtilis, Staphylococcus aureus), gram-negative bacteria (Pseudomonas aeruginosa, E. coli, Klebsiella pneumoniae), and fungi (Candida albicans, Cryptococcus neoformans).

Active Compounds

100 grams of hazelnuts supply approximately 630–650 calories and are a rich source of essential nutrients—particularly protein, digestible fiber, thiamine, vitamin E, folic acid, manganese, magnesium, and phosphorus (covering about 30% of daily needs). Smaller but significant amounts (10–20% of daily needs) include vitamin K, niacin, riboflavin, lutein, zeaxanthin, calcium, sodium, iron, copper, and zinc. Hazelnuts are also rich in fats.

Total fat content (about 93% of daily requirement) consists of monounsaturated oleic acid (75% of total), polyunsaturated linoleic acid (13%), and saturated fatty acids—palmitic and stearic acids—accounting together for 7%. This makes hazelnuts a high-energy food (recommended for hikers, trekkers, and cyclists). For athletes, combining them with figs, dates, or raisins helps supplement carbohydrates.

Tannins in both hazelnut kernels and leaves include several identified compounds: 3-, 4-, and 5-caffeoylquinic acid, caffeoyltartrate, p-coumaroyltartrate, myricetin-rhamnoside, quercetin-3-rhamnoside, kaempferol-3-rhamnoside, p-coumaric acid, and three derivatives each of myricetin and quercetin, among others. Tannins, glycosides, and essential oils have broad digestive applications, with antidiarrheal, diuretic, and astringent effects (for intestinal inflammation).

Traditional Dosage

No specific sources describe optimal dosage.