Hazel is classified in the order Fagales, tribe Corylaceae, genus Corylus. The genus currently includes 25 species among which the most important is Corylus Avellana (common hazel). It presents the appearance of a large, bushy shrub than a tree, from the number of suckers thrown up by the root. The trunk has smooth and compact bark; the wood is tender and pliant; branches are dotted with numerous lenticels; the cordate, dark green leaves are simple and alternate with serrated margins and pubescence on petiole. Both vegetative and mixed buds are formed in the axil of the leaves. The terminal position of the mixed buds is characterized by the presence of the dark red hairy styles that emerge from perules in the months from December to February. The groups of one to five catkins also burst out from the axil of the leaves. They appear in June but are fully developed in the pollen emission period, i.e. from December to February. The fruit of the hazel is a globose-ovoid nucula. Its seed is edible and has a high oil content. The root architecture exceeds the crown width and grows down in deep, principally in the first 50 cm depending on the nature of the soil and the cultivation techniques.
La "tonda gentile romana"
This hazelnut variety is roughly spherical to oval in shape, with a slightly pointed tip, between 14 and 25 mm in calibre. The shell is of medium thickness, hazel in colour, moderately shiny, with scattered pilosity at the tip and clear striation. The nut is small to medium in size, of a variable subspherical shape, similar in colour to the shell, mostly covered in fibres, with a corrugated surface and quite clear grooves. The perisperm is solid in consistency and crunchy; the flavour and aroma are fine and lingering. Shelled hazelnuts can be consumed raw, dried or roasted. Hazelnuts also come whole, chopped or ground and are suitable for cake, biscuit and ice cream making as well as cream and liqueur preparation. Ideal soils for hazel groves are loose, fresh, acid and rich in organic substances; the training system depends on the type of cultivation: shrubs, vase-shaped and single-stemmed trees. Pruning takes place each year.Allowed planting density per hectare is 150 for the old trees and 650 for the new seedlings. Average annual production is 4 tons per hectare through irrigation system and 3 tons per hectare through dry farming. The harvesting of hazelnuts can be done manually or mechanically. Harvesting time is from mid-August to mid-November. Hazelnut crop harvest is followed by storage of the hazelnut crop in suitable premises with good ventilation and with no more than 6% relative humidity. Sorting, grading, treating and conserving must be carried out within one year following the harvest. The yield after shelling is between 28% and 50%. Hazelnuts are very high in energy and loaded with monounsaturated fatty acids, vitamin E and vitamin K, choline and minerals (potassium, calcium and phosphorus). In order to understand the importance of hazelnut production for the economy of the Viterbo area, suffice is to say that the agricultural area devoted to cultivation of hazelnuts accounts for over 14% and represents the third more widespread cultivation, after durum wheat (41,4%) and olive (17,4%).