Hazelnuts Hazelnuts grow in clusters on the hazelnut tree in temperate zones around the world. The outer husk opens as the nut ripens, revealing a hard, smooth hazel colored shell. Depending on the area of the world, they are either hand-picked or mechanically harvested.One of the oldest agricultural crops, hazelnuts are believed to have originated in Asia and then moved into Europe. They were taken to the U.S. by Europeans in the 1850s. Today, the principal hazelnut producing countries are Turkey, Italy, Spain and the U.S.Also known as filberts and cobnuts, these sweet, rich, grape-size nuts are marketed in the shell or as kernels which may be roasted, natural or further processed into diced, sliced, meal, paste or butter. Hazelnuts are mainly used in confectionery and baking. However, they can also be found in salads, sides, main dishes, ice cream and as snack items.