Hazel nuts grow as small trees or large shrubs, depending on the species. Corylus americana, or American hazelnut, resembles a shrub. Hybrids of C. avellana, or the European hazelnut, are the most commercially valuable, according to the University of Minnesota.
Oregon is the largest grower of commercial hazelnuts, but there are several native species that are scattered throughout the United States. These small trees tend to grow as understory trees and produce small nuts with thick shells. They grow most rapidly in moist, fertile soils in areas with cool summers and mild winters, according to the University of Tennessee. Poor, dry soils cause growth to be slowed and the tree to become stunted.
Hazel nut trees have thick, dense canopies and broad leaves with toothed margins. American hazelnuts can grow up to 18 feet tall and are rated as a medium-to-fast growing tree by the Arbor Day Foundation. European hazelnuts grow to 25 feet and are rated as fast-growing trees.
In some fast-growing trees, rapid growth does not translate to fast fruit production. This is not the case with hazel nut trees. These small trees can reach maturity in as little as three years, according to the University of Minnesota. Maturity is defined as being able to produce a crop of nuts.