Part of the birch family, the 13 species of hazelnut trees comprise the genus Corylus, members of which can be found spread around most parts of the world. While the two native American species produce flavorful nuts, it is the Turkish hazelnut that appears most often in holiday nut bowls. In the home garden, the hazelnut's spreading habit makes it useful as a barrier shrub. The tree can also be trained to a single stem.
Types of Hazelnut Trees
The American filbert (Corylus americana) is one of two native American hazelnut species. The second, the beaked hazelnut (C. cornuta) is very similar in growth habit, fruit production and quality, and both were used by native peoples as well as animals as a valuable and tasty food source. Turkish hazelnut (C. colurna) and giant hazelnut (C. maxima) are the two primary species used for commercial nut production in Turkey, Italy, Spain and the United States. The common or European hazelnut (C. avellana) is popular for both nut production and as a landscaping shrub.
Though the individual species vary in height from 15 to 45 feet, hazelnuts in the wild usually form dense thickets of shrubby bushes. The tree has many distinctive identifiers: serrated heart-shaped leaves that, along with the twigs, feel rough and hairy to the touch; dangling flowers called catkins that appear on male shrubs in the spring; and the nut clusters that are four or five to a cluster and hide the milky brown filbert inside shaggy green, bell-shaped casings. Spring blossoms on female trees are inconspicuous.
Wild American hazelnuts, when left uncultivated, will form a reasonably dense thicket. To prevent unwanted spread, the shrub should be suckered as new shoots appear from the parent plant. Additionally, individual plants can be trained to grow on one trunk. Fall foliage is spectacular, with leaves turning a flaming red. The tree's harvest of nuts matures from August to September, and the nuts can be eaten directly off the tree.
Tree Care and Culture
Hazelnuts prefer to be situated in full sun to partly shady locations in rich, well-drained soil. However, they are excellent candidates for locations that are difficult to plant, and will perform well in hot, dry sites once established. Trees withstand pruning at any time of year.
Pests and Diseases
Commercial production of hazelnuts along the Atlantic seaboard of the United States has been stymied by eastern hazelnut blight, which is caused by the native fungus Anisogramma anomola. While the fungus forms insignificant and mostly harmless cankers on the stems of American hazelnuts, it is a serious killing pest of European and Turkish hazelnuts when planted in the eastern half of the United States. If left untreated by systemic fungicides, plants die within 10 years.
Several insect species are also known pests of hazelnut trees, including tent caterpillar, Lecanium scale, hazelnut leafroller, filbert aphid and filbertworm. Because damage is mainly confined to the foliage, infestations generally maim rather than kill. Typical symptoms include reduced vigor and nut production.