Corylus avellana aka Common Hazel

Corylus avellana is the European hazel, also called cobnut or filbert. This leaf-shedding shrub belongs to the birch family, Betulaceae. It grows wild in Europe, western Asia, and northern Africa. Wild plants grow along woods, streams, and hedges. Most garden plants reach 12–20 feet (3.7–6.1 m) tall. Their spread can reach 15 feet (4.57 m). RHS gives a broader size range, reaching 26 feet (8 m). Hazel can also form a small tree with several trunks.

Upright stems rise from the roots and form a rounded crown. New root shoots allow the plant to build a thicket. The smooth bark ranges from pale brown to gray-brown. Fine, stiff hairs cover the slender, zigzag twigs. Broad green leaves grow in turn along each stem. They have soft hairs and edges with two sizes of teeth. Leaves turn yellow in fall, though UConn also reports reddish tones. The bare stems and hanging catkins give the plant winter interest.

Male and female flowers grow on the same plant. They open before the leaves, mainly from February to March. Male flowers form hanging yellow catkins on the bare branches. The tiny female flowers show little beyond their red styles. Nuts grow in groups of one to five. A short, leaf-like husk surrounds each rounded brown nut. The nuts ripen from late summer into fall. Birds, squirrels, and field mice eat them. Bees visit the flowers for pollen. People eat the nuts, including after roasting them.

Grow hazel in sun or part shade with good drainage. Moist soil rich in organic matter suits it best. It also grows in average garden soil. UConn reports that it copes with poor, dry sites. Neutral or alkaline soil suits it, including chalky ground. Missouri Botanical Garden advises against heavy clay. The plant grows in USDA zones 4–8 and has RHS rating H6. Use it for hedges, screens, shrub borders, or woodland edges. Remove root shoots when a spreading thicket would cause problems.

Eastern filbert blight is a key disease risk. Other problems include leaf spot, crown gall, and black knot. Honey fungus, silver leaf, and powdery mildew may also occur. Japanese beetles can damage the leaves. Aphids, scale, caterpillars, gall mites, and sawflies may attack plants. Squirrels can reduce the nut crop. The sources confirm edible nuts but give no species-level toxicity assessment.