Carya glabra aka Pignut Hickory

Pignut hickory, Carya glabra, is a deciduous tree in the walnut family, Juglandaceae. It grows wild from south-eastern Canada through the central and eastern United States. Its range runs from Maine down to Florida and reaches extreme southern Ontario. Other common names include smoothbark hickory, broom hickory and small-fruited hickory.

In gardens it usually reaches 50 to 65 feet (15 to 20 m) tall and 30 to 40 feet (9 to 12 m) wide. Forest trees can slowly climb past 100 feet (30 m), and one source cites 120 feet (37 m). The tree grows slowly and needs many decades to mature. It forms one straight trunk under a dense, oval to rounded crown. The branches leave the trunk at wide, strong angles and resist storm breakage.

Young bark is smooth and grey-brown. With age it develops scaly ridges that interlock in a diamond-like pattern. The twigs are hairless and brown, with small light brown buds. The leaves are alternate and pinnate, 8 to 12 inches (20 to 30 cm) long. Each carries five to seven toothed leaflets, and the end leaflet is the largest. New leaves open reddish or brownish in spring and turn glossy green in summer. In autumn they turn bright yellow.

The flowers appear in spring, around April to May, and have little ornamental value. Male flowers hang in yellow-green catkins 2 to 4 inches (5 to 10 cm) long. Female flowers form short spikes in small clusters at the branch tips. The fruit is a pear-shaped to oval nut, about 1 to 2.5 inches (2.5 to 6 cm) long. A four-part husk splits partway open as the nut ripens in early autumn. The kernels are edible but very bitter. Squirrels, other small mammals and birds eat them far more than people do.

The tree does well in full sun or partial shade. It prefers deep, fertile, well-drained soil that is on the acid side. It tolerates sand, clay and loam, and shows nutrient deficiencies on alkaline ground. Once established it copes well with drought and heat. It is hardy in USDA zones 4 to 9 and rated H6 in the UK. Seedlings quickly grow a deep taproot and dislike being moved, so plant young trees in their final spot.

Pignut hickory suits large gardens, parks and naturalised areas as a shade or specimen tree. It is a larval host for moths, including the hickory horndevil and the luna moth. The hard, strong wood makes tool handles and good firewood, and people use it for smoking meat. Falling nuts, twigs and leaves create litter and can dent cars, so keep the tree away from parking areas.

The tree has few serious problems. Hickory bark beetle can strike, mainly in drought years. Borers, pecan weevil, twig girdlers and fall webworms also feed on it. Occasional diseases include scab, powdery mildew, leaf spot, anthracnose, cankers and crown gall. The ASPCA lists the tree as non-toxic to dogs, cats and horses.