Betula nigra aka River Birch

River birch, Betula nigra, is a deciduous tree in the birch family, Betulaceae. It grows wild across the central and eastern United States. Its range runs from southern New England to Florida. It extends west to Minnesota, Nebraska, Kansas and Texas. In the wild it sticks to moist ground such as stream banks, swampy bottomlands and floodplains. Other common names include red birch, water birch and black birch.

In gardens it usually reaches 40 to 70 feet (12 to 21 m) tall. Some sources cite 90 feet (27 m) for the largest wild trees. Spread runs from about 25 to 60 feet (8 to 18 m). Young trees are oval or pyramidal, and older trees develop a rounded or irregular crown. Many specimens grow with several trunks that split low down. Growth is fast.

The bark is the main attraction. On young wood it is smooth, shiny and reddish-brown. It soon peels in thin papery sheets of salmon, cinnamon and creamy orange. The loose layers stay attached and give a shaggy look in winter. Very old trunks turn brown and break into scaly ridges. The leaves are alternate, simple and roughly diamond-shaped, 1 to 4 inches long. They have doubly toothed edges and are glossy dark green above and paler beneath. In autumn they turn yellow, but the colour is brief and the leaves drop quickly.

Male and female flowers grow in separate catkins in spring, from about March to May. The brown male catkins reach 2 to 3 inches long and often hang in threes. Wind carries their pollen. Small cone-like fruits, 1 to 1½ inches long, hold many winged nutlets. Grouse, turkeys, small birds and rodents eat the seeds. Birds and squirrels feed on the male catkins in late winter.

River birch handles heat better than most birches and suits hot, humid summers. It grows in full sun or part shade and prefers moist, acidic soil. It also copes with clay, poor drainage, flooding and some drought. Leaves yellow with iron chlorosis on soils above pH 6.5. It is hardy in USDA zones 4 to 9 and rated H7 in the UK. Prune only when dormant, because the sap bleeds in spring. Gardeners plant it as a shade or specimen tree, in rain gardens and along ponds and streams. Its spreading roots help hold stream banks against erosion. It drops many twigs, so keep it away from house gutters.

This birch resists the bronze birch borer far better than its relatives. Aphids, leaf miners, birch skeletonizer and lace bugs may still appear. Leaf spot can be a problem in wet years, and honey fungus, rust and powdery mildew are possible. In some urban sites trees live only 30 to 40 years, often from too little water. Large old trunks can decay. In early spring people tap the trunk for a sweet sap. They drink it fresh, boil it into syrup or brew it into birch beer. Birch tar can irritate skin.