Birch Trees in the Summer

Catkins form throughout the summer and generally start falling in August.Jupiterimages/liquidlibrary/Getty Images

Birch trees occur primarily in the northern regions of North America, and you can distinguish them from other trees by the distinctive "cross streaks" on their papery-looking bark. Leaves have double-toothed edges, meaning that edges are jagged, and each tooth contains an additional tooth on it, explains George Petrides, author of the Peterson field guide "Eastern Trees." In the summertime, birch trees wear lush green foliage and produce flowers on strands called catkins.

Paper Birch

The paper birch (Betula papyrifera), also known as the American birch, extends from east to west across the northern United States and Canada. The paper birch's summer foliage includes leaves that are 2 to 4 inches in length with a broad base tapering off into a sharp point. The base of the leaf may appear flat or heart shaped. Like all birches, the leaves are double-toothed. Leaves emerge singly from the twig, alternating sides as they progress down the branch. The paper birch produces seeds on catkins--strands 1 to 2 inches long that contain multiple tiny seeds--that fall to the ground in late summer. Although a popular ornamental tree because of its white bark, the University of Connecticut Horticulture Department warns that the paper birch cannot tolerate hot summers, restricting its range to regions with milder summer weather.

The sweet birch (Betula lenta), also know as the black or cherry birch, reaches farther south than the paper birch, occurring primarily in the Appalachian Mountains. Oil from the leaves is used in birch beer and in place of the wintergreen flavoring commonly used in gums and toothpastes. Summer foliage of the sweet birch resembles that of the paper birch, but leaves may reach 6 inches in length. Catkins also drop in the late summer. Sweet birch catkins do not droop from the branches but extend upward and have a stouter appearance. The Purdue University Department of Horticulture recommends late summer as the best time to plant sweet birch seeds, when they're normally dropping to the ground from catkins.

The river birch's peeling bark distinguishes it from its relatives.Close-up of a river birch tree image by ryasick from Fotolia.com

The river birch (Betula nigra) ranges the farthest south of any birch species, according to the U.S. Forest Service, where it reaches into northern Florida and extends as far west as eastern Texas. You can identify the river birch by its many-colored bark that peels from the trunk in large sheets. The summer foliage of the river birch resembles that of other birch species, with leaves growing up to 5 inches long. Unlike its northern relatives, the river birch does not drop seeds in late summer into fall. Instead, at the end of the summer, the catkins ripen and remain on the tree through the winter before seeding the following spring. The catkins you see on the tree at the end of summer appear upright and cylindrical and remain green.