Upright trunks and a rather open-branching and leaved canopy describes many different types of birch trees (Betula spp.). A common sight in forests in Canada, Scandinavia and the Himalayas, birch trees have gained popularity for use in gardens as ornamental specimen trees or to create picturesque groves. Some species of birch are cut down for their wood. Birch wood is often utilized to build doors and windows, flooring, cabinetry, interior molding, wood paneling, furniture and plywood.
Worldwide, there are between 50 and 60 different species of birch trees. The birches that attain a more classic tree-like habit (some species are shrubs) range in mature height as short as 15 feet to as tall as 70 feet, according to the American Horticultural Society's "A-Z Encyclopedia of Garden Plants." A list of some species of birch trees grown in garden settings include:
Chinese paper birch (Betula albosinensis) Yellow birch (Betula alleganiensis) Erman's birch (Betula ermanii) Japanese cherry birch (Betula grossa) Sweet birch (Betula lenta) Monarch birch (Betula mazimowicziana) Transcaucasian birch (Betula medwedewii) Black birch (Betula nigra) Paper birch (Betula papyrifera) European white birch (Betula pendula) Asian white birch (Betula platyphylla) Gray birch (Betula populifolia) Downy birch (Betula pubescens) Schmidt birch (Betula schmidtii) Szechuan birch (Betula szechuanica) Himalayan birch (Betula utilis)
All birches are native to the temperate, boreal or Arctic regions of the Northern Hemisphere. In Asia, the various tree species grow naturally in Afghanistan, China, Japan, Kazakhstan, Korea, Kyrgyzstan, Mongolia, Nepal and Russian Siberia. Other birches hail from Europe and North America, with some species occurring in the cooler montane regions of Central America and the northern Andes in South America. Birch trees reside in woodlands, moors, mountains and heathlands.
Birch trees are deciduous, lacking foliage in winter. The leaves are typically oval in shape with a tapering tip and serrated edges. They range in color from medium to deep green and attain yellow to gold hues in autumn before falling from the tree. In early spring, just before new leaves emerge, the birch produces male- and female-gendered flowers on separate branches of the same plant. The tiny flowers are yellowish-tan to yellow-brown in color. Male flowers occur in a pendant cluster called a catkin and are much longer than the similarly colored female flowers, which are at first held upright before drooping. A birch tree filled with male flowers is ornamentally pretty to see. Pollination is done by the wind. The fertilized female catkins yield tiny, two-winged seeds (nuts) called samaras. Most birch trees produce a thin, papery, exfoliating bark that is white, gray or brown.
While there are exceptions, generally birch trees grow best in climates that have cool to warm summers, not hot. Plant a birch tree in a moist soil that has some fertility but also drains well after rains. They excel in full sun exposures where summers are cool, but should be partially shaded in warmer summer landscapes. Moreover, some species of birch trees that are smaller in size and native to woodlands must have partially shaded light exposures as well as protection from sweeping winds, according to the "A-Z Encyclopedia of Garden Plants."
Many different fungi are known to cause problems on birch trees. Leaf spot, anthracnose, rust and wood rot, canker and twig die-back are fungus-related susceptibilities. Plant viruses can harm trees, too. Insects of concern include borers, leaf miners, aphids, leafhoppers and caterpillars/larvae. The bronze birch borer in particular disrupts sap flow on birch trees grown in North America, as well as obliteration of foliage by the hungry larvae of gypsy moths.