Running bamboos have leptomorph rhizome systems, characterized by long, thin rhizomes that grow horizontally and spread quickly; they can become invasive if not controlled properly. The culms, or stems, of running bamboos are generally wider than the rhizomes they develop from. Many running bamboos grow well in temperate climates. Clumping bamboos have a pachymorph rhizome system, which is composed of short, thick rhizomes that produce culms smaller in diameter than the rhizomes. Clumping bamboos are noninvasive because their rhizome systems expand very slowly each year and the culms grow in a close clump.
Most clumping bamboos are tropical, but the genus Fargesia grows in temperate climates and some of its species are hardy down to -20°F, although they don't grow well in exposed, sunny locations. "Clumping bamboos are mountain bamboos, so they do not do well in full sun, because they are an understory plant in their native environment," says Susanne Lucas, past president of the American Bamboo Society. Lucas suggests planting clumping bamboos on the north side of a house or in a woodland setting where they can be used as an understory plant. If you're looking for a very hardy, shade-tolerant specimen plant, Lucas suggests umbrella bamboo (Fargesia murielae), which grows to 10 to 12 feet and is hardy to USDA Plant Hardiness Zone 5. F. robusta is not as cold-hardy but tolerates more sun and grows to 15 feet.
Running bamboos offer temperate gardeners a wider variety of culm and foliage colors, sun tolerance, and height ranges, but their aggressive rhizome systems must be contained within a physical barrier, such as a brick or concrete planter or a specialized plastic rhizome barrier. If you're not willing to install and maintain a barrier, stick with a noninvasive clumping bamboo. To learn more about bamboos and rhizome barriers, check out the American Bamboo Society's Web site (www.bamboo.org). It has fascinating information about bamboos that grow in temperate climates, as well as an extensive list of bamboo nurseries and resources around the country.