November 1998 Plant of the Month
Eastern redbud is a lovely small tree, notable for its early spring flowers, attractive foliage, and picturesque form. Native to the United States, redbud has a very wide natural range, from New Jersey south to Florida and west to Missouri and Texas. Redbud is a member of the pea family (Leguminoseae).
When selecting redbuds for the Upper Midwest, the plant's provenance, or seed source, is an important consideration. Because of redbud's wide native range, there is also a wide range of potential winter hardiness from different provenances. Trees grown from seeds that originated in South Carolina or Texas do not have enough genetic hardiness to survive in Minnesota or Wisconsin. Fortunately, there is a good seed-grown cultivar called 'Northland Strain' that has proven to be quite cold hardy. The provenance of the original tree of this strain is uncertain, but many of its descendants continue to grow at the Minnesota Landscape Arboretum and at numerous other places in the Upper Midwest. Redbuds growing near Columbus, Wisconsin provide another fairly hardy seed source. Even these hardy trees may have tip dieback or loss of flowerbuds during severely cold winters.
In its native woodland setting redbud may grow 20 to 30 feet tall. In most landscape settings it is somewhat shorter, and in the Upper Midwest heights of 12-15 feet tall a maturity are common. Redbud trees tend to branch fairly low to the ground, developing a broadly horizontal form with age. The form is upright to rounded when young. Redbuds are sometimes sold as "clumps", with usually three stems grown close together. The bark is smooth and gray when young, developing a scaly texture and orangish inner layers when mature.
Redbud puts on a spectacular floral show in the spring. Blooming before the leaves emerge, the branches are loaded with clusters of small pinkish purple flowers. Individually flowers are 1/3 to 1/2 inch long and have typical flower form of pea family members. Flower clusters are borne on virtually all stems, from the fine tips of twigs to the main truck itself. The flowers are effective for several weeks, usually in late April to early May in the Twin Cities area.
Seed pods then develop over the summer, turning from celadon green to brown in early fall. The flat pods are 2-3 inches long and 1/2 inch wide and contain small, hard-coated seeds. The pods often persist on the tree through the winter.
Redbud has nice foliage during the growing season. The heart-shaped leaves emerge in spring glossy and often with a purplish blush. The leaves are medium to dark green during the summer, and usually develop a good clear yellow fall color, though they may drop green if there are early frosts. Individual leaves are fairly large, up to 5 inches in both length and width.
While redbuds prefer a deep, moist, yet well drained soil, they will actually tolerate a fairly wide range of soil types and pH levels. Do not plant them in perpetually wet soils, however. An ideal site for redbud is in light shade or part-day shade, but full sun is also acceptable. Transplant redbuds in the spring; balled and burlapped, container, and bareroot trees are available. A large swath of organic mulch such as wood chips or shredded leaves will help keep soil moisture in the root zone and protect the trunk from lawnmower damage. This may also help prevent the two most serious disease problems of redbud, stem cankers and verticillium wilt. Insects are rarely a problem on redbud.
The informal appearance of redbud lends itself to naturalistic landscaping. Redbuds make a lovely understory planting at the edge of a woods, perhaps mixed with amelancliers. They can also add a rustic charm to more urban settings, and their size fits well in small lots. Redbuds can be used as individual specimens or in small groups. Their bright spring flowers combine well with masses of bulbs such as yellow and white narcissus, or white, pink, and purple tulips.
By Nancy Rose, Minnesota Landscape Arboretum