What trees are hardy in the colder regions of the North? Which are recommended for the warmer South? These general questions are difficult to answer because hardiness is variable; each section of the country has its own definition. As gardeners, we are constantly learning what will and will not do in the areas in which we live. Nevertheless, there are certain trees that are considered hardy in regions where temperatures go well below freezing. For these sections, here are some of the more desirable kinds:
Birches. Graceful trees for containers. Clumps of the native gray, white or paper, or weeping European birches are desirable for the contrasting bark. Small leaves cast light shade.
Crab-apples. Lovely hardy flowering trees, with red, pink, purple, or white blossoms in spring and colorful fruits in fall, much favored by birds. The smallest one, which can be pruned to picturesque form, is the white-flowering Sargent crab-apple, as broad as it is tall. Choice hybrids include Dorothea, Dolgo, Flame, Hopa, and Katherine.
Dogwoods. Many kinds, including flowering dogwood, with white or pink flowers in spring, brilliant fall coloring, and interesting winter form. The Japanese kousa dogwood blooms later and continues for several weeks. For the West Coast, there is the upright Pacific dogwood. Cornelian cherry, a true dogwood, bears tiny yellow flowers in early spring.
Dove Tree or Davidia. Where reliably hardy (a specimen at Arnold Arboretum, Boston, blooms periodically), an unusual tree, with large white bracts among heart-shaped leaves in spring. Requires special care, but is worth the effort.
Franklinia or Gordonia. Like the dove tree, also requiring special attention. Single, camellia-like, cream-white flowers open in late summer and continue until frost. Leaves are colorful in fall. Barely surviving winters around Boston, this is reliably hardy from New York City southward.
Fringe Tree. Large shrub or small tree, with fluffy, white flowers appearing with unfolding foliage in late spring. Shows up strikingly against evergreens.
Ginkgo. One of the best, very hardy and slow growing with a fascinating form. Also called maidenhair tree, it transplants easily. A fastigiate variation, the Sentry Gingko, will give accent.
Golden-Chain Tree or Laburnum. Small ornamental tree with pendulous, wisteria-like, golden flowers in spring. It will attract much attention in a large plant box.
Golden-Rain Tree or Koelreuteria. One of few yellow-flowering trees for the North. Compound leaves are highlighted by upright panicles in midsummer, followed by
pods that change through several colors. Golden-rain withstands drought.
Hawthorns. Many kinds, with showy red, pink, or white flowers in spring. Outstanding is the English hawthorn, including the red Paul's Scarlet and Arnold hawthorn with white flower clusters. Washington thorn has bright red berries in fall.