Uncommon Small Flowering Trees
Originally published in the Ithaca Journal, July 2003
By Mary Hirshfeld
When most gardeners think of small flowering trees, species like crabapples, flowering cherries, and dogwoods immediately come to mind. And indeed, all of these trees offer a wide array of cultivars, providing pleasing variations in flower and fruit color, tree size and shape, and even foliage color. But if you are thinking of "branching out," many less familiar yet equally pleasing small ornamental trees are available to provide color before the crabapple, cherry, and dogwood season begins, as well as after it's over.
Despite the fleetness of their flowering, amelanchier, or serviceberry, remains one of my favorite small trees. Every May, I treasure the few short days when their clouds of white blooms billow from hedgerows and the wooded edges of farm fields. During a cool spring, such as the one we recently experienced, their blooms hold on for a good 10 days, but these are usually shed quickly with the first unseasonably hot day. The thicket serviceberry (Amelanchier canadensis) is a lovely, multiple-stemmed, large shrub, but in the nursery trade it is frequently confused with the more arboreal Allegheny serviceberry (A. laevis). The names often are used interchangeably, so whether you're getting a tree or shrub when you purchase a plant under either name remains a gamble. If you want to be sure, stick to named cultivars. The most highly recommended of these is 'Autumn Brilliance', a selection of A. x grandiflora, itself a hybrid of A. arborea and A. laevis. A strong grower, this tops out at around 25 feet, producing masses of fleecy white flowers in late April, followed by juicy blue-black berries that are favored by robins and cedar waxwings. Fall color is an electric combination of orange, purple, and red, with the leaves falling to reveal graceful delicate, silver-gray branches. 'Princess Diana', a selection from Wisconsin, and 'Ballerina' from the Netherlands are two additional top-notch selections, both with profuse flowers, sweet berries, and brilliant red fall color.
A lovely, elegant June-flowering small tree is the Japanese snowbell (Stryax japonicus). Reaching 20 to 25 feet in height, the Japanese snowbell can spread its horizontally tiered branches even wider. Its gray bark, and strong horizontal branching patterns provide winter interest and create interesting shadows on the snowy ground. Flowers are crystalline white, five-pointed pendulous bells, borne in profusion along the length of the branches. These are followed by elegant, oval, grey-brown seed capsules that dangle on long stalks, accentuating the branching pattern. The Styrax available from nurseries is seed-grown, so individuals vary slightly in their height and form. If you prefer to know exactly what your selection will look like, you can choose from several cultivars. 'Emerald Pagoda' is somewhat more upright in habit, with larger leaves and flowers than most. 'Pink Chimes' is also more upright with soft pink flowers, and 'Carillon' is a small round-headed weeping tree. The fragrant snowbell (Styrax obassia) is less commonly seen, and long had a reputation of being hardy only as far north as zone 6. However, trees at Plantations have proven to be reliably hardy in zone 5, even coming through the extremes of last winter with minimal dieback. Leaves are very large and rounded, often obscuring the flowers a bit, but providing a welcome bold texture unusual in a small tree. Far more upright in habit than Styrax japonicus, the fragrant snowbell comes into flower a bit earlier as well, displaying small white bells held in slender pendulous clusters. Both species perform best in a site protected from wind, bright sun, and winter extremes, and are happier as understory trees than in full sunlight.
If you're looking for a bit of floral excitement later in the summer, try the Korean evodia (Tetradium Danielle, formerly Evodia); the golden rain tree (Koelreuteria paniculata); or the seven-son flower (Heptacodium miconioides). Korean evodia is a fast-growing tree that tops out at about 30 feet here in Ithaca, although specimens further south can attain 50-foot heights. Evodia benefits from a protected site, especially in youth, when it can suffer dieback in severe winters. Usually multiple-stemmed, evodia can be a bit gawky when young, its fast growth rate resulting in long internodes, which produce sparely branched limbs. However, with age it usually bulks up into a nice round-headed tree. Its long, glossy, green leaves are pinnately compound and attractive; although fall color is lacking, they remain rich and lush throughout the summer. Evodia is a member of the rue family, and like the common herb, produces sharp-smelling oils most noticeable when a leaflet is bruised. It is perhaps this unappetizing trait that keeps the leaves free of insect damage and of such good visual quality throughout the growing season. In July, the trees become a beacon for honeybees as myriad clusters of small white flowers open in profusion. These are followed by even showier, bright red seed capsules that age to black, splitting to reveal diminutive, shiny, dark brown seeds. Evodia is outstanding when in fruit; a lovely specimen near the Caldwell Road entrance to the arboretum never fails to draw laudatory comments in August and September.
Another sparely branched, round-headed, small tree is the golden rain tree. One of the few winter hardy-members of the soapberry family (Sapindaceae), most of whose members are tropical, this one is native to China, Japan, and Korea. However, Koelreuteria is still pushing the envelope here-in severe winters it may suffer some dieback, and usually never approaches the 35-foot heights it attains in warmer areas. Its glossy scalloped foliage is twice pinnately compound, each leaflet deeply lobed or divided, providing a nice dark backdrop for the triangular, 12-inch-long, upright clusters of rich yellow flowers in July. These flowers are followed by clusters of inflated translucent seed capsules, each shaped like a Japanese paper lantern, which gradually age from green to yellow and finally tan. For a slightly later bloom try 'Rose Lantern', which blooms in August; its young papery seed heads are tinged with pink. Koelreuteria is not fussy about soil and will grow nicely in shade, though it will be leggier and less floriferous. Golden rain tree is not seen much in this area, perhaps because of hardiness concerns or perhaps because few gardeners visit their local nurseries in the heat of midsummer when they could see this decorative tree in bloom.
Seven-son flower (Heptacodium miconioides) can be grown as a single-stemmed small tree, or a large, multi-stemmed shrub. A member of the honeysuckle family, it grows long shoots that with age become clothed with shaggy tan bark that exfoliates in long, slender strips. The attractive oval, slender-tipped foliage carries a curved impressed vein on either side of the midrib that makes the leaf center stand out. Although all these features are attractive, Heptacodium can easily be passed by during the spring and early summer when it blends demurely with the surrounding shades of green. Then, at the tail end of summer, when we are all anticipating the cooler days of autumn, billowy, loosely triangular heads of small fragrant white flowers open. The flowers are welcome at the dusty end of summer, but the striking, bright pink, persistent sepals that remain long after the white petals have fallen are really the star attraction. Heptacodium is a remarkably obliging plant that will grow almost anywhere, even tolerating poorly-drained clay soil, although with a slower growth rate than it would demonstrate in more fertile, well-drained soil. Here at Plantations, Heptacodium has been successful in several "problem" sites, where drainage is poor and soil pH is high, making it a good candidate for the clay soils so common in the Ithaca area.
These trees can be visited at Cornell Plantations, where Amelanchier abounds in the flowering shrub collection, and Koelreuteria rubs elbows with large viburnums in the F.R. Newman Arboretum; and where a magnificent Japanese snowbell in the rhododendron collection on Comstock Knoll spreads its horizontal branches beneath an overstory of white pine.
Mary Hirshfeld is director of horticulture at Cornell Plantations.