Summer-flowering trees, like fall-blooming bulbs and spring-blooming asters, receive short shrift, simply because they blossom at an unconventional time. Just as we expect crocuses in March (and don't quite know what to make of them in October), so we equate flowering trees with crab apples, dogwoods, red-buds, and cherries. That's what we see when we plunder the garden center in April, and when we ogle the almost rococo excesses of spring in full plumage.
What we forget in our vernal rapture are the many trees that flower long after the spring divas have flounced off the stage. Trees that make their biggest splash when the yard is in greatest use and color is at a premium. Trees that can rekindle a planting that flags after spring or anchor one that climaxes in summer. Trees that deserve our consideration even when spring has us enthralled.
Among the first trees to greet summer with its flowers is Japanese tree lilac (Syringa reticulata), whose linen-white feather-duster flower heads—suggestive of a drift of puffy late-June clouds—debut in Midwestern and Northeastern gardens during the final days of spring. The flowers carry a dense, sweet, slightly musky perfume, which most noses (but not all) find agreeable. Variable in habit, flower, and foliage (several selections are in circulation), it forms a low-branching tree or multistemmed shrub up to 30 feet in height. In all its manifestations it possesses a hardy constitution (almost any sunny, not-too-damp site in USDA Zones 3 to 7 will do) and attractive hazelnut-brown bark, reminiscent of cherry. Its close relative (sometimes listed as a subspecies) Peking lilac (S. pekinensis) is similar in attributes and cultural requirements.
With July come the blooms of another rock-hardy (to Zone 3) northeast-Asian native, Amur maackia (Maackia amurensis). Although its dense five-inch spires of bone-white pea flowers are hardly spectacular, they nevertheless make a pleasing display when few other trees are in bloom. Its neat rounded compact habit, dainty deep-green leaves, and polished bronzy bark recommend Amur maackia as an all-season tree for sunny lawns or patios. Also worth hunting down is Chinese maackia (M. chinensis), remarkable for its shimmering, silky silver-gray spring foliage.
Combine the rippling smooth gray bark of a beech, the lush and lustrous pinnate leaves of the handsomest ash, abundant flat-topped clusters of fragrant white flowers followed by conspicuous red fruits, and adaptability to almost any soil in sun or light shade, and you surely have the makings of a tree destined for stardom. Yet its late-July to August bloom time and its less-than-euphonious, taxonomically muddled botanical name (Tetradium daniellii, Evodia daniellii, or Euodia daniellii, take your pick) have sentenced the beebee tree to undeserved obscurity. Relatively rapid in growth and moderate in size (with upright, spreading branches achieving 30 to 40 feet in height and breadth), it makes a superior specimen for small or middling yards within its wide hardiness range (Zones 5 to 9).
With its billowing swarm of lavishly borne sunny yellow flowers, a golden rain tree (Koelreuteria paniculata) in full bloom is the embodiment of midsummer. Symmetrically rounded and open-branched in habit (reaching some 30 feet high and wide), handsome in leaf, and ornamented in fall and winter by tan lanternesque seedpods, it more than holds its own at all seasons. Later-flowering selections (such as ‘September’) occasionally appear in catalogs, as does a somewhat outlandish and afloriferous bean pole form (‘Fastigiata’). Southern and Pacific Coast gardeners can also delight in the bougainvillea flame tree (Koelreuteria bipinnata), which is similar in characteristics and needs (sun and any reasonable soil), but less cold hardy (to Zone 7 rather than Zone 5).
Flowering at much the same season as golden rain tree, Japanese stewartia (Stewartia pseudocamellia) is a plant of more subtle—but equally seductive—charms. Rather than bearing bucketfuls of individually unremarkable flowers, it offers a celestial scattering of up-facing camellia-like blooms whose ruffled white petals and bristling orange-yellow stamens beg close inspection. In autumn, the finely toothed oblong leaves—which are untroubled by pests—assume brilliant shades of gold, orange, and crimson purple. And whatever the season, the bark of a mature specimen, with mottlings of cinnamon and cream and silver gray and numerous other earthy tones, is a thing of beauty, and an excellent argument for growing Japanese stewartia as a multistemmed tree rather than as a standard—the more bark, the better. Korean stewartia (Stewartia koreana) possesses the same virtues on a somewhat larger scale, and like Japanese stewartia has given rise to several worthy cultivars (including ‘Korean Splendor’ and ‘Ballet’) that are becoming increasingly available. Gardeners in Zone 6 and southward who seek a choice small tree or large shrub for partial shade should put all of the above at the top of their list.
White camellia-like flowers and showy fall color are also among the ornamental blandishments of Franklin tree (Franklinia alatamaha), which blooms somewhat later than Japanese stewartia (with flowers and autumn color sometimes overlapping in the northern districts of its Zones 5b to 9 hardiness range). Although the bark of its multiple stems cannot rival that of the stewartias, it does develop attractive, silvery striations with age, giving considerable winter interest. These ornamental attributes are doubtless what caught the attention of the eighteenth-century American plantsman William Bartram, who happened upon (and took cuttings of) Franklin tree while plant-hunting along Georgia's Altamaha River in 1765. Franklinia mysteriously disappeared from the wild within the next few decades, and is now known only in gardens, where, with sun, a humus-rich soil, and a little luck (it can be a temperamental thing), it makes an outstanding specimen tree or large shrub, as well as a surefire conversation piece.
A Southeast native that, happily, hasn't gone the way of Franklin tree, sourwood (Oxydendrum arboreum) is one of those rare plants that seem to animate the landscape, its bowing branches and cascading, frothy sprays of arching white lily-of-the-valley inflorescences suggesting motion (poetry in motion, in this case). The July and August flowers morph into conspicuous ivory seed capsules, which combine with sourwood's glossy deep green late-summer leaves and spectacular fall color (think gold and dazzling scarlet and burgundy) to produce a further show. Factor in its attractive alligator-hide bark, and you've got one of the best small native (or otherwise) trees for any Zone 5 to 9 garden that can supply it with the acid soil and part- to full-day sun it requires.