Trees that flower in May help home landscapes transition from early spring's short and often chilly days to the warm, lingering daylight hours of June and full summer. Many of these trees follow their May blossoms with edible summer or fall fruit. Even those that don't, however, bring color and fragrance during their blooming periods, and cooling summer shade when their flowers are gone.
Southern catalpa tree (Catalpa bignonioides) grows wild along riverbanks and streams from Georgia and the Florida Panhandle, west to Alabama and Mississippi. Standing between 30 and 40 feet high and up to 40 feet wide, it's hardy to minus 20 degrees Fahrenheit. Large, round or heart-shaped leaves are pale green. In May, according to the Missouri Botanical Garden, southern catalpa has upright spikes of exceptionally fragrant, bell-shaped white flowers. Purple and yellow throat blotches increase their showiness. Cigar-shaped brown seedpods follow.
This generally pest-and-disease-resistant tree may suffer from mildew, twig blight, leaf spots or damage from the catalpa sphinx moth caterpillar. It also attracts aphids, whiteflies, scale and mealybugs. While it tolerates poor soils, it does best in a well-drained, moist-to-wet loam.
Fringe tree (Chionanthus virginicus) is a small--12 to 35 feet tall and wide--native to the eastern United States. Tolerating winter temperatures as low as minus 40 degrees Fahrenheit, it grows on rocky bluffs, moist banks and infertile woods. Large, spear-like leaves bring yellow fall color. In May, its branches have hanging 4-to-6-inch clusters of fragrant, white, fringe-petaled flowers. Birds and wildlife feed on the pollinated female trees' blue-black fruit.
Grow fringe tree, advises the Missouri Botanical Garden, as a lawn specimen, in woodland or shrub borders, along stream banks and ponds, or in native plant gardens. Position so its spectacular May bloom is well-displayed. Give it full sun to partial shade and moist, rich soil. Tolerant of urban pollution, it suffers in prolonged drought.
Violet willow (Salix daphnoides) is a 7-to-20-foot tall tree native from Europe to central Asia and into the Himalayas. Hardy to minus 40 degrees Fahrenheit, it also grows as a 15-foot wide shrub. From early fall into midwinter, its stems take on an appealing shade of violet, says the Missouri Botanical Garden. Between April and May, it has ornamental pale gray catkins. Dark green, toothed, oblong leaves follow the blooms.
Vulnerable to numerous leaf diseases, this tree also attracts aphids, borers and scale. Even so, it's a good choice for erosion control in wet areas. Use it in low spots where water collects, or along streams and pond banks. It does best in full sun and moist, well-drained average soil.