"Spring often gets all the attention when it comes to flowers, especially flowering trees. Yet, there are several tree species that bloom in early to late summer. In addition to their late bloom, these trees have other ornamental features that make them deserving of a spot in your landscape," writes Cindy Haynes, Iowa State University Department of Horticulture in an article on Summer blooming trees.
She lists some great choices from Catalpa to Xanthocerus. Here are some of her suggestions:
"Smokebush and Smoketree (Cotinus spp.) have fuzzy, delicate flowers and stems that resemble puffs of smoke when the plants are blooming. Blooms start in late May or June and often last for several weeks. Smoketree (Cotinus obovatus) has green leaves, reaches about 30 feet tall and is hardy to zones. Smokebush (Cotinus atropurpurea) has purple to burgundy leaves, usually matures around 20 feet tall, and is hardy to zones. Plants prefer sun to partial shade and well-drained fertile soils.
"There are several species of Hawthorn (Crataegus spp.) that bloom in May or June. The clusters of tiny, white, rose-like flowers are scented (usually not considered an enjoyable fragrance). After flowering, small red berries decorate trees in late summer and fall. Some species have thorny stems. Plants range in height from 30 to 50 feet and are hardy to at least zone 4. Plants are adaptable to a wide range of soils and site conditions.
"Seven Sons Flower (Hepatacodium micronoides) is one of the latest blooming trees. It is loaded with clusters of white flowers in late August and into September. The fragrant flowers are a favorite of bees, butterflies, wasps, and other pollinators. After flowering the sepals turn rosy pink and remain attractive through September or early October. Plants reach 20-30 feet tall and are hardy in USDA Hardiness Zones 5 to 9. In winter these small trees are noted for their attractive, exfoliating, tan bark.
"Golden Raintree (Koelruetaria paniculata) produces 12 to 15-inch-long panicles of bright yellow flowers in June or early July. The flowers develop into papery fruits (capsules) which resemble Chinese lanterns. The fruits change from green to yellow to brown. Leaves are large, pinnately compound and dark green. Plants grow 30-40 feet tall. The golden raintree is best suited to southern Iowa. It is not reliably cold hardy in northern portions of the state. Trees prefer sunny sites with well-drained soils.
"Another June bloomer is Japanese Tree Lilac (Syringa reticulata). Japanese tree lilac has large, fragrant, creamy white flower clusters on plants that reach 20-30 feet tall. The fragrance of the flowers is privet-like. It is one of the hardiest trees on the list, as trees are hardy to zone 3. Trees are also noted for their smooth, dark cinnamon colored bark."
Those are but a few on her list. You'll enjoy reading about other Summer blooming trees, and maybe decide to plant some in your own landscape.
Credit goes to Cindy Haynes, Horticulture and Home Pest News, and Iowa State University Extension and Outreach.