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 en have other ornamental features that make them deserving of a spot in your landscape.
Catalpa (Catalpa speciosa) has large showy white flowers in early to mid-June. Each flower has purple or yellow markings near the center or throat. Trees are large (over 50 feet) and hardy in USDA Hardiness Zones 4 to 8. Leaves are large, heart shaped and hairy. After flowering, long green pods form and mature to a brownish color (resembling skinny cigars), hence the common name cigar tree. Catalpa trees are adaptable and tolerant of diverse soil types, making them excellent choices for heavier, clay-type soils. Because they are fast-growing trees, they are often short-lived, however.
An Iowa native, the Pagoda Dogwood (Cornus alternifolia) is a small tree, maturing to 20-30 feet tall. It has a distinctly horizontal branching habit and is hardy in USDA Hardiness Zones 3 to 7. Flat-topped, creamy white flower clusters are produced in late May and are followed by dark purple, berry-like fruit in late summer. A woodland native, Pagoda dogwood performs best in partial shade. Plants prefer moist, well-drained, fertile soils.
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 (Heptacodium miconioides) 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.
An unexpected addition to this list is Linden (Tilia spp.). Linden is noted for its excellence as a shade tree – not showy flowers. However, some species and cultivars have distinctly fragrant flowers. Bees also love the flowers. Linden honey, made from the nectar of linden flowers, is a gourmet treat. Linden species are large trees, many reaching over 50 feet tall. Most species are hardy to zones . Plants require sunny sites, but are tolerant of diverse soil types.
Other summer blooming trees to consider are Stewartia (Stewartia spp.), Yellowhorn (Xanthocerus sorbifolium), Sweetbay (Magnolia), Tuliptree (Liriodendron tulipifera), Chinese Chestnut (Castanea), Sourwood (Oxydendrum arboreum), and Amur Maackia (Maackia amurensis). When considering any of the above mentioned species, research them carefully, as several are not reliably cold hardy in northern Iowa and all should be appropriately sited for best results.
Updated from an article that originally appeared in the July 16, 2019 issue of Horticulture and Home Pest News.