Summer Shrub Flower Power
Butterfly bush (Buddleja davidii) cultivars used to be the go-to shrub for large masses of long-blooming color, attractiveness to butterflies, and easy care during the hottest, driest days of summer. But with its invasive tendencies now writ large upon the landscape in many places, including parts of Pennsylvania, the gardener may want to consider other plants to fill the spaces once occupied by butterfly bush.
The good news is that there are quite a few bushes to select from that provide abundant blooms and excellent pollinator pasture during the mid to late summer months of July, August, and September. In this article, I have included a dozen outstanding summer shrubs with flower power, all hardy throughout Pennsylvania, some native to the eastern United States, and some non-native shrubs that, so far, have not exhibited the invasive potential of butterfly bush.
First, consider six eastern U.S. native shrubs: bottlebrush buckeye, New Jersey tea, buttonbush, summersweet, Northern and Southern bush-honeysuckle, and steeplebush.
Bottlebrush buckeye (Aesculus parviflora) forms a suckering mound with tiered branches; it can reach 8 to 12 feet in height and 8 to 15 feet or more in spread. It prefers moist, well-drained soil, in sun to light shade, and is fairly drought tolerant once established. The individual flowers, white with long thread-like pinkish stamens, are arranged in 12-inch panicles that look like bottlebrushes and bloom for most of July, attracting hordes of butterflies, in particular, tiger swallowtails and spotted skippers. The palmately compound leaves are resistant to summer scorch and will develop a beautiful yellow fall color if the plant has sufficient moisture and light.
New Jersey tea (Ceanothus americanus) is of compact stature, about 3 feet in height and width, but a powerhouse nectar source for many kinds of insects as well as a larval host plant for numerous butterflies; William Cullina considers it “among the top 10 native shrubs for butterfly gardens.” It prefers sun to part sun and well-drained, acidic soil and tolerates heat and drought conditions. Numerous small white flowers appear in mid-summer, clustered at the top of stems clothed in simple, dark green leaves.
Buttonbush (Cephalanthus occidentalis) is a larger shrub for sun to light shade, from 6 to 8 feet in height, with a definite preference for moist to wet soils; it does not perform well in dry soil. Glossy dark-green leaves set off the 1-inch globes of creamy white tubular flowers that look like little round pincushions and offer abundant nectar to butterflies such as tiger swallowtails and fritillaries. Because it blooms on new wood each season, it can be cut back in late winter for a more compact, rounded form of 3 to 4 feet.
Summersweet (Clethra alnifolia) is a compact shrub well suited to smaller gardens; it ranges from 4 to 8 feet in height and width, depending on the cultivar, of which there are many. Also called clethra or sweet pepperbush, it forms a rounded, dense mass of dark, glossy green foliage, topped in July and August with 4-inch candles of small, delightfully fragrant, white or pink flowers that are adored by pollinating insects. Clethra grows in sun to light shade and prefers moist to wet soil, although it will tolerate average soils if it does not get too hot or dry. In the fall, the foliage turns golden yellow as the interesting seed capsules ripen to brown. It spreads by suckers to form colonies, but it can be cut back in spring if it gets too scraggly, as it blooms on the growth of the current season.
Northern and Southern bush-honeysuckle (Diervilla lonicera and Diervilla sessilifolia) are two similar species, ranging in height and spread from 3 to 6 feet, that are well-suited to massing and very adaptable to moist to dry soils in sun to light shade. With small tubular yellow flowers forming in the axils of paired leaves near the tips of the reddish arching stems, bush-honeysuckle will attract butterflies over a long period during the summer. New foliage emerges with a coppery color that fades to a reddish hint as the leaves mature.
Steeplebush (Spiraea tomentosa) has pink to rose-purple fuzzy flowers in narrow, pointed spires that bloom in late summer on 2 to 5-foot stems, attracting a wide array of pollinating insects. It prefers sun to part sun and moist soils and looks its best in naturalized plantings or damp meadows. Because it is fast growing and blooms on new wood, it can be mowed or cut back seasonally.
Next, consider six shrubs that were introduced into the United States and appreciated in the garden for their form, flowers, and foliage: glossy abelia, blue mist shrub, seven-son flower, panicle hydrangea, crapemyrtle, and chaste tree. Although these shrubs are not host plants for native larvae, they provide late-summer food sources for many native insects. At present, none are included on the Pennsylvania DCNR's list of invasive plants.
Glossy abelia (Abelia x grandiflora) has abundant pinkish-white flowers from July through fall on a dense, rounded shrub, 3 to 6 feet in height and spread, with arching stems and glossy, semi-evergreen foliage. The late-season flowers attract hummingbirds as well as butterflies. It grows well in sun to part shade in moist, well-drained soil; there are now many cultivated varieties offering a range of foliage and flower colors.
Blue-mist shrub (Caryopteris x clandonensis), also called blue spirea or bluebeard, grows from 2 to 4 feet in height and width, with a mounded form, bluish-green aromatic foliage, and bright blue flowers borne in clusters along the upper stems that are a magnet for bees when they bloom from August into September. This is a great shrub for hot, dry situations in full sun and well-drained soil. It blooms on new wood each year; cutting it back in early spring is about the only maintenance it requires.
Seven-son flower (Heptacodium miconioides) is a large shrub or small tree, 15 to 20 feet high, with large, dark green leaves and stems clothed in attractive exfoliating bark. Small white fragrant flowers, arranged in an unusual 7-flowered whorl, entice bees and butterflies when they begin blooming in September and are followed by persistent rosy-purple sepals as beautiful as the flowers. This plant prefers rich, moist, well-drained soils in sun to light shade.
Panicle hydrangea (Hydrangea paniculata) has white to pinkish pyramidal clusters of small individual flowers, some sterile and some fertile, from July into September. Many cultivated varieties are available at garden centers, with an emphasis on those with more of the showier sterile flowers. But it is the smaller, less showy, fragrant, fertile flowers that offer nectar and pollen. 'Tardiva' is a cultivar of panicle hydrangea that has a mix of both fertile flowers for the bees and sterile flowers for our viewing pleasure. There are several species and numerous cultivars of "lacecap" hydrangeas that offer a greater proportion of the insect-enticing fertile flowers.
Crapemyrtle (Lagerstroemia indica) is a popular shrub that thrives in summer's heat and sun, with hundreds of cultivated varieties selected for size, growth habit, beautiful bark, and floriferous abundance in shades of white, pink, purple, and red. And, yes, the flowers offer nectar and pollen resources to bees. The University of Georgia researchers conducted a pollinator preference study in 2015 and 2016 and found that of the varieties observed, three cultivars, 'Seminole,' 'Victor,' and 'Apalachee,' were the most visited by various bees.
Chastetree (Vitex agnus-castus) also flourishes in full sun and hot weather. It has palmately compound foliage, with aromatic leaflets of bluish-green, and reaches a height and spread of 8 to 10 feet or more. Loose spikes of lilac-blue to deep blue flowers (depending on cultivar) bloom in July and August, providing excellent pasture for all manner of bees, butterflies, and pollinating insects. It blooms on new wood, so it can be cut back in early spring to control its size for the season.
