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Swamp rose mallow (Hibiscus moscheutos)

What's in Bloom: September

Welcome to the September issue of the What’s in Bloom blog at the Morris Arboretum! Recent heavy rain storms have been a welcomed end to this summer’s drought, and although the peak flowering season has passed, there are still lots of beautiful blooms to appreciate in our gardens. A number of the plants highlighted this month are located in the Arboretum’s natural areas, meadows, and wetlands, teeming with life and color as we ease out of summer and into fall. From large white hibiscus flowers to the tiny flowers of a single grass spikelet, there is still so much to enjoy and look forward to this coming season.


Solidago canadensis
Solidago gigantea

The meadows at the Arboretum are bearing a bright, warm yellow hue as native goldenrod blooms. Small flower clusters arranged in a pyramidal shape crown these six-foot-tall stalks. A member of the Aster family, goldenrod blooms consist of many tiny flowers—what appears to be one flower emerging out of a bud are actually a number of small florets. S. canadensis and S. gigantea are two of the goldenrod species currently in bloom. Try to find both of these in the meadows: S. canadensis has hairy leaves and stem, while S. gigantea is smooth.

New York ironweed
Vernonia noveboracensis

Among the goldenrod in the meadows is this other beautiful native wildflower, its wide-spreading larger purple flowers complementing the tiny upright yellow blooms of the goldenrods. Another member of the Aster family, ironweed has similar flower structure to goldenrod, with each purple bloom consisting of many small florets.

Wood grass
Sorghastrum nutans

A more inconspicuous bloom hidden in the bold colors of the meadows are the flowers from this native warm-season grass. Growing up to five feet tall, wood grass is a staple of the vast prairies that once covered central North America. The flowering stalk is topped with light brown spikelets in a feathery branched arrangement known as a panicle. Emerging from each spikelet are two white stigmas and several bright yellow anthers which collect and produce pollen, respectively. There are several other grass species currently blooming in the meadows, each with varying spikelet arrangement and color. Switchgrass (Panicum virgatum), for example, has a wider panicle with green spikelets bearing purple stigmas and orange anthers.

Swamp rose mallow
Hibiscus moscheutos

Visible from the main entrance drive, the large white blooms of this native hibiscus dot the Arboretum’s wetland at this time of year. Look inside, and you’ll notice that each flower has a dark crimson center. Although swamp rose mallow blooms are only open a couple days, each plant will open new flowers until early fall, attracting lots of valuable pollinators to the wetland.

Aconitum sinomontanum

Native to China, this plant bears unique flowers as we near the end of summer. Walking along the path from the Widener Visitor Center to Out on a Limb, you’ll notice clusters of small purple flowers brightening this shady area of the garden. Each flower has a distinctive cupped upper petal known as a galea, which in Latin directly translates to “helmet.” Another name for monkshood is wolfsbane—members of the genus Aconitum contain the toxin aconitine, which may have historically been used to poison wolves.

Bougainvillea golden-rain-tree
Koelreuteria bipinnata

Tucked behind the parking lot by the top of the Orange Balustrade, this tree is a bright pop of color in the gardens this month. Branched clusters of small yellow flowers decorate these wide-spreading trees, whose delicate flower petals will soon fall and leave a carpet of yellow on the ground, hence the name golden-rain-tree. If you can, observe the individual flowers and notice their lovely fragrance and distinctive red color at the base of each petal.

Spider flower
Cleome spp.

This fun flower gets its name from its many long, spindly stamens (male reproductive organs) that shoot out from each inflorescence. Located throughout the Rose Garden, these tall, brightly-colored flowers beautifully complement the roses that are still blooming—they even have little prickles along their stems! These plants will continue to bloom until it frosts, adding consistent visual interest to the gardens long after peak blooming season is over.

Nora Wildberg received her bachelor’s degree in Art and Archaeology from Princeton University in 2021, focusing her studies on museology. Having previously worked with an ancient coin collection, she now works directly with the Morris Arboretum’s living collection assisting in the preservation and record-keeping of our woody plants. In recent years, she developed a passion for plants and nature, and in her free time, she enjoys birdwatching, painting, hiking, and looking at art.