It’s said, in the Midwest, where I was raised, that you can stand in the middle of a cornfield on a summer day, close your eyes, and hear the stalks and leaves expanding. At the Arboretum, the growth is seemingly silent, but still, the plants are racing headlong into summer, with lanky shoots that, in some cases, are already bending with fruit. If you walk into the collection and close your eyes, however, the world still purrs with life: the squawking and warbling of birds, the conspicuous rustling of a garter snake (Thamnophis sirtalis) wending through the undergrowth, and even the drone of distant construction equipment or an overheard phone greeting to “the love of my life.” Yet, if you are standing in the right place, you will hear what seem to be the loudest workers of all—or at least, the loudest given their size. I’m talking about bees—particularly our native bumblebees (Bombus spp.).
On a recent morning, on Bussey Hill, one of these bumblebee hotspots was a species of Chinese hydrangea (Hydrangea longipes, accessions 639-2010 and 640-2010), positioned in two groupings within the Explorers Garden. The first, not far from the Franklin tree (Franklinia alatamaha, accession 2428-3*A), grows in a shaded location, where the white flowers on two of the three plants pop from the shadows. This is the first year the species has flowered at the Arboretum, and the bumblebees seemingly cannot get enough. The flowers form a broad flat surface for the bees to nose across, with showier sterile flowers around the periphery. But if those first plants seem busy, the second planting, located closer to the stand of seven-son flower (Heptacodium miconioides, accession 425-91), are complete chaos. These three hydrangeas grow in a more open location, with trees around sidelines but nothing directly overhead. This year, the plants are covered with flowers, and the flowers, in turn, are literally overrun with bumblebees, as loud and raucous as an elementary school cafeteria on the last day of class, before summer vacation—a genuine free-for-all.
Yet, the bumblebees do not collect pollen for themselves, or at least not entirely. Perhaps the flowers would be more accurately likened to a grocery store—specifically a grocery store the afternoon before the Fourth of July, when everyone is mad-dashing for relish and hotdogs (or “notdogs”). On closer examination, I noticed that the bumblebees held yellow globules of pollen on their hind legs, and this pollen would soon be carried home to feed their larvae. Callin Switzer, a Harvard doctoral graduate, conducted research on bumblebees at the Arboretum, documenting how the bees change the frequency of their buzzing to dislodge pollen—a technique known as buzz pollination. While some plant species require buzz pollination (including garden crops like tomatoes, Solanum lycopersicum), hydrangeas are freer with their pollen, and myriad smaller, non-buzzing insects were also exploring the flowers. Beneath all this commotion, the rough hydrangea foliage stretches broad and long, and many served as bibs for the foraging frenzy above, catching a littering of small petals and dried stamens.
All six of the plants were collected on the same North America-China Plant Exploration Consortium (NACPEC) expedition to Shaanxi Province, China, in 2010—a landlocked province located northeast of Sichuan. The Arboretum’s Michael Dosmann collected the seed with Tony Aiello, of the Morris Arboretum, and Kang Wang, from the Beijing Botanical Garden. They observed hydrangea populations at two distinct locations within Hong He Gu Forest Park, a mountainous preserve in the south-central portion of the province, where the plants rarely exceeded three feet in height, much like their progeny at the Arboretum. Interestingly, the Arboretum has attempted to cultivate this species with seven earlier accessions, from which only three plants migrated to the grounds. The most recent attempt—before the 2010 collection—came from a 2008 NACPEC expedition that visited this exact same park, but those seeds were collected at elevations between 460 and 630 meters lower (approximately 1,500 and 2,000 feet). Two of the resulting plants were positioned in the Explorers Garden, where both died from winter temperatures. It’s tempting to suspect that the 2010 collections, from higher elevations, were ever-so-much hardier.
In the expedition collecting report, Michael noted that some of the hydrangeas were growing in dense shade, others in the open. “It would be nice to observe this species in a cultivated setting and see just how wide a range of sunlight it can grow in—and thrive.” As it ended up, the six plants were positioned in two discrete locations within the Explorers Garden—one in shade, the other in sun (or part-sun)—and this year, with the plants putting on an impressive show, the bumblebees seem to confirm that both plantings are living up to the plant collectors’ dream: they’re thriving at last.