The other day I was describing to Heather Holm a “garden nocturne” I once planted, a collection of night-blooming flowers such as flowering tobacco and moonflower that I clustered around a small patio. I used to sit on that patio with a glass of wine at dusk to watch the blossoms open. Heather, who has written two fine books about the pollinators of native plants, impressed me by suggesting correctly that all those flowers had been white or cream-colored and that their perfumes had been penetrating. She knew this because she knew that the pollinators of these night-blooming plants are moths, and these are characteristics that attract moths. In fact, I admitted that the hummingbird-like sphinx moths that used to hover around the open blossoms of my nocturne were one of its chief attractions.
I was talking to Heather because I wanted information about the myriad of insects besides bees that pollinate our plants. Pollination is integral to the production of fertile seeds; pollen from the male parts of a flower must be moved to the female parts to fertilize them, and in many types of plants this involves carrying the pollen from one flower to another. Honeybees, although not native to North America, are, of course, the charismatic pollinators, the ones that everyone immediately thinks of when the subject of plant and crop pollination comes up. However, Heather was quick to add that our native bees, her special enthusiasm, play a decisive role in the pollination of native plant species as well as providing important services on the farm. But then there are all the other insects that contribute to this process, pollinators that the average gardener may not know about.
Who would have thought, for example, that flies play a significant role in flower pollination? Yet, hoverflies are second only to bees in their importance as pollinators. They are called hoverflies because they are frequently seen hovering around flowers, especially flowers in the carrot family, which includes many familiar garden plants such as parsley, parsnips, celery, chervil, coriander, caraway, cumin, dill and fennel. These all bear their flowers in umbrella-like clusters, and the individual blossoms tend to be small and shallow, which suits the hoverflies, whose mouth parts are short and not good for probing deep into tubular blossoms for the pollen or nectar on which they feed. You may not have noticed hoverflies because of a peculiar fact. Although stingless, many of them mimic bees or wasps in appearance, which deters the predators that might otherwise feed on them. Hoverfly larvae also have an important role to play in the garden. Some of them are insectivores and feed on aphids, thrips and other sap-sucking plant pests. This is why organic gardeners often advise including plants of the carrot family in your garden to attract hoverflies and enhance natural pest control.
According to Heather, tubular blossoms—such as those of our native phloxes—demand longer-tongued pollinators, and these are chiefly serviced by butterflies and moths. Other tubular flowers—especially those that are red, a color most insects cannot see—depend on hummingbirds. These long-tongued pollinators are typically less effective than bees, who collect pollen deliberately and whose hairy bodies are very effective in moving it from plant to plant. Butterflies and moths, in contrast, move only the pollen grains that inadvertently stick to their nectar-seeking tongues. Their relationship to the flowers as pollinators is, as Heather puts it, “rather precarious.”
Wasps, beetles and even ants all play a role in flower pollination, too. I asked Heather what we can do to encourage these essential visitors. She replied that when it comes to gardening, her mantra is “less is more.” That is, the less you disturb the habitat of the garden by tidying up, the more insects and pollinators it will host. She herself lets fallen leaves remain mostly where they land and restricts her garden clean-up to cutting back the dead flower stalks in spring. Traditionalists will likely want a tidier garden than this, but even they should consider leaving some patches wilder to serve as preserves for pollinator populations.
If readers want to listen to the rest of my conversation about pollinators with Heather Holm, I suggest they log onto my website thomaschristophergardens/podcast, or go to Berkshire Botanical Garden’s website, berkshirebotanical.org, and click first on “Learn” and then on “Virtual Learning.” There, you can learn more about the curious insects that pollinate our flowers, as well as find information about Heather Holm’s books.
Be-a-Better-Gardener is a community service of Berkshire Botanical Garden, located in Stockbridge, Mass. Its mission, to provide knowledge of gardening and the environment through a diverse range of classes and programs, informs and inspires thousands of students and visitors each year. Thomas Christopher is a volunteer at Berkshire Botanical Garden and is the author or co-author of more than a dozen books, including Nature into Art and The Gardens of Wave Hill (Timber Press, 2019). Be-a-Better Gardener is syndicated in 19 print and online publications, reaching 250,000 readers. Tom’s companion broadcast to this column, Growing Greener, streams on WESUFM.org, Pacifica Radio and NPR and is available at his website, https://www.thomaschristophergardens.com/podcast.