In the middle of January a blanket of deep crunchy snow covers Marjorie’s Garden. Everything lies buried except the tall spent stalks of a half dozen common mullein (Verbascum thapsus), rigid stems emerging from the sea of white like periscopes. Withered woody seed capsules, ravaged in autumn by a flock of goldfinches, still cling to the upper third of each stalk. Of the million or so tiny seeds produced by these plants, only a few escaped the birds and now lie scattered beneath the snow, waiting for light and warmth.
We don’t know the origin of the mullein plants in Marjorie’s Garden, but each May we cull most of the volunteer seedlings, tossing the small rosettes of gray-green fuzzy leaves on the compost pile. Along the edges of the garden’s beds we allow a few to grow through their first summer, hoping to see them flower the following year. Meanwhile, the previous year’s rosettes start to send up their stout flowering spikes.
A mullein plant in its second summer is a 6-foot-tall woolly mammoth. Densely hairy frost-green leaves clasp the lower two-thirds of the main stem, those nearest the ground more than a foot in length. The upper third of the stem develops into a stout spike of one-inch yellow flowers that open sequentially, bottom to top, over a period of several days.
A single mullein plant will produce hundreds of seed capsules, each bearing hundreds of seeds, for a total of around 200,000 seeds per plant, but only a small fraction will germinate and even fewer seedlings will make it to the second year. Mullein seedlings are not strong competitors, thriving only in the open margins of the garden and along the bed edges. In a typical summer we have a few flowering plants on the edge of the strawberry beds where they stand in strong contrast to the creeping berry plants, and a few selected first-year plants scattered around the vegetable and blueberry beds.
The flowers bring native bees and other pollinators to the garden; their late-summer seed heads bring goldfinches. On many summer mornings the edges of the large felted leaves are adorned with sparkling jewels, products of overnight guttation.
Recently I walked across the packed snow to take a closer look at this small colony of mullein stems. I broke away a few seed capsules, crushing them between my fingers in hopes of finding a few seeds overlooked by the finches, having read that the persistent winter fruits often do contain seeds. There were none, only a woody dust to pepper the snow.
Despite the deep snow, I could trace the garden’s bed lines from the position of the mullein stalks. Intolerant of shade and competition from other plants, only mullein seedlings that germinate on exposed bed edges are likely to survive into the second year. To hedge their bets, however, the seeds can remain viable in the soil seed bank for years, waiting for a disturbance to create an open space where they can grow.
Between my winter stroll among the mullein stalks and the writing of this essay, I struggled to reconcile cultivation in our garden of a non-native plant, a species that is considered invasive in some areas of the country. I did my homework, researching the invasive potential of mullein on the one hand, its possible role in the garden ecosystem on the other.
Common mullein is native to areas of Europe, northern Africa, and Asia. Imported to the United States in the 18th century, it was cultivated for medicinal uses and as a piscicide, its seeds used in the pre-Revolutionary War period to catch fish. It quickly became naturalized in open areas and, by 1818, was mistakenly considered native by Amos Eaton, a well known botanist of the time.
Mullein’s popularity in this country was enhanced by its use as a medicinal plant. To this day, an infusion of mullein flowers in olive oil is used as earache drops, its effectiveness attributed to strong antibacterial properties. Other products derived from mullein are used to relieve pain, treat allergies, and reduce inflammation. Anti-cancer and antioxidant properties have been attributed to certain mullein preparations.
Common mullein is not a native plant. But should it be considered invasive, capable of displacing native plants in relatively undisturbed areas? Its lack of tolerance for shade and a general intolerance for competition are factors that limit its capacity as a true invader. In addition, its seeds do not disperse very far from the parent plant, 75 percent falling within one meter of the parent, 93 percent within 5 meters. If you have common mullein in your garden, the seeds were likely introduced in purchased loam or in the soil of purchased plants rather than dispersed from plants in the area.
It seems unlikely to me that mullein has the potential to rapidly disperse into relatively undisturbed ecosystems. It is more likely to succeed only in open previously disturbed areas. In sections of the United States where it is listed as invasive, it appears to prevent establishment of native herbs and grasses following fires or other disturbances.
Is it possible for a non-native plant species, a benign intruder, to take on important roles in the garden ecosystem? As mentioned earlier, mullein seeds are a favorite food of goldfinches. Chipmunks also eat the seeds. Bumblebees and solitary native bees forage for nectar and pollen on mullein flowers. And native bees of the genus Anthidium
, including bees commonly called “mason bees”, “leaf-cutter bees”, and “carder bees”, use the hairs that coat the mullein leaves and stems in making their nests. Using her legs, the female carder bee scrapes (or “cards”, as with wool) the fine hairs from the leaf, then bundles the hairs into a ball that can be carried beneath her body back to the nest, typically a hollow reed or nest box cavity.
Common mullein has had over 200 years to insert itself into the local flora, to become a naturalized species and, when found in the garden, to function as part of the garden ecosystem. I’m sleeping well enough these days, untroubled by welcoming a non-native biennial into the garden. I’m looking forward to summer and those tall spikes of bright yellow flowers.