In the vegetable garden at harvest time, when I hear familiar buzzing in a nearby bed, I stop tickling blueberries long enough to watch bumblebees pollinate the flowers of summer squash and tomato. Unlike a honeybee, which prefers to forage in a large field of a single plant species, a bumblebee will move from one type of plant to another. It might start with a sunflower head, crawling over each tiny flower until it has filled its hairy hind-leg sacs with bright orange pollen, then dive into the throat of a male squash blossom, dusting its bristly body with yellow pollen, and then move on to a cluster of tomato flowers, grasping each blossom in turn with its legs and vibrating wing muscles at just the right frequency to release the pollen, a process called sonication or “buzz pollination” that is unique to bumblebees and essential to maximum tomato production.
I take a break from harvesting blueberries to watch bumblebees make their rounds, and I thank them for squash and tomatoes.
One way a gardener can thank the bumblebees and other native pollinators is to help them build strong colonies within or near the vegetable garden by providing an abundance of blossoms for them to forage from early spring into fall. Many herbaceous perennials that flower in July, including goldenrods, milkweeds, and campanulas, will help sustain pollinator colonies.
Catmint (Nepeta x faassenii)
One of my favorite garden spots in July is the perennial bed in the heart of Marjorie’s Garden. In a corner of this bed, where the deep purple flower spikes of catmint meet and mingle with the chartreuse flowers of lady’s mantle (Alchemilla mollis), bumblebees dance from dawn to dusk throughout the month, the tall slender catmint spikes swaying under the weight of these tireless pollinators. Often in early morning I find a bumblebee asleep, or so it seems, having spent the night on a catmint flower, too tired at dark to carry its heavy load back to the nest. Warmed by a fleck of sunlight, it awakens while I watch and resumes foraging.
Catmint is easy to grow, thriving in lean, dry soils with little care. We fertilize ours with topdressings of composted manure in early spring, before growth begins, taking care not to cover the plants themselves. In late summer, when the plants have finished blooming, we shear them back to rejuvenate the foliage and keep them tidy.
Penstemons (Penstemon sp.)
In July, somewhere in the dry woods and rocky hillsides of Penobscot County, Maine, the rare hairy beardtongue (P. hirsutus) blooms. At the same time and nearly statewide (excepting Piscataquis and Washington Counties), the uncommon foxglove penstemon (P. digitalis) flowers in fields and woodland borders. And while I’ve done my share of botanizing where these herbaceous perennials grow, I’ve missed them, perhaps spending too much time looking up into the canopies of trees instead of down on the ground.
I know penstemons from gardens. Both species thrive in full sun at the University of Maine Cooperative Extension native plant garden in Ellsworth, and a cultivar of the foxglove penstemon with maroon-colored leaves, Husker Red, grows in Marjorie’s Garden to the delight of ruby-throated hummingbirds.
The hairy beardtongue is a woolly-stemmed plant growing 16- to 24-inches tall with open, stalked clusters of lavender trumpet-shaped flowers, each about one inch long with a white tip. The foxglove penstemon is taller, growing from 3 to 5 feet in height with a spread of 2 feet. Its flowers are white, slightly longer than those of hairy beardtongue, and are borne in panicles atop erect, rigid stems. Both species have a clump-forming growth habit.
Best in full sun, penstemons will tolerate partial shade. They need well-drained soils and can tolerate periods of moderate drought.
More common in garden centers than in the wild, our native penstemons are ideal candidates for the pollinator garden. Both attract hummingbirds as well as bumblebees and butterflies. The hairy penstemon is a documented host for the Baltimore Checkerspot Butterfly, a species found throughout New England.
Beneficial insects like ladybird beetles, whose larvae feed on aphids and other garden herbivores, require a source of pollen and nectar as adults. Native penstemons provide these essential foods.
Campanulas (Campanula sp.)
Campanula rotundifolia, the bluebell bellflower, blooms continuously from late spring through August. Native to dry, nutrient-poor grasslands in Maine and throughout much of the United States, this rhizomatous perennial produces violet blue, bell-shaped flowers in loose clusters on long, thin, graceful stems. It performs best in sandy, well-drained soils, sun to part shade, and is perfect for the pollinator garden, attracting hummingbirds as well as bumblebees.
In order to reach the nectar at the base of the blossom, the bumblebee must crawl into the bell, disappearing except for the tip of its butt. It is not surprising that by the end of the flowering season the entire plant is bent over from the weight of bees.
The peach-leaved bellflower or willow bell (Campanula persicifolia), native to Europe, Northern Africa, and parts of Asia, grows to 3 feet tall with sturdy flowering stems arising from a rosette of bright green leaves. The large bell-shaped flowers, ranging from white to a deep lavender-blue, first appear at the end of June. Plants reach their peak of flowering in July but will continue to bloom into August if spent flowering stalks are removed.
Willow bell is easily grown in average, medium moisture, well-drained soils in full sun to part shade. It prefers New England’s cool summers.
Swamp milkweed (Asclepias incarnata)
Although swamp milkweed is native to swamps and wet meadows in most of the continental U.S., including Maine, it is surprisingly tolerant of average well-drained soils in cultivation. Blooming in July and August, this erect, clump-forming herbaceous perennial grows three to four feet tall. It has a deep taproot and is best left undisturbed once established.
Swamp milkweed’s flowers, ranging in color from pink to mauve, occur in tight clusters. The flowers are followed by four-inch-long seed pods which split open at maturity releasing silky-haired seeds on the wind.
If you are planning to grow milkweeds to attract monarch butterflies, the swamp milkweed is one of the best species for most gardens, its compact habit much preferred over the aggressive rhizomatous growth habit of the common milkweed, A. syriaca. This later species should only be grown where there is sufficient room for its rampant colonizing habit.