Native Milkweed and Bellflower Sustain the Garden’s Bumblebees

Posted Aug. 06, 2010, at 7:04 p.m.

Every morning for the past week you could find me in the garden tickling blueberries for breakfast. Marjorie taught me the tickling method, the best way of harvesting each highbush blueberry at the peak of its sweetness.

I cup my hand around a cluster of berries, only some of which are fully ripe, and wiggle my fingers. The berries ready to slip their connection with pedicel will do so; the others will be there tomorrow.

As I tickle berries, I think about the bumblebees that pollinated blueberry flowers earlier in summer. I watched them move from one white bell-shaped blossom to another, and I thanked them in advance for the coming harvest.

Now, when I hear familiar buzzing in a nearby bed, I stop tickling berries long enough to watch bumblebees pollinate blossoms of sunflower, 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 bright yellow pollen, and 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 (“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 the squash and tomatoes.

One way a gardener can thank the bumblebees is to help them build strong colonies within or near the garden by providing an abundance of blossoms for them to forage from early spring into fall. Native herbaceous perennials that flower in July and August, including goldenrods, milkweeds and campanulas, will help sustain bumblebee colonies as vegetable flowers fade.

Campanula rotundifolia

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.

Asclepias tuberosa

Although Asclepias tuberosa, 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 3 to 4 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 seedpods (4 inches long) which split open at maturity releasing silky-haired seeds on the wind.

In addition to bumblebees, butterflies use swamp milkweed as a nectar source while the foliage is a food source for monarch butterfly larvae.

You can get up close and personal with these two native species, as well as the bumblebees that rely on them, at the native plant garden that surrounds the University of Maine Cooperative Extension office building for Hancock County, located in Ellsworth (see http://extension.umaine.edu/hancock/ for directions). While there you can also see large clumps of Joe-Pye weed (Eupatorium purpureum) swarming with bees, three species of native goldenrod (Solidago sp.) just starting to flower, a tall sunflower (Helianthus giganteus) ideal for garden wet spots, and several native shrub species that attract birds and pollinators. All of the plants are carefully labeled.

While you are in your garden, look for bumblebees hard at work pollinating tomato blooms. Stop and watch this unique activity, and say thank you for the tomatoes.

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