For the love of (wild) lupine

Driving through New England in June, you’ve probably come across waves of lupine lapping the roadside. Indigo flowers as far as the eye can see is hard to come by on the east coast, so it’s no wonder why New Englanders have an inordinate fondness for lupine. New Hampshire boasts about its must-see lupine through tourism campaigns, memorabilia, and open-air craft markets. In more than one state, entire celebrations are devoted to this existence of this plant. And both the real and fictitious Miss Rumphius sought to spread its violet steeples along the Maine coast. There’s only one issue: this beloved lupine is invasive.

A field of the invasive bigleaf lupine (Lupinus polyphyllus). Still, Miss Rumphius would be proud. PC: Rabbit Hill Inn.

Bigleaf lupine (Lupinus polyphyllus) is native to western North America but has colonized disturbed roadsides of New England as well as much of northern Europe. Even though, like all lupines, it enriches soils with nitrogen that could facilitate the growth of other plants, the opposite has been found; in areas where bigleaf lupine grows, it dominates. But that sea of flowers supports pollinators, right? Wild bees definitely take advantage of its pollen resources (its flowers lack nectar) while it flowers, but since a field of lupine often contains few other flowering plants, they will have to fly further to find food the rest of the year. Even more troubling is that no butterflies and moths in the east share an evolutionary history with bigleaf lupine, so their caterpillars cannot develop on its leaves. In places where bigleaf lupine is invasive, this ecological incompatibility has been found to reduce the local abundance and diversity of lepidopteran pollinators.

There is, however, a native lupine that plays an important role in supporting New England’s insect pollinators: wild lupine (Lupinus perennis). This equally (if not more, but maybe that’s just me) attractive lupine thrives in dry, sandy sites that are transitioning from grassland to forest. In New England, this often equates to powerline rights-of-ways or intentionally managed reserves. Bumble bees (Bombus spp.), carpenter bees (Xylocopa virginica), mason bees (Osmia spp.), leaf-cutter bees (Megachile spp.) are all capable pollinators, forcing themselves through the clamshell-like flowers to reach the reward (this lupine also doesn’t produce nectar). Notably, it is also supports three threatened butterflies in the region—karner blue (Lycaeides melissa samuelis), frosted elfin (Callophrys irus), and persius duskywing (Erynnis persius). Wild lupine is the sole food source for karner blue and persius duskywing caterpillars, and just one of two leguminous host plants of frosted elfin. Numerous other handsome Lepidoptera feed on its leaves during development including bella moth (Utetheisa bella) and phyllira tiger moth (Grammia phyllira).

Bumble bee foraging on wild lupine in Concord, NH. PC: Max McCarthy

Unfortunately, populations of wild lupine across its northern range have declined due to a combination of forest fire suppression, human development, and unbridled harvest. But don’t despair: there’s a deep-rooted interest in protecting wild lupine across its range at publicly accessibly locations. The USFWS Karner Blue Easement in Concord, NH boasts a small, but persistent population, and an impressive display can be viewed at Albany Pine Bush during their annual Lupine Fest in late-May. Across the border, High Park in Toronto is an excellent example of how fire-dependent plants (and ecosystems) can be managed alongside humans. If you visit either of the first two sites during summer, you’re might also spot karner blues dancing among the scrub. Remember that they are there only because wild lupine is there too.

Karner blue butterflies can develop on only one type of lupine: wild lupine. The common bigleaf lupine along roadsides does not support this endangered pollinator. PC: Justin Meissen, Flickr

I’m not proposing we launch a campaign to plant roadsides with wild lupine, nor am I saying that you should feel guilty about admiring the bigleaf lupine through your windshield. Rather, know the latter plays a mostly aesthetic role, whereas the former an ecological one. And if you want to directly help pollinators that depend on wild lupine? Buy sustainably sourced seed and plants for your garden and support organizations and initiatives (like the ones listed above) focused on restoring its ephemeral habitat to ensure it’s around for future generations and pollinators alike to enjoy.

To support spring pollinators, think big

In summer, pollinators are not often hard-pressed to find flowers. In fact, you might support them without even knowing it: community gardens, flowering herbs on front steps and balconies, or milkweed growing in a tree-well all provide food for pollinators during the hottest, longest days of the year.

But what about in spring? It’s not as easy to accidentally support pollinators during these cooler months of the year when the ground has just begun to thaw; there haven’t been that many warm days; and persistent rain (as continues this year) can impede pollinators from finding food. Indeed, queen bumble bees emerge from hibernation in early spring and need immediate access to both nectar and pollen in order to start their colonies for the year, and many solitary bees and hover flies are only active for several weeks in spring: no flowers means these pollinators cannot make it.

So, how can you support pollinators in April and May? Think big. Plant native flowering shrubs or trees. In New England, you’ll be hard-pressed to find better forage for insects than these woody plants. Not only do these larger plants produce copious amounts of flowers, but they are often important host plants for caterpillars of moths and butterflies. Plus, with the exception of woodland wildflowers, there simply aren’t enough growing days by mid-spring for most smaller, herbaceous (soft-stemmed) perennials to flower.

In addition to supporting pollinators, serviceberry produces delicious berries enjoyed by both birds and humans.
PC: Ryan Hodnett, Wikimedia Commons.

Choose plants that bloom sequentially from April through early-June. By selecting plants with overlapping flowering times, you will support a high diversity of pollinators regardless of when they emerge. To help you decide, here are several hardy options of native trees and shrubs that support bees, followed by average flowering times in Massachusetts:

  1. pussy willow (Salix discolor, early-April)
  2. red maple (Acer rubrum, early-April)
  3. eastern redbud (Cercis canadensis, late-April/early-May)
  4. serviceberry (Amelanchier sp., late-April)
  5. chokecherry (Prunus virginiana, May)
  6. red elderberry (Sambucus racemosa, May)
  7. nannyberry(Viburnum lentago, May)
  8. black cherry (Prunus serotina, late-May/early-June)
  9. red osier dogwood (Cornus sericea, May/early-June)
  10. ninebark (Physocarpus opulifolius, June)
The eastern carpenter bee (Xylocopa virginica) is one of the many native pollinators that enjoy redbud flowers.

Although many ornamental flowering trees are pretty, the frills that we enjoy often do little to help pollinators. Even worse, some ornamental cherry trees sometimes lack pollen and/or nectar altogether, making them essentially useless to flower visitors. In contrast, many ornamental crab apple varieties (Malus sp.), though non-native, are one alternative that appeal to both humans and insects.

Wild cherry trees have five petals per flower, but this “doubled” ornamental produces copious petals (possibly at the expense of quality nectar and pollen) that dissuade pollinators from visiting the flowers.
PC: Yoshikazu Takada, Flickr

One last note: to further help early-spring pollinators in a different way, try “leaving the leaves” until early-May. It is tempting to clean up your yard as early as possible, but many insects overwinter as various life stages in the messy leaf piles and ground cover, e.g. butterfly eggs, chrysalises, and adults of different species. Give them a chance to emerge by delaying your clean-up a few weeks. You’ll be rewarded when all these beautiful pollinators return to visit the flowers in your garden!