What are the differences between the native wild lupine and bigleaf lupine commonly seen in New Hampshire landscapes?

During the month of June, lupines are in their prime blooming period throughout New Hampshire and New England and can be a stunning sight to see in gardens, meadows and roadsides alike. However, the lupine species we most commonly see today is a naturalized, nonnative species from the Western U.S.

Bigleaf lupine (lupinus polyphyllus) and the related ornamental Russell hybrid (Lupinus x regalis) were introduced to the northeast for both gardens and roadside stabilization in the early to mid-1900s. Through its intentional planting and as a garden escape, the bigleaf lupine rapidly spread throughout the landscape. It's been admired by many, but closely monitored by others as a potentially invasive species.

Adaptable to a range of habitats, bigleaf lupines spread easily through prolific seed production and have been known to displace native plant populations as their dense stands grow. Although providing pollen to local pollinators, it does not serve as a suitable larval host plant for any butterfly or moth species, despite its similarities to the native sundial lupine (L. perennis). 

In contrast, the sundial lupine is the sole host plant to New Hampshire’s state butterfly, the endangered Karner blue. Unfortunately, the tendency for bigleaf lupines to hybridize with sundial lupines from cross-pollination is common, which leads to hybrid plants that are also not suitable food sources for Karner blue caterpillars. Although true sundial lupines have become rarer, recent conservation efforts have been made to restore wild populations in their natural habitat around the pine barrens of Concord. 

So, how can you tell the difference between sundial and bigleaf lupines? Bigleaf lupines are primarily taller and have larger leaves than the sundial lupine and grow up to five feet tall, whereas the sundial lupine typically only grows to around two feet. Sundial lupines have 7-11 leaflets per leaf, while the bigleaf lupines have 11-17 leaflets. Additionally, the raceme (the flower stalk) of the bigleaf lupine grows 8-16 inches long, while the raceme of the sundial lupine grows to a length of 4-8 inches. Additionally, the flower color of sundial lupines is traditionally lavender-blue whereas the bigleaf and Russell hybrid flowers can either be a deeper shade of purple-blue or come in a variety of other colors (shades of purple, pink, yellow and white.) 

When considering to plant sundial lupine in your garden, be sure to purchase sustainably-sourced seed and plants that come from non-hybridized plants. 

Cultivation specs: sundial lupine prefers dry, sandy and infertile soils (does not tolerate poor drainage conditions) and full sun to partial shade. Unlike the bigleaf lupine, sundial lupine can spread both by rhizomes and seed. As legumes, all lupine species contain nitrogen-fixing bacteria in their roots, which improves soil fertility.