Lobelia siphilitica – Great Blue Lobelia; Blue Cardinal Flower

General Information: Great Blue Lobelia is a unique perennial wildflower that enjoys slightly shaded, moist areas. Spikes of bluish-purple Iris-shaped flowers emerge from late July to September and attract many pollinator species. The plant is also a host to several Butterfly and Moth species and is otherwise unbothered by pests and disease. The flowers range in color from pale purple to vibrant blue depending on growing conditions and genetics. These plants are widely regarded as persistent perennials, however they are quite unlike many others. Instead of regenerating each year from the root, Great Blue Lobelia dies back at the root after flowering. The areas where the stems and leaves meet (axils) sprout new roots during this time, and the plant’s lifecycle continues for another year. A showy and useful medicinal plant that is just as at home in an apothecary garden as in a wildflower sanctuary! Although this plant contains some toxic compounds, knowledge of the medicinal qualities of this plant have been utilized by Indigenous Peoples for millennia. Today they are chiefly enjoyed by native plant enthusiasts. In the Northeastern US these plants are becoming scarce in their natural habitats, making this species an excellent selection for rewilding.

Cultivation Details: These plants thrive in areas with indirect, dappled, or periodic sunlight. Consider Great Blue Lobelia in moist areas along the north-facing wall of structures, along forest and field margins, in glades, woodland gardens near bodies of water, or along the edges of paths. These plants spread prolifically by seed wherever the soil is bare. Their spread can easily be controlled by weeding or regular mowing, however periodic mowing (once every month) reduces the plants to the basal leaves and allows them to regenerate if they are desired as a feature along paths or walkways.

Growing Requirements: Plant in full sun to nearly full shade. Plants in full sun may mature quicker and have a lighter color than those in some shade. Additionally, plants receiving a lot of shade tend to grow leggy, fall over, and may require staking. Tolerant of most soil types. Uniquely tolerant of wet clay soils. Prefers a rich layer of organic matter. Prefers moist to wet soil. Does not tolerate dry soils. Suitable for mildly acidic, neutral, and mildly alkaline soils.

Fun Facts: Although the species name siphilitica implies that this plant is useful as a cure for the disease, this is likely due to a misunderstanding. Indigenous Peoples used the fresh plant, in combination with several other herbs, on those afflicted with syphilis. When settlers learned that this herb was a chief ingredient in the treatment, they sent great quantities of the dried herb to Europe in hopes of providing a cure. The dried plant alone is an ineffective treatment, however. Recent analysis has shown that the fresh root contains volatile oils that evaporate upon drying, which likely contributed to the success Indigenous Peoples had over European settlers in treating the disease.