Acorus americana – American Sweetflag

General Information: Sweetflag is an herbaceous perennial commonly found in wetlands in Europe, Central Asia, and North America. Slender, grass-like, upright, lime green leaves arise from an underground spreading rhizome. The leaves sometimes develop a crinkled appearance as they grow, and give off a spicy, citrusy, somewhat sweet and musky smell when crushed. At maturity, the plant can reach heights of 5 feet. The inconspicuous finger-shaped flowers emerge in May and June. For most of the year, this plant’s reedy appearance makes for a lovely native addition to any moist or wet areas. Although naturally found in sunny waterways, swamps, and wet fields, we have found that this plant will tolerate drier areas in full sun once they have been given a year or two of extra watering to fully establish. They also do very well near downspouts and in areas where puddles form during rain storms. Sweetflag has a rich and deep history of medicinal use amongst the Indigenous Peoples of North America, Europe, and Central Asia. This plant is still widely used in folk medicine, modern herbalism, and Traditional Chinese Medicine.

Cultivation Details: If planted near Irises, care should be taken to differentiate the two, as Irises are toxic. There are two closely related species in the Acorus genus: A. calamus and A. americana. The Eurasian variety cannot propagate via seed and forms dense clonal colonies via rhizome, whereas the American variety can readily reproduce by reseeding. We are confident our plantings are A. americana, as they have been observed to develop mature fruits and reproduce via seed. An excellent choice in rain gardens, for rewilding, for medicinal herb gardens, or along wet borders.

Growing Requirements: Plant in full sun. Prefers wet soil. Will tolerate 1-3″ of standing water. Will tolerate well-drained soils if kept irrigated for 1-2 years. Propagate in late fall or early spring by rhizome division, or in early summer by seed.

Fun Facts: The name “Sweetflag” derives from the archaic name for Irises, “Flag,” to which the plant’s leaves and rhizomes bear a superficial similarity. Despite outward appearances, Sweetflag is only distantly related to Irises. High populations of this long-lived perennial are sometimes used as an indicator of pre-colonial villages in archaeological and anthropological studies. It is believed this plant was widely traded amongst Indigenous Peoples prior to the introduction of Eurasian Sweetflag in the 1600’s. Until just a few years ago, American Sweetflag was considered a subspecies of Eurasian Sweetflag (Acorus calamus). In the 1960’s, studies were conducted on the chemical constituents of the Japanese ‘Jammu’ strain of A. calamus which showed the Eurasian types produce a toxic compound known as β-asarone. This compound is absent from the American species, however A. americanus  is still banned as a food additive by the USDA as a result of these dated studies.