Acorus calamus aka Sweet Flag

Acorus calamus, or sweet flag, belongs to the Acoraceae family. Kew places its native range in Central Asia’s Irtysh valley. It now grows across Europe and parts of North America. This deciduous perennial grows along wet banks and pond edges. It forms upright clumps that spread through creeping rhizomes. Garden plants reach about 2–3 feet [0.6–0.9 metres] tall. RHS gives an upper height of 3.3 feet [1 metre]. Clumps spread 1.5–2 feet [0.46–0.61 metres], or 3.3 feet [1 metre] in RHS records.

The green leaves rise straight from the spreading rootstock. Their long, narrow shape looks much like an iris leaf. Each blade has a clear midrib and one wavy edge. Some leaves show red at their base or margins. Crushed leaves and rhizomes give off a sweet scent. The leaves die back rather than staying green all year. Small flowers sit on a spadix beside a leaf-like stem. Sources place these spikes from late spring through midsummer. They range from greenish to brown and draw little notice. The sterile plants described by NC State lack fruit with fertile seeds.

Sweet flag grows in full sun or part shade. Afternoon shade helps where summers bring strong heat. It needs soil that stays moist or wet throughout growth. It also grows in shallow water around pond margins. Sources give a water depth limit near 0.75 feet [0.23 metres]. Clay and loam suit it, across acid, neutral, and alkaline soils. Its listed hardiness covers USDA zones 4–10 and RHS H7. Dry soil can scorch the leaves and their tips.

Gardeners use it for foliage rather than a flower display. It suits water gardens, rain gardens, and wet woodland edges. Groups can fill damp low spots or line a stream. Creeping rhizomes can spread into broad colonies over time. Sunk containers help keep that spread within bounds. Divide clumps every few years to ease crowding. Sources report few major pest or disease troubles. NC State names it as a host for a leaf beetle.

People have used its leaves for mats, baskets, and thatch. The rhizomes supply scent for perfumes and insect-control products. Recorded food uses include leaves, stems, and rhizomes. These uses do not establish that eating it is safe. Fresh roots can be poisonous, and isolated oil poses risks. Some plants contain asarone compounds linked to possible cancer risk. Traditional medicine also uses the rhizome, with the same safety concerns.