Acorus calamus commonly called sweet flag is a deciduous, spreading, marginal aquatic perennial that features iris-like, sword-shaped leaf blades (to 3/4” wide) typically growing in basal clumps to 30” tall. It is a sterile triploid. Although native to Europe, it was introduced into North America by settlers in the 1600s, and has naturalized over time throughout much of the U.S. Mature leaves have one slightly wavy edge and a prominent midrib. Plants thrive in wet, boggy soils and are commonly grown today as foliage accents in water gardens and pond margins. Although its foliage resembles that of a large iris, sweet flag is actually a member of the arum family. Insignificant tiny greenish flowers appear in elongated inflorescences (spadixes to 2-4" long without showy spathes), which appear in late spring. Flowers may give way to tiny fleshy berries. Foliage and rhizomes are sweetly fragrant when bruised, hence the common name.
Easily grown in average, medium to wet soils in full sun to part shade. Grows well in both boggy conditions (including shallow standing water to 9” deep) and consistently moist garden soils. In water gardens, plant rhizomes slightly below the soil surface in moist soils at the water’s edge or in containers set in shallow water. Rhizomes or existing clumps may also be planted in containers sunk into wet boggy areas to help prevent any possible invasive spread. Scorched leaf tips will occur if soils are allowed to dry out. Appreciates some relief from hot summer sun (e.g., afternoon shade or filtered sun) when grown in hot summer climates such as the St. Louis area. Slowly naturalizes by creeping rhizomes and can form large colonies in the wild. Mass or specimen for water gardens, stream or pond margins, bogs or in moist open woodland gardens. May also be used in other areas of the landscape, such as low spots, as long as its high soil moisture requirements can be met. Hardy in zones 4-10.
Growing Instructions for the Sweet Flag
The seeds have a period of dormancy. They can be planted outdoors in the fall or winter for spring germination or they can be cold stratified to simulate winter conditions and to break their dormancy at any time of the year. 1. Soak the seeds in water for 24 hours. 2. Put the seeds in a ziplock bag. 3. Put the bag in the refrigerator and leave it there for 2 months. 4. Put some potting soil in a container. 5. Sow the seeds on the surface of the soil. Press the seeds down slightly in the surface of the soil but do not bury them. Keep the soil very moist until germination. The seeds germinate in 14 days. 6. It is semi-aquatic and grows in shallow water or in wet soils. It can grow in normal soil but it prefers wet soil. When the seedlings are a few inches tall, they can be transplanted. Plant them in full or partial sun and in wet soil.