Acorus calamus
Common Name: sweet flag 
Type: Rush or Sedge
Family: Acoraceae
Native Range: North America, Asia
Zone: 4 to 10
Height: 2.00 to 2.50 feet
Spread: 1.50 to 2.00 feet
Bloom Time: Non-flowering
Bloom Description: Non-flowering (not showy)
Sun: Full sun to part shade
Water: Medium to wet
Maintenance: Low
Suggested Use: Water Plant, Naturalize, Rain Garden
Flower: Insignificant
Tolerate: Heavy Shade, Erosion, Wet Soil


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.

Noteworthy Characteristics

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. (particularly in the northeast and central portions) including a number of counties in the State of Missouri. 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 acorus 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.

Genus name is the Latin name from the Greek akoron used for Acorus calamus and Iris pseuodacorus.

Specific epithet is in reference to the plant's reed-like appearance.

Foliage and rhizomes are sweetly fragrant when bruised, hence the common name.


No serious insect or disease problems. Scorch will occur if soils are not kept consistently moist to wet.


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.