Common Name: grassy-leaved sweet flag
Type: Herbaceous perennial
Family: Acoraceae
Native Range: Eastern Asia
Zone: 6 to 9
Height: 0.50 to 1.00 feet
Spread: 0.50 to 1.00 feet
Bloom Time: May to June
Bloom Description: Yellow-green
Sun: Full sun to part shade
Water: Medium to wet
Maintenance: Low
Suggested Use: Ground Cover, Naturalize, Rain Garden
Flower: Insignificant
Leaf: Fragrant
Tolerate: Heavy Shade, Erosion, Wet Soil
Culture
Easily grown in average, medium to wet soils in full sun to part shade. Plants perform well in both boggy conditions (including shallow standing water to 3-4” deep) and consistently moist garden soils. Never allow soils to dry out. Scorched leaf tips and withering leaves are often the first signs of drying soils. In water gardens, plants are typically planted in containers with water covering the crowns or in wet soils at the water’s edge. Plants appreciate 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. Plants will slowly naturalize by spreading rhizomes, but are not considered to be invasive. If grown in containers sunk below the water surface, plants will not spread. Plants are not considered to be reliably winter hardy in the northern parts of USDA Zone 5.
Noteworthy Characteristics
Acorus gramineus is commonly called grassy-leaved sweet flag. It is native to wetland areas of China, Japan, Korea, India, Thailand, Myanmar and the Philippines. It is a semi-evergreen, marginal aquatic perennial that features a grass-like tuft of narrow, linear leaf blades (1/4“ wide) that fan outward to 6-12” tall. Tiny, insignificant, yellow-green flowers bloom from spring to early summer on lateral, sedge-like flower spikes (spadixes to 2-4" long). Flowers give way to very tiny, reddish, fleshy berries. Tufts will slowly spread over time by rhizomes to form a dense ground cover. Plants thrive in wet soils and are commonly grown in water gardens and boggy areas for foliage accent or ground cover purposes. Although it looks like a grass and its common name suggests a grassy appearance, grassy-leaved sweet flag is not a member of the grass family. Originally it was assigned to the arum family (which includes calla lily and jack-in-the-pulpit), but recently it has been transferred from arum to its own family called Acoraceae. Transfer from the arum family was in part done because plants in the genus Acorus do not have true spathes as are typically found in arum family members. Foliage is sweetly fragrant when bruised (hence the common name of sweet flag).
Genus name is the Latin name from the Greek akoron used for Acorus calamus and Iris pseuodacorus.
Specific epithet comes from the Latin word meaning grass.
Foliage is sweetly fragrant when bruised (hence the common name of sweet flag).
Problems
No serious insect or disease problems. Scorch will occur if soils are not kept consistently moist to wet.
Uses
Mass as a ground cover in small areas of water gardens, along streams or ponds, bogs or in moist open woodland gardens. Helps control erosion on water banks. Also effective in rock gardens, border fronts, foundations or as small landscape accents as long as the soil moisture requirements can be met. This plant may be used in the landscape in somewhat the same situations as one might use those species of Carex that prefer sun/part shade.