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American Sweet Flag

Acorus americanus (AH-kor-us ah-mer-ih-KAY-nus)

Family: Acoraceae Native Herbaceous (3-15 ft)

American Sweet Flag is an evergreen, herbaceous perennial, aquatic rush or sedge, native to Siberia and the cold regions of northern North America and often found in wet open areas, such as marshes, or along the edges of quiet water. It is a member of the sweetflag family (Acoraceae) and, at maturity, can reach a height of 3 to 4 feet. The leaves have a citrus-like aroma, are white at the base, and usually green above, although there is sometimes a reddish or pink tinge at the base. Yellow inconspicuous flowers, 1 to 3 inches, bloom in spring and early summer. The genus name comes from the Greek for pupil, because the plant was used to treat inflammation of the eye. The species name indicates that this is an American species of the genus. In particular, it differentiates it from the similar, European species, A. calamus . The plants are so similar that A. americanus is sometimes considered a variety of A. calamus . American Sweet Flag is a freshwater aquatic plant that grows best in wet sites with full sun and does not tolerate shade. It does well in boggy conditions (shallow standing water up to 9 inches deep) and consistently moist garden soils. It will spread, at a moderate rate, by means of rhizomes. Kew Garden, which tracks the worldwide distribution of plants, notes that the plant has gone extinct in the southern part of its range (Virginia and states further south) and it is listed as a protected plant in Pennsylvania. To grow in a water garden, plant the rhizomes in moist soils at the water’s edge or in containers set in shallow water. Rhizomes or existing clumps can also be planted in containers sunk into wet boggy areas. Sweet Flag rhizomes and plants were valued by early Native American groups and were objects of trade and this probably led to the wide distribution of the plant across Canada and the United States. Plant populations often occur near old Native American village sites or camping areas. Diseases, Insect Pests, and Other Plant Problems: Susceptible to infection by Uromyces sparganii fungus. More information on Acorus calamus .

Source: NC State Extension Gardener Plant Toolbox ↗ NC State Extension Gardener Plant Toolbox, 44 attributes.

How it fits the guild

Guild layer 4 - Herbaceous (3-15 ft) Optimal soil pH Acid (<6.0); Neutral (6.0-8.0)
See companions & conflicts ↓

Companions & Conflicts

Curated pairwise relationships between this plant and others in the library — who feeds whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.

No curated interactions recorded for this species yet.

Also noted by NC State

Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.

Full plant profile

Growing Conditions
Plant type
Herbaceous Perennial; Ornamental Grasses and Sedges
Life cycle
Perennial
USDA zones
1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b
Light
Full sun (6 or more hours of direct sunlight a day)
Soil pH
Acid (<6.0); Neutral (6.0-8.0)
Mature size
Height: 2 ft. 0 in. - 3 ft. 9 in. | Width: 1 ft. 6 in. - 2 ft. 0 in.
Growth rate
Slow
Maintenance
Low
Canopy layer
4 - Herbaceous (3-15 ft)
Form & Appearance
Habit / form
Erect; Spreading
Texture
Medium
Foliage
Broadleaf Evergreen
Leaf color
Green; Pink; White
Leaf type
Sheath
Leaf margin
Entire
Leaf value
Fragrant
Leaf size
> 6 inches long, < 1 inch wide
Hairs present
No
Leaf detail
Iris-like, sword-shaped leaf blades (to 3/4 of an inch wide) in basal clumps are white at the base, sometimes with pink or red, but otherwise bright green above. Two to six major veins are raised above the leaf surface. The leaf is swollen in the center, tapering to the ends. Vegetative leaves are 3 to 4 feet, sheathing base is 6 to 18 inches.
Flower color
Gold/Yellow
Flower form
Spadix
Flower size
1-3 inches
Flower detail
Yellow flowers blossom from May to June. The plant's pollen grains are usually aniline blue.
Bloom time
Spring; Summer
Fruit color
Green
Fruit type
Berry
Fruit detail
Fertilized flowers produce berries with a jelly inside.
Wildlife & Ecology
Native status
Native
Origin
Siberia, Canada, south to Pennsylvania, west to Oregon
Wildlife value
Preferred host plant for the plateumaris shoemaker beetle
Food & Medicine
Fruit type
Berry

Uses (ethnobotany)

Leaves have been used to flavor beer.

Landscape Use
Landscape location
Naturalized Area; Pond
Landscape theme
Rain Garden; Water Garden
Design feature
Small groups
Garden tags
#water garden #rain garden #sedge #perennial sedge #rhizomatous #fragrant leaves #aquatic #drought intolerant #cold tolerant
Problems & Resistance
Resistant to
Deer; Erosion; Wet Soil
Propagation
Division

Planted at Hunnicutt

Nobody’s planted this one yet.