Sweet flag is a non-flowering, aquatic perennial, rush or sedge in the acorus family, native to Central Asia. Basal leaves emerge directly from a spreading rootstock, erect and sword-shaped, 3/4 of an inch wide and typically growing up to 30 inches tall. Leaves and rhizomes are sweetly scented when crushed, hence the common name. The genus name comes from the Greek for pupil, because the plant was used to treat inflammation of the eye. The species name refers to the plant's reed-like appearance. Easily grown in boggy, medium to wet soils in full sun or partial shade, Sweet flag appreciates afternoon shade, especially in hot southern summers. It will grow well in shallow standing water up to 9 inches deep as well as in consistently moist garden soil. It is grown primarily as an accent or specimen foliage plant in pond or water gardens, but it can be found in low spots, naturalized, or woodland areas as long as high soil moisture is maintained. To grow in a water gardens, plant rhizomes slightly below the soil surface in moist soils at the water’s edge or in containers set in shallow water. You can also plant rhizomes or existing clumps in containers sunk into wet boggy areas, which will prevent invasive spread. This plant does slowly naturalize by creeping rhizomes and can form large colonies in the wild. Insects, Diseases, and Other Plant Problems : No serious problems. Leaf scorch can occur if soils are not kept consistently moist.
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 sun (6 or more hours of direct sunlight a day) | Partial Shade (Direct sunlight only part of the day, 2-6 hours)
Soil texture
Clay; Loam (Silt)
Soil pH
Acid (<6.0); Alkaline (>8.0); Neutral (6.0-8.0)
Soil drainage
Frequent Standing Water | Occasionally Wet
Available space
Less than 12 inches
NC region
Mountains; Piedmont
Mature size
Height: 2 ft. 0 in. - 2 ft. 6 in. | Width: 1 ft. 6 in. - 2 ft. 0 in.
Growth rate
Medium
Maintenance
Low
Canopy layer
4 - Herbaceous (1-3 ft)
Form & Appearance
Habit / form
Clumping; Erect; Spreading
Foliage
Deciduous
Leaf color
Green
Leaf type
Simple
Leaf arrangement
Rosulate
Leaf shape
Lanceolate; Linear
Leaf value
Fragrant; Showy
Leaf size
> 6 inches long, < 1 inch wide
Hairs present
No
Leaf detail
Iris-like sword-shaped leaves 3/4 of an inch wide growing in basal clumps and reaching more than 30 inches tall. One margin of the leaf is wavy and it has a prominent mid-rib. Sweet fragrance when bruised. Sometimes the base of the leaves or their margins are slightly red.
Flower color
Green; Insignificant
Flower form
Insignificant; Spadix
Flower detail
Although it is non-flowering, greenish, 2 to 4 inch elongated spandixes, or spikes, appear in late spring.
Bloom time
Spring
Fruit type
Berry
Fruit detail
Sweet Flag is a sterile polyploid species and does not produce any fruit with fertile seeds.
Wildlife & Ecology
Native status
Non-native
Origin
Central Asia
Distribution
Europe, Canada and United States from Nova Scotia south to Georgia, west to the Mississippi, California and Washington state.
Wildlife value
Preferred host plant of a leaf beetle, Plateumaris shoemaker.
Food & Medicine
Fruit type
Berry
Uses (ethnobotany)
Rootstocks are used as a natural insecticide and an ingredient in perfumes.