Illinois Native Plant Guide

Sweet Flag
Acorus calamus

Preferred Water Depth and Inundation Tolerance

Prefers 6-20 inches (Max: 24”/ Min: 0”). Species tolerates seasonal inundation, but may be killed by inundation of 1 foot or more of water for prolonged periods.

Wildlife Value

Provides waterfowl habitat. Muskrats will eat rhizomes. Wood ducks eat seeds. Medicinal plant with antibacterial compounds.

Application/Zone

Used in lower shoreline zones and vegetated swales. Rhizomes and roots form a mat in upper 4-8 inches of soil.

Availability, Establishment, and Maintenance

• Transplants, rhizomes and seeds are common and available from commercial vendors.
• Seeds may have dormancy requirement. About 90% germination is achieved by exposing freshly harvested seeds to cold, moist stratification for 60-90 days but seeds can be stored from 9 months to 2 years. Fall sowing provides better germination than spring by providing this cold treatment naturally.
• Rhizomes and transplants are generally more successful than seeds.
• Rhizomes are planted 2-5 inches deep. Root systems should be well-placed at a shoot base in the soil.
• Avoid flooding of newly established plants. Species requires drawdown until plants are established.
• For seed, some report 13 days are needed to germinate in a greenhouse without cold treatment. Survival rate in the field is 100%.
• Moderate rate of spread by rhizome, so use spacing of 1-3 foot centers.

Sweet Flag
Acorus calamus

Mature Height
2-6 feet

Plant Type
Perennial emergent herb

Indicator Status
Obligate

pH
5.9-8.8

Nutrient Load Tolerance
Low

Salt Tolerance
Low

Siltation Tolerance
Low

Flowering Color and Time
Green/brown
May 25 to June 30

Light Preference
Partial to full sun

Seeding Rate
.006 - .25 lbs/acre

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