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Illinois Native Plant Guide - Sweet Flag - Pages 30-31

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.


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 Sweet Flag
Acorus calamus

Mature Height
2-6 feet

Plant Type
Perennial emergent herb

Indicator Status


Nutrient Load Tolerance

Salt Tolerance

Siltation Tolerance

Flowering Color and Time
May 25 to June 30

Light Preference
Partial to full sun

Seeding Rate
.006 - .25 lbs/acre

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