Illinois Native Plant Guide - Sweet Flag - Pages 30-31
Illinois Native Plant Guide
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
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
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.
Perennial emergent herb
Nutrient Load Tolerance
Flowering Color and Time
May 25 to June 30