Preventing Seed Production

• The iris reproduces both from seed and via underground rhizome. However, allowing your iris plant to make seeds can drain its energy and prevent it from successfully storing up food for the cold season. Cutting back irises to prevent seed production can also increase the chance of a second bloom in the fall. The University of Minnesota recommends removing the flower stems as soon as blooming is done, leaving only about an inch of stem above the rhizome. This prevents seed formation and encourages the iris to flower again.
  
  

Division

• Older iris plants can become crowded. Over time, these flowers produce more and more rhizomes, resulting in a densely packed bed of flowers that may decline in health. Once irises go into summer dormancy, dig up the whole clump, wash off the soil and separate the rhizomes into separate fans. Replant healthy fans from the outside of the clump, trimming off broken roots and cutting back all leaves to around 6 inches in height. If immediate planting isn't possible or desirable, you can store divided iris rhizomes in a cool, well-ventilated area for several weeks.
  
  

Fall Cleanup

• Removing iris leaves and other debris in the fall can help keep them in good condition over the winter. After the first hard frost, or when iris leaves yellow, cut back the tops to around 6 inches high. Remove any dead stems or other debris. After the ground freezes, mulch the tops with 4 to 6 inches of compost, leaves or straw to protect the irises from severe cold. Remove the mulch in spring to encourage fresh growth.
  
  

Warning

• When cutting back or dividing irises, take care not to damage the rhizome. Rhizome injuries can lead to soft rot, a bacterial condition that causes rhizomes to become mushy and smell bad. Bad drainage or use of fresh manure as a mulch can exacerbate this condition. If an injured plant develops soft rot, dig up the rhizome and destroy all diseased parts. Inspect rhizomes for soft rot when dividing older irises.