Dividing Bearded Iris

  • Bearded iris can be divided any time after the last spring frost. However, many iris growers believe the optimal time is 6-8 weeks after blooming. August is a good time to begin. This gives plants time to root well before winter. Extremely hot days (90 +) should be avoided when transplanting.
  • Plant division every 3 to 4 years is beneficial for maximum bloom. With a garden fork lift the entire plant clump and shake or rinse excess soil from roots. As you divide the clump break or cut off old stems and/or any diseased plant material. Keep only vigorous portions with healthy thick roots. Trim leaves of each division to a fan shape 6 to 8 inches. Remove any iris borer in the leaves or rhizomes. Burn or discard diseased plant material. Do not add to a compost pile. Lay rhizomes in the sun to dry for a couple days before replanting.
  • Re-work the soil in the existing bed or prepare a new bed. Be sure soil is well-drained and receives at least 6 hours of sunlight each day. Plant newly divided fans making sure the top surface of the rhizome is level with or just slightly below the soil surface.  If you bury the rhizome too deeply, the plant may not flower. Do not mulch directly over iris rhizomes. Mulch tends to retain too much moisture and may promote bacterial soft rot. Iris should be planted about 2’ apart with no other plants nearby to overgrow them and compete for soil nutrients. Or you can plant rhizomes in a triangle 1’ apart with the leaf fans facing outwards to produce a clump effect.
  • Water newly planted iris deeply once a week for the first month if there is not adequate rainfall. Avoid frequent shallow watering. Over-watering is another common cause of soft rot problems.
  • Each fall and spring remove dead leaves and diseased parts and burn or discard material. Keep the soil surface cultivated lightly but try not to disturb the roots.
  • Instead of digging entire clumps, plants can be rejuvenated for a year or two by removing the old rhizomes at the center and leaving new growth in the ground.
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