Division ÷ Dividing Perennials

Iris after dividing and cleaning.

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To dig up and split plants using varying degrees of physical force,

thereby increasing your plant stock and

improving the health, vitality, and blooming capacity of the plants.





  • You can tell plants need dividing if: the center crown dies; they raise up out of the ground as a result of crown density; plants stop or drastically slow down blooming.
  • Some plants MUST have regular dividing (e.g.: mums, German Iris)
  • Some plants don’t need dividing and stay put (e.g.: peonies, Dictamnus)
  • Get to know the individual requirements of your plants!



  • If plants bloom in the spring or summer, divide in the fall.
  • If plants bloom in the fall, divide in the spring (e.g.: divide mums and ornamental grasses in spring) Early fall bloomers can also be split in late fall after blooming.
  • Divide plants when weather is cool and damp: in southern CT, April to late May or mid September to late October.



  • Dig entire plant out of the ground, place on a tarp; never try to take a small piece of a plant out of the ground and leave the rest in—this is a great way to demolish a plant!
  • Once out of the ground, cut back bulk of foliage by at least 1/3, but no more than 2/3.
  • Look for natural separations in the crown—divide along these lines using various degrees of force (e.g.: trowel, sharp knife, spade, two pitchforks back-to-back, saw, ax, dynamite—just kidding!)
  • Prepare soil for replanting by digging deeply, then backfill, amending with rock phosphate, greensand, and compost to encourage strong root growth. Plant at same depth as before.



  • Mulch thickly around crowns to keep soil warm and encourage rooting. Water well and deeply for first two weeks.
  • Apply winter mulch of salt hay or evergreen boughs in late fall, after soil has frozen to keep it frozen and prevent heaving of crowns; apply Wiltpruf (an anti-dessicant) to the canes of roses.


In an effort to provide horticultural information, these educational documents are written by Nancy DuBrule-Clemente and are the property of Natureworks Horticultural Services, LLC. You are granted permission to print/photocopy this educational information free of charge as long as you clearly show that these are Natureworks documents.