Expert: Long Island Gardener - 9/8/2006

Question

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Followup To

Question -
My zip code is 52807,

Is Spring or Fall the best time to separate iris?

Answer -
No doubt about it - do this ASAP.

If you wait until spring, when growth has resumed, you interfere with the normal growth cycle - enough to disrupt flower production.  All efforts from broken dormancy until the last spent bloom are spent on flower production.

You may know that dividing Irises is an exercise that should be done every 4 or 5 years to maintain vigor.  Some Iris collectors schedule this work 6 to 8 weeks after bloom has finished, provided the weather is not too hot.  

But general wisdom says optimal timing is reached as the summer wanes -- this allows for strong root development before a deep solid freeze sets in.  

Don't be surprised if the new divisions take a year or longer to bloom.

North Dakota State University devotes a full webpage to the subject of Irises (www.ext.nodak.edu/extpubs/plantsci/landscap/h113w.htm).

Have you done this before?  Any questions?

Answer
Fall is much better than spring.  As noted earlier, you don't want to interfere with the natural flowering cycle.  If you divide in spring, there is a chance you will interrupt flower production.  Do this asap.  Before it's too late! You want to get those roots started.