When is the best time to dig up, separate and replant Siberian irises?

They can be separate in early spring before growth and blooming or late summer after blooms.

Recommended transplanting is mid September

I agree with both ladies about timing of transplanting. Be sure not to bury the rizomes too deep and the soil should be well draining. I have beauties that are decades old. They are low maintance and only need seperated when crowded and a yearly dose of organic fertilizer. I use wood ash every fall. Good luck and enjoy! I have even potted some in large tubs and they do fine here in Pennslyvania!

Fall is the best time, but just make sure they are done flowering whenever you do it. The rhizomes want to be 1/2 open to the sun and air. Iris rhizomes will rot if they are put underground like other bulbs. Easy to transplant!