Oriental poppies (papavar orientale) resent being transplanted due to the fact that they have a very deep tap root.   Shallow planting is often the cause of failure, as is soil that is too wet. Division is needed only every 5 years or so and the best time to divide or transplant is in August when plants are dormant.

Transplanting an entire clump is much easier than trying to divide the clump.  They are best divided by large root cuttings.  However, if your clump is large, you can perhaps slice off a DEEP section at the edge of the clump and successfully transplant it to a properly prepared site. Information re. how to best grow poppies can be found on this site:

http://www.whiteflowerfarm.com/how-to-grow-oriental-poppies

If you have additional questions, please let us know.