So many factors go into why a plant fails to recover after division.....i.e., what kind of soil you have, what you added to the planting hole, what your weather conditions were like, what time of year you did the division, what sort of injuries the plant sustained when you divided it, pests that are present like voles and shrews who love the easy digging around new divisions, how often you watered the plant, etc. If the plant was healthy and growing well before it was divided, I would look at other factors. I find the best time to divide is 2 weeks after blooming when plants (after resting for those two weeks) go into a period of rapid growth and increase. But you can't do that in every climate. Some plants do hit the ground running faster than others....and that goes to plant vigor. After division, the plant has to establish again for the flower and scape height to look as registered again.
