Planted in 2009 to test hardiness of a sheltered spot in the garden. For added protection, a large flowerpot covered the shrub during the winter months, and the shrub bloomed profusely in those years.
When the shrub grew larger, a garden blanket replaced the flowerpot. At that point, the flowering decreased and eventually stopped, and so did the pruning.
Last fall, I gave it the same treatment I give my roses. Cut down to a third and cover with shredded leaves just before the soil freezes. Then during the winter months, pile on snow. In the spring, cut stems by a third and leave the shorter as is. It finally bloomed again.
After reading instruction on the White Flower Farm, I realize the lack of pruning may have contributed to the blooming problem.