While the Cyms do need light and feeding, I'm not convinced that the light is that important. I have mine scattered from full sun to almost full shade, and everything in between, and all are full of spikes, with the exception of the one that had it's spike broken off. I really think the temps are the key to blooms. We had a cooler summer than normal this year, and lots of up and down temps in the fall, and mine are doing much better than last year. It does depend on the cultivar though...some will take more heat than others.
