Some plants are stimulated to bloom by day length, David. So they are small and just starting up in May when the day length would be right for bloom to start, but then must wait until the days get shorter in August or September for their next round of bloom. I believe chrysanthemums are this way. If you have the plants up to blooming size in the spring they might bloom, then stop during the long days in June/July.
Others are stimulated by temperature change, and some just take longer to mature to blooming size.
Btw, you don't need to "quote" each of our posts to answer.
