Answer: Assuming there are no changes and you do not live in an extreme climate, there are only a couple of reasons why they might not bloom.
They are too crowded or they have exhausted a poor soil. In either case here's what I suggest:
1. Immediately sprinkle a hand full of 12-12-12 around each plant, scratch it into the soil and water well. Then if you don't get around to the rest it should help next year. You should do this again in August.
2. In fall dig up the entire clump, divide it and replant. On an old plant you might get from 6 to 12 good divisions. Do not just replant it. Each division should have no more than 5 or 6 'eye' (pink buds) visible.
3. After it is dug and divided, fortify the old site- add a cup of bone meal and a good handful of 12-12-12. Mix in some compost, some manure, some sand etc depending on your soil condition. Mix well and replant at the proper depth.
4. Next year at least some of these divisions should bloom, but if not, it make take another year.
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