Answer: Most perennials bloom for only a week or two once a year, so to have all season bloom you would need to plant a wide variety of plants. That space is quite narrow, but you might consider the following: creeping phlox (Phlox subulata), candytuft (Iberis), bearded iris, Siberian iris, perennial salvia, both lance leaf and thread leaf coreopsis, early and mid and late season daylilies, purple coneflower, black eyed Susan, perovskia, assorted sedum, boltonia, asters, mums.
If you truly prefer a full season of bloom you might look at annuals, the Wave series of petunias or a mass planting of marigolds for instance might do the job nicely.
Your local professionally trained nursery staff may have additional suggestions based on a more detailed understanding of the growing conditions (soil type, soil moisture, wind exposure, etc.) and your overall design goals. Enjoy your perennials!
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