Experts and BHG readers answer.
Longest blooming plants
You are right to want to get the most out of the growing season. Perennials that bloom for more than two weeks in your area include:
Achillea spp. (Yarrow)
Agastache spp. (Hummingbird Mint)
Antirrhinum x ""Dulcinea's Heart' (Perennial snapdragon)
Artemisia 'Powis Castle' (doesn't bloom, but gray-green foliage is long-lasting)
Asclepias tuberosa (Butterfly weed)
Aster novi-angliae 'Purple Dome' (Blooms in fall, lasts all season)
Ceratostigma plumbaginoides (Dwarf plumbago--true blue flowers in late summer, foliage turns red and bronze, lasts until frost)
Coreopsis spp. (deadhead for continuous bloom)
Delosperma cooperi (Ice plant)
Dianthus gratianopolitanus 'Fire Witch'
Gaillardia 'Arizona Sun'
Salvia 'May Night' and many other salvias (Sages)
Santolina chamaecyparissus (deadhead for long blooming performance)
Sphaeralcea munroana (Orange globe mallow)