Perennials for Summer and Fall
Q.Which perennial will flower throughout the summer and into fall?
A. Remember that perennials don't look their best the first season, plus you'll need to plant a variety, not just one. Having said that, planting several of these will bridge the gaps:
Start with one-gallon plants, choosing plants with plenty of healthy, lush foliage and avoiding those that have already started blooming. Give them the conditions they need (shade or sun, moist or dry), then be patient. The first year you'll probably get only a few flowers, the next year many more, and the third year, you'll be astounded at the color you've created.