Symphyotrichum Here: Heart-leaved Aster, Blue Wood Aster
There are many native asters. Ask your nursery for the perfect (possibly native aster for your yard, example: New England Aster)
For the Blue Wood Aster
Height: 1 - 3 feet
Flowers: mostly blue, mauve, purple
Blooms: July - October.
Important source for bees and butterflies in fall.