Amaranthus love lies bleeding
I live in western NY and I just bought a few 1' tall amaranthus plants. Could they still reach maturity planted this late in a pot? I do get about 4 hours of direct sun.
If you care for them consistently, they will definitely continue to grow but no guarantees on whether they'll be able to reach the full bushy look that they're known for.
Worst case scenario, they'll go dormant in the fall and you might try bringing the containers in for the winter (cut back on watering when you do).
This article has some tips on growing Love Lies Bleeding plants: