"David E. Ross" advised:

Try impatiens.

What about petunias? They'll bloom as long as you keep feeding, watering,
and pinching off the spent blooms. There are many varieties made for
hanging baskets, and if you bring them indoors in the fall, they'll continue
to bloom. I've done it, but have to admit, that after a while they get to
be too leggy and not nearly so nice, so then I throw them out to freeze and
die.

~~ Shelly ~~