well, that's the easiest question i'm likely to have this year.
Rozanne. blooms may through october.do a search and you'll find lots of threads on it. the only plant that competes with it for length of bloom in our gardens- is corydalis lutea.
best,
mindy

Pink Penny and sweet heidy are two others that are reputed to bloom very long as well. Johnson's blue isn't very good, IMO, it tends to get leggy.