I have May Night salvia which only blooms May and June. Which salvia for zone 5 would bloom all summer?
None of the Eurasian ones. These are all seasonal. Salvia pratensis hybrids like the nemerosas can rebloom (weakly) if dead-headed. The New World sages have some long-season forms such as those from farinacea and guaranitica, but none of these are hardy in USDA Zone 5.