Whoa, you're in a much colder zone than I am! Would coreopsis work for you? If so, how coreopsis 'Moonbeam'?
Do lupins grow as far north as you are? My son and his brood live in downeast Maine, zone 5, and lupins grow wild around there. Talk about low maintenance!
Good luck with whatever you plant--I know, you just want ot arrive on the weekend and something in in bloom. Wish I could help more...........

How about purple coneflower or black eyed susans. I would suggest ordering a catalog and looking through it for plants in your zone. They usually give descriptions on growing conditions too. You could also find what you like and then post a question about those particular plants.I think you probably have many choices!!! Happy gardening!!!

Are there any deer there?

Yes, I do have deer, but they don't pose a problem. They pass through the property to get to the lake, I have seen them munching on white spruce saplings but that's about it. Our local village feeds them all winter and spring long, so they are well taken care of. I should have been more specific I think. I do have native flowers: daisies, hawkweed, violets, black eyed susies, foam flower, trout lily, etc. I have planted from seed most other perennials: coneflower, monarda, lupin, liatris, geranium, dianthus, hollyhock, primrose, sedums, and thymus even the delphiniums. As beautiful as the delphs are they are rather fussy, that's exactly what I am trying to avoid. I'm extending the garden once again and looking for other ideas. (I am slowly getting rid of most of my lawn!)

Linda

What about yarrow/achillea? It's actually kind of invasive here in GA.....all I do is cut off the dead flower stalks, but you could leave them on for "winter interest" if you wanted, maybe they would look nice in the snow (which we do not really get).

Thanks for all your input.
I have wild yarrow, grows everywhere. Winter interest plants are limited, we get at least 3ft of snow in winter,
matter of fact there is still close to a foot on the ground, ugh it's april 9th for cryin out loud!!!

Centranthus ruber .. deer resistant, blooms a long time, reseeds, hardy to zone 4

Zebrinas they grow and bloom all season long right up to a hard frost. Also veronica has a long blooming period shasta daisy are good for your zone

Dragon's blood sedum. It doesn't die away completely, but the leaves turn a cool dark red in the fall, at least mine does. It doesn't spread aggressively, but if you pull off a stem and drop it, it will probably root. It's nice to edge beds too.

Doronicum
Omphalodes
Campanula Kent Belle
Camellias
Brunnera

Anything that lives in my garden has to be low maintenance :). What works for me in zone 4: purple coneflower, black-eyed susan, phlox, peonies, and daylilies, daylilies, daylilies!

Any kind of sedum would be nice. Drought resistant too.

I'll echo folks recommending Sedum. I have August Joy and found that it's happiest when I just leave it alone! Just picked up some Ruby Glow Sedum for their pretty purple foliage.

Columbine, Hosta and ferns for any shady spots. I didn't do a thing to my New England Asters this year and they made themselves bushy. Each plant has gone crazy into hundreds of branches. (Not sure if all of these are hardy up there.) Larkspur aren't technically perennials, but they're pretty reliable re-seeders!