I tried with sweet peas one year here in FL. I'm zone 9a. They sure do have the most heavenly scent, don't they?
Started the seeds in December, so that they were getting to blooming size just when the weather started warming up in February. They bloomed nicely for about a month, then something developed a taste for them, and they gave up.
I think the 'secret' is starting the seeds when the weather's still cold, and don't water too heavily before they are up or the seed rots. Protect the little plants on cold nights so they don't freeze and don't expect them to keep blooming very long once it really gets warm. The Pacific Northwest is The Place for growing sweet peas. They just love the long spring and cool, moist weather up there. I'd go for a spot with afternoon shade to try to keep them going a bit longer.
I gave up after that one effort, as it seemed like too much trouble for too little reward. Yours may bloom longer than mine did, though as you are further north.
