Certified GKH Gardening Expert
This should be done in early Autumn. The process will be easy, as long as you stay on top of keeping the seeds from getting infected.
Seeds must be soaked for about 5 days prior to prepping them for cold stratification. Change the water each day until the end of the 5 day period.
After, dry them off well and place into your seed starting soil. Place them outside out of direct sunlight for the duration of winter (since you are in a zone that is very close to the limit of the cold that they can stand, I would do this treatment and plant them about 2 months before Spring). They will need the cold to break dormancy. After about 2 months of keeping the soil moist, but not wet or dry, you will notice the first signs of life.
Here is an article to help you with their care after that: