Milkweed is known to be slow to germinate. Stratifying the seeds helps. Sprinkle seeds onto a moist paper towel, fold the towel, and insert it into a plastic bag. Place the bag in a refrigerator for 2-4 weeks. After that, sow seeds indoors in a warm and bright location. Plant seeds no more than 1/4" deep; they need light to germinate. Keep moist but do not over water. Transplant outdoors when danger of frost is past.