From the ArcaMax Publishing, Gardening Newsletter:
http://www.arcamax.com/news/gardening/s-156841-216302
Question: I have trouble starting wildflower seeds I have collected,
including milkweed and meadow rue. What do you suggest?
Answer: Many of the wildflowers (and perennials) seeds require a cold
period in order to germinate. If you try germinating them at room
temperature for several weeks with no results, try chilling them at
between 25 and 40 degrees for between several weeks and several
months. You can chill the seeds in packets or in pots of soil. Another
method some gardeners use with great success is to sow the seeds in
pots in late summer or fall and leave them outdoors in a sheltered
spot until they germinate in the spring. (If you do this be sure to
protect the pots from rodents and other animals.) Milkweeds generally
require 3 months of cold stratification; most rue (Thalictrum) need
about three weeks.