I don't have an answer to your question, but I do have a question. How do you collect the seeds? I hope someone will answer your question, because I would like to know also.. Sorry to butt in..

Doesn't look like anyone got back to you. Collecting the seed from the little seed pods the imps form mid-late summer are fairly easy if you know what you're looking for - they look like buds but are green and resemble a football. Seeds should be brown (not white).

I would think you'd need to store them in a cool dry place until 8 weeks before your last frost date.