I found this interesting and plan to try it on some of the hard/woody type seeds.
Speed germination of flower seed:
You can get woody seeds, such as moonflower, passionflower, morning glory, and gourds, off to a healthier start by lightly rubbing them between a couple of sheets of fine sandpaper-and soaking them overnight in a solution of 1/2 cup apple cider vinegar and 1 pint warm water. Next morning, remove the seeds from the solution, rinse them off, and plant them.
