Q. How do I plant Jack-in-the-Pulpit (Arisaema triphyllum) seeds?
Growing Jack-in-the-Pulpit from seed is fairly easy and can really be done with no special treatment. Simply plant the seeds now outside in a container. They should be planted about 1/2" deep and separated by 1" or so. They will germinate the next spring. The little plants can then be separated and planted in full to part shade where you want them to live. Be sure the container is where it will get the winter rain and snow. Watch for critters digging in the container!! Since you probably have more seeds than you want to put in containers, also simply plant some of the seeds 1/2' deep in a shady spot directly in your garden. Some of these will probably germinate also.
If you want to maximize the germination rate, leave the berries outside, unplanted in the cold until January or February. Then bring them inside and remove the pulp from around the seed. Since the pulp irritates some peoples skin, use rubber gloves when removing the pulp. It may not bother your skin, particularly if you rinse your hands well under water. To further maximize germination, put the cleaned seeds in a tea sieve and place in the tank (not the bowl!!)of the most frequently used toilet for a month or so. This will give the seeds a frequent washing with cold water. The seeds can then be planted outside in a shady spot in your garden where you want a plant.