Hi Gmom,
I think you might be misunderstanding about drying seeds. You do not have to let seeds dry on the plant or cut stems to hang and dry.
First you need seeds to become completely ripe on the plant before collecting. At this point the seeds and/or seedpod may seem very dry, but that isn't true. When seeds are ripe, they are pretty dry and hard, but there is still residual moisture that can not easily be detected. Beans are a good example of this. When the seed is ripe, the bean pods are dry and leathery and the beans are shiny and hard. The beans are not completely dry though. If you took a hammer to them, they would smush, because there is still moisture within. So seed should not be left in plastic or packed up into little plastic baggies immediately after collection. Doing that will lower viability and possibly kill all the seed.
They need to be left in paper bags or on paper plates(any way that promotes a dry environment) for a week or more if you plan on putting in plastic. I prefer longer to be safe. Tiny seeds of course dry quickly. Large seeds like beans take longer, and bean seed once dry will shatter.
Storing your seeds in paper envelopes solves a lot of problems. Then if you like, you can put the seed into the small plastic baggies when shipping them out for trade.
Hope that all made sense,
Remy

This is my first attempt at gathering seeds from my flowers. Do I keep the seeds in/on the head? or removed them and set them on the paper plate to dry. I'm gathering marigolds and bachelorbuttons. All my other flowers are perennials, so they should come back next year on their own.

Hi Lindacatherine,
You can do either. My mother-in-law would cut the heads off into a paper bag with excess room(not packed tight into the bag) and keep them like that over the winter. She like you only saved a few types of seeds each year. I save lots of seeds and keeping seeds like that takes room that I don't have so I remove the seeds let dry and then pack into smaller packets.
Remy