Beans: Let them hang on the plants for a very, very long time, ideally until the pods are brown. You probably won’t want to do this during the middle of the growing season, as it will discourage further bean production. Unless, of course, you’re trying to discourage bean production.

Tomatoes: The jury’s out on whether or not your plants will cross-pollinate. The internets tell me that tomatoes planted close together mostly self-pollinate, but that you should expect a cross-pollination of 5 to 10%. Also, remember that seeds from hybrid plants will not breed true. It’s only worth saving the seeds from heirloom tomatoes. Tomato seeds are encased in a protective coating that needs to be removed before you save the seeds. To do this, squeeze the seeds and pulp into a jar with some water and let it sit a few days. When it’s foamy and smells nasty, you’re done. Pour off the tomato bits and any seeds that float, rinse the remaining seeds in a few washes of water, and transfer them to a plate to dry.

Peppers: Alas, peppers are promiscuous. If you’re growing a bunch of peppers together, or if you garden in a community garden, chances are that your plants have cross-pollinated and the seeds will not breed true. Of course, if you’re interested in hobby plant breeding, save away! Just cut out the seeds and let them dry.

Cukes, zukes, and melons: No idea if they cross-pollinate, since mine almost always die. I did, however, get one gorgeous melon. Melon seeds also benefit from fermentation. Just treat them like tomatoes. Who knows what will sprout from those seeds next year?

Lettuces, arugula, spinach, basil, etc.: Just let them go to seed and collect the dried flowers.

Potatoes and sweet potatoes: Set a few aside for next year.

Flowers: Cut off the heads of some you like and dry them.

These are the only things that I’ve tried, but I’m curious to hear your experiences. Any words or caution or wisdom?