Bean seeds are really easy to collect and save for re-planting next year. The first step is make sure you are saving bean seeds from a well-established heirloom variety so you'll have the best chances at success. There are lots of heirloom bean varieties available to choose from. For pole beans, the Kentucky Wonder Pole is probably the most common. For bush beans, the Blue Lake 274 variety is one of the more commonly grown. Early Bush Italian is a common heirloom variety of flat bean, while Purple Queen is a common heirloom purple bean.
For best results, you want to leave the beans on the plant until they
dry out. The pods will turn brown and brittle and when you shake the
pod, you should be able to hear the hardened seeds rattling around
inside. At this stage, you can go ahead and pick the beans and bring
them inside to dry out a bit more. You can then remove the bean seeds
from the pods. Spread the seeds out on foil or a baking sheet and let
them air dry for another couple of days. You want the seeds to be hard
and shriveled up a bit. Then you can then put the seeds inside an
envelope and store them in a jar in your refrigerator. Make sure you
label the envelope so you know what seeds it contains. If you are
saving lots of different seeds, several envelopes can fit inside one,
quart-sized jar. It's also a good idea to put a tablespoon of dry rice
at the bottom of the jar just to absorb any moisture.
Click on the following links to learn more about growing green beans.