Q.What Kind of Beans Are Growing in My Garden?
Hi. I have a daycare at my home and early this spring, as a sensory activity, we had the kids play with an assortment of dried beans outside. The beans were several years old, so I didn’t think much of them growing later! When we finished playing, we cleaned them up and put them in the compost. Now, I have several bean plants growing in strange places–including my garden where I thought I had planted green beans, and I have no idea what kind they are or how to harvest them. I picked a few pods today, assuming they were green bean volunteers from last year. . . .they are definitely not green beans! Some of the plants are viney; some are not. One has purple flowers–black beans?, but most have white. One plant has thin pods that are green with purpley-brown spots. Most have large pods with large whitish beans inside, and the pods feel thick and a little bit furry. Also, can we do anything with the pods I’ve already picked, or do we have to throw them away?

Certified GKH Gardening Expert
Seeds can save for years (the oldest recorded germinated seed was 2,000 years old!) so it is not surprising that they germinated.
What they are is hard to say, but it is safe to say that they were all dry bean varieties. The large whitish beans are likely a lima or fava bean. The spotted could be a pinto or cranberry beans.
Regardless, they are harvested the same way. This article will help with that:
https://www.gardeningknowhow.com/edible/vegetables/beans/harvesting-beans-when-do-you-pick-beans.htm
You can eat "shelling" or dry beans like green beans if you pick them while they are green. The pods do tend to be more fibrous, but they are certainly edible and worth trying.