A very light dose of fertilizer would be ok if you really want to fertilize, but I almost never fertilize beans. If they are growing well, are a good green color, they probably don't need it. Too much fertilizer will give you lush leaves, but very little in the way of beans.

Good luck!

when my of beans have their second set of leaves, I "hill them", that is I hoe between the rows and put more soil around the plants. At this point I usually mix a small amount, (maybe two small hands full per 12" row ) of 10-10-10 into the soil I put around them. That has always worked for me. As of today, my plants are full of blooms. Next week we are digging the potatoes and I'll plant more beans in that bed.