Fava beans! Easy to grow, fun to watch, nice flowers, tasty, and big nitrogen nodules.
I planted $10 of Windsor beans 2 years ago and ended up drying about 300-400 seeds (far more than $10 worth) and still had too many to eat. Some of my new son's first solid food was a hummus made from those same dried beans (really delicious!).
Such a fun plant to grow. Processing the beans is a bit of work, but wow, it's worth it. Unparalleled flavour in the bean kingdom.
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