Answer: Bush beans can be harvested as soon as they are large enough and firm enough to eat, and the harvesting encourages them to continue to produce more beans. Allowing beans to mature and harden on the plant will cause it to stop producing. Many people also prefer the younger beans because the inner seeds are still smalland the beans are more tender. Romana II for instance is described as having four and a half inch beans, so they are probably quite ready to pick -- generally you would not want to allow them to exceed the listed size so it is better to pick them on the small side.
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