Broad beans

Hi all, i have started growing veg for the first time this year apart from tomatoes, anyway i planted some  broad bean plants in big tubs in the green house in May, they grew well and sprouted some pods about 5inches long, on opening the pods there were only one or two beans in each pod,what has gone wrong?some were even empty, any ideas? as i would like to try again next year.
thanks   

As said by MC - broad beans are hardy veg and need to be outside. If you just don't have the room, I'd suggest planting them a couple of months earlier, then when the flowers appear, tap the stalks so they get pollenated.