Difficulty rating: easy
Suitable growing site: open ground or large pot - balcony, garden or allotment
Days from sowing to harvesting: 50-90 days 
Risk of cross-pollination: low
When to sow: sow bean seeds in april in pots seedling compost or multi-purpose compost. for later crops, sow seeds directly outside in late spring. Plant out after last risk of frost. 
Requirements: good quality soil, and regular watering. 
Harvesting for eating: varies by variety.
Harvesting for seed collection: towards the end of summer, when the beans become full and pod skins become thin and dry.
In this video Vicky explains how to save seed from onions: