PlantLife Online

Answer

Onions are ready for harvest anytime after the foliage is over 6 inches tall, they are fully mature when the above ground portion has fallen over. The key to preserving onions and to prevent bruising is to keep them cool, dry and separated. The best way to store onions is in a mesh bag kept in a cool dry place, onion do best when they are stored not touching one another. If it sounds like harvesting and storage are not the problem it is more than likely a soil-borne fungi or root maggots. Soil-borne problems can be managed but never completely eliminated, annual rotation of crops will help. To control root maggots the plating area should be tilled under at least two weeks before planting, planting starter plants rather than seeds will also help. There are also insecticides that can be used to control root maggots however they will kill beneficial insects as well. In a home garden situation I highly recommend adjusting cultural practices and exploring organic options before resorting to chemicals.