Never plant onions in the same area more often than once every four years. Plant in well-drained soil or raised beds. To avoid storage diseases, be sure onions are well-cured before storing. Avoid planting in soil known to be infested with nematodes. Onion maggots are attracted to decomposing organic matter.
Good sanitation is necessary to avoid maggots.
This results in small bulbs with large necks which are hard to cure and generally unusable. The larger the plants are at the time of exposure to the cold period the higher the incidence of bolting. Plant at the correct time for your area. Avoid high fertilizer rates applied in the fall. Heavy nitrogen application later in the season may result in large necks.