Onions should be mature and dry when harvested. Unless crops are to be cured in the field, harvesting of dry onions usually starts when 60-80% of the tops have fallen over.
Formation of chlorophyll – green scales – in the outer skin can occur when crops are left to cure for too long or when bulb shoulders are exposed to sunlight in the field.
Bulbs need to be carefully handled to minimize bruising and cuts that can allow disease to enter.
Controlled atmosphere storage is increasingly practiced to maintain quality in store over longer periods and extend the marketing period. Also read: professional seedlings raisers
Maintaining CO2 levels at 5% inhibits fungal sporulation and O2 at 3% reduces sprouting.
Temperatures should be around 34°F to help reduce respiration and relative humidity kept at 65-70% in order to inhibit fungal spread.