Onion bulbs are stored well at

Onion bulbs are stored well at 0° to 1°C.
In cold storage onions are stored in the temperature range between 0° to 1°C. under this low-temperature condition onions will not respire, thus there will be the least loss of water, keeping them fresh for a long period.
On top of this, between 0° and 4° Celsius, onions can be kept healthy and suitable for storage for up to 12 months.