What temperature is best for storing onions?
Written by
Liu Xiaohui
Reviewed by
Prof. Charles Hartman, Ph.D.Temperature for storing onions significantly impacts their shelf life. I learned this the hard way as I lost bulbs to sprout and freeze. Keep it at 32 to 36°F all the time! Note that once the temperature reaches 40°F, the sprouting process accelerates. Below 32°F, your onion commits cellular suicide by freezing in storage.
Danger Zone (40°F+)
- Triggers sprouting within weeks as bulbs break dormancy. Sprouts draw moisture from bulbs causing shriveling. I lost a whole harvest before installing temperature alarms.
Ideal Range (32-36°F)
- Maintains dormancy preserving firmness for 6-12 months. Enzymatic activity slows without stopping completely. This sweet spot prevents both sprouting and freezing damage.
Freezing Risk (<32°F)
- Ice crystals rupture cell walls causing mushiness. Damaged bulbs leak fluids promoting mold. Once thawed they spoil within days. I measure temperatures twice daily in winter.
The placement of the thermostat is important. Locate sensors amidst the onions, rather than adjacent to any walls. I now use wireless units that send alerts to my phone, since temperature spikes ruined previous crops. Keeping a close eye on my crop at all times helps avoid minor issues from becoming major disasters.
Humidity control works with temperature. Maintain a humidity level of 60-70% at storage temperatures. Higher levels cause mold, while lower levels dry bulbs out. I use hygrometers in conjunction with thermometers for comprehensive climate control.
Insulation Methods
- Use foam panels or straw bales around storage containers. Prevents outside temperature fluctuations affecting bulbs. I maintain steady conditions even during heat waves.
Air Circulation
- Install computer fans in enclosed spaces. Prevents cold spots where freezing occurs. I run mine 10 minutes hourly for even temperature distribution.
Different varieties are going to have different needs in terms of temperatures. For example, storage onions like Patterson can tolerate being in the fridge at 34°F, while sweet onions can tolerate 36°F. I personally have learned to separate the varieties for this reason. By storing them at their requested temperature, the shelf life of each type is maximized.
Read the full article: 7 Essential Signs for When to Harvest Onions
