Protect Your Onions from a Freeze
Onions can withstand light to heavy frosts and moderate freezes, but hard freezes can result in onion damage. Covering the plants with a protective covering or tarp will greatly reduce freeze damage, especially if temperatures are dropping below 20˚F. We say that onion plants can survive temperatures as low as 20˚F, but what matters more is how long the temperatures are below freezing. Longer periods of freezing temperatures cause more damage to the plants.
The effect of freezing temperatures varies considering how many carbohydrates are available to the plant when the plant begins the recovery process following a freeze. If the plant uses up all of its carbohydrates that are stored in the bulb before it has the opportunity to regenerate more carbohydrates, the plant will die.
Take These Actions
A cultivation prior to a hard freeze results in a layer of moist soil at the surface that acts as insulation. This holds the day’s heat in the soil around the bulb and root. We also tell customers to water their plants in well prior to a freeze. This will also serve as insulation around the bulb.
The best thing you can do is to make sure the plant has everything it needs to get growing or generating more carbohydrates by supplying the plant with water and chemicals necessary to restore its health.
How to Tell If Your Onions Have Been Damaged
Freeze injury may be readily detectable as translucent or water soaked outer scales of the bulbs. One or two days after the freeze event, onions should be cut transversely to see if translucent scales are present.
If you see some new leaves emerging, your plant is on its way to recovery. This may take a couple of weeks. After a week or so, pull the plant out; if it becomes mush when you squeeze the bulb, your plants have not survived the freeze.