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Will Frost Hurt Onion Plants? How To Protect?

It is a well-known fact that onion is one of the easy-to-grow plants in your garden. It eats up little space and has a short growing period; you could plant a bunch of them in your flower bed if space is the problem.

Onions are classified as cool-season crops and can tolerate light freezes. They have no fuss about their growing locations and thrive best when seeded during moderate temperatures.

Onions are hardy enough to be rarely destroyed by frost or freezing temperatures. They prefer fertile and well-drained soils.

Let us learn more about what temperature extremes they can tolerate and how to protect them.

can-onions-tolerate-frost

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Can Frost Hurt Onion Plants? 

Onions can tolerate a wide range of temperatures. Their roots, bulbs, and leaves develop best in a temperature range of 12-23 degrees celsius.

Additionally, a  temperature range of 20-25 degrees celsius favors optimal leaf growth. It can also easily withstand temperatures above 23 degrees celsius during bulb formation.

Onions tolerate frost depending on their age and the degree of coldness.

The young shoots are more vulnerable and need protection before the onset of a hard freeze.

Onion-sprouts

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The geographic location also plays a big role in determining their resilience. Gardeners living in the North or temperate West have to contend with prolonged sub-zero temperatures that could destroy their onions.

Prolonged freeze below -2 degrees celsius could indeed prove fatal. The low temperatures lead to the formation of ice crystals in the tissues.

However, a bit of cold isn’t bad for onions; a light frost wouldn’t hurt newly planted onions. 

Protecting Your Onions From Frost 

Protecting-onions

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If you expect a hard freeze, you want to cover your tiny plants for protection. To do this best, use organic mulch, preferably straw, pine needles, simple bark, or grass clippings, and ensure that the layer is at least two inches thick.

At springtime, get rid of the mulch as the ground begins to warm.

Alternatively, you could plant the onions indoors in a container and place the container close to the kitchen door.

You could also plant your onions in raised beds in a temperature-controlled environment if living in frigid climates.

How to Grow Onions?

As a home gardener, there are three options you could go for when planting onions. These include onion seeds, slips (seedlings), and bulbs.

Planting onions from seeds takes the longest time but gives you large bulbs that stay fresh for quite a long time.

On the other hand,  slips are hardier than seeds and give you a head start and more resilience.

Onions grown from bulbs mature faster but are prone to bolting and rot.

The best time to plant onions is in spring, when the soil dries out.

Alternatively, if you live in a temperate climate zone, you could plant onions in the fall for harvest during spring.

Avoid planting onions in freezing weather unless you do not want them to form bulbs.

Harvesting-onions

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 The best time to plant your onions is in late March or early April. Ensure to dig your soil a couple of months before planting and incorporate it with manure.

During planting,  plant your onions in shallow drills at a depth of half to 1 inch. Maintain a spacing of 10-15 centimeters within the plants and ensure the rows are 2-5 centimeters apart to create enough space for weeding.

Additionally, ensure that the soil is fertile, well-drained, and relatively moist to aid development.

Harvesting Onions 

Harvest your onions when the tops begin to yellow off and dry. They take approximately 150 days to reach maturity from planting seeds.

If you plant them from bulbs, you can harvest them after 100 days.

After harvesting, cure the bulbs for storage. Allow them to dry in a warm, dry area for two weeks or more.

Onion-bulbs

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Regarding storage, store them in a well-ventilated container similar to a mesh bag. You also have the option of wrapping onions in foils and storing them in a refrigerator. They stay fresh for 6-8 months this way.

Pungent onions stay longer than sweet onions due to low moisture content. 

Wrap Up 

Onions are cool-season plants that can survive a light frost. However, they can get damaged under low-temperature extremes.

Furthermore, temperatures below -2 degrees celsius are not conducive for the growth of the young shoots.

You can protect your onions by covering them with a 2-inch thick mulch material if you anticipate the occurrence of a hard freeze later in the season.

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