Here is the BEST Time to Plant Onions in Illinois (2022)

Do you want to grow onions in Illinois, but don’t know when to plant them?

Planting onions is not as easy as it seems.

Here’s why:

  • Onions are not able to survive frost or cold weather under 50 degrees Fahrenheit.

So if you plant them outside too early in the spring they will die. And if you plant them too late, your onions won’t produce a harvest before the first frost arrives in the fall.

Today, I’m going to teach you the ideal time to plant onions in Illinois:

  • To Learn More About HOW to Grow Onions, Check Out This GUIDE!


When to Plant Onions in Illinois

As you may have already guessed, you need to pay very close attention to your local weather in the spring. Specifically, you are going to need to watch when the last frost occurs.

In general, when there hasn’t been a frost for two weeks, you are SAFE to plant your onions outside in Illinois!

For your reference, I have created this table for average frost dates for most major cities in Illinois. If your city is not listed below you can find its Last & First Frost Dates HERE.

Illinois Last & First Frost Dates

Illinois Frost Dates

Unfortunately, Mother Nature plays cruel tricks on us every year.

It should be noted that the above dates are just averages.

There are years when the last frost comes MUCH later. Sometimes, the last frost happens much earlier and you can get your onions planted outside in Illinois much quicker.

Like I said before, you need to be very diligent in checking your local weather.

So what happens if a frost comes AFTER you plant your onions?

When you know a frost is coming you need to take action.

  • If onions are in pots, bring them inside
  • If onions are in the ground, cover them in burlap and hope they survive

Also, make sure not to plant your onions in your garden too late.

  • Planting onions too late will cause small onions or even worse, no onions.


When Should You Start Your Onions Seeds Indoors?

Depending on the type of onions, it takes roughly 60-70 days to grow onions from seed indoors and then transplant them to your garden.

For a specific date that you should start onions seeds indoors you should:

  • Find the last average frost date HERE
  • And then subtract 70 days from it

Not only this, but I recommend again paying close attention to your local weather report.

It should also be noted that the best technique for bringing your onions plants outside is to introduce them (in their pots) outside for an hour. And then increase the amount of time they spend outside each day by an hour until they have been outside for 8 hours.

This will “hardened” your onions plant, increasing its chances of fighting off diseases, insects, droughts, and wet conditions.

If you want to learn WHEN to plant ANY Vegetable in Illinois, head over to HERE and just type in the vegetable you want to grow.

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