Your First Fall Frost Guide: The When, What, Why & How
If you’re new to gardening the term “frost date” might be completely foreign. But if you’re a seasoned gardener then it’s a term that’s top of mind as soon as Fall rolls around. This is because that first Fall frost can change everything in your garden! So understanding not only when to expect it but how to prepare and even avoid getting hit is key. This first fall frost guide covers all that and more!
This post covers:
- What Are First Frost Dates
- Are Frost Dates Actually Accurate
- What’s The Difference Between Freeze, Frost and Hard Frost
- What’s The Difference Between A Light Freeze, Moderate Freeze and Severe Freeze
- Is It Important To Know Your First Frost Date
- How Do You Know When Frost Is Coming
- How To Calculate Your First Fall Frost Date
- Estimated First Frost Dates For Places In Canada
- Estimated First Frost Dates For Places In Northern U.S.
What Are First Frost Dates
The term first frost date refers to the average calendar date when the temperature in your region first drops to 0°C/32°F in the Fall. This causes frost to form.
This date varies greatly depending on your grow zone and even the microclimate in your own backyard. For example, here in my Zone 3 garden in Manitoba, Canada my average first frost date is typically September 22. This date is according to data from Natural Resources Canada Plant Hardiness Zones.
However in recent years we’ve had our first frost much later into mid October.
Here’s a simple way to think of your first frost date. Consider it the calendar date when the temperature first drops to 0°C/32°F in your own garden.
Remember, your first frost can be unique to the microclimate in your own backyard.
It might even vary from the first frost your neighbour experiences based on things like;
- The direction your garden faces
- The protection is has from wind
- Whether your plants are in the ground vs. containers
Are Frost Dates Actually Accurate
I love this question! And believe it’s important to discuss.
For years, gardeners and farmers have been following the frost dates laid out by national weather data to help determine when to plant, harvest and protect crops.
And while frost dates do serve a useful purpose it’s important to remember that they should only be considered a guide.
It’s said that there is typically a 33% probability each year that average frost dates will be accurate. And personally, I have found that more often then not I experience my first Fall frost much later than what the average is.
Additionally, our climate is changing so rapidly that the American and Canadian Plant Hardiness Zones should be updated annually to reflect the changes.
However, they’re not. In fact, the last time Natural Resources Canada updated this chart was in 2014! They have stated they plan to make changes in 2024 but they are yet to be released.
So, yes. It’s important to know when your average first frost is set to be for your region. But it’s even more important to take your own notes and record your own data.
What’s The Difference Between Freeze, Frost and Hard Frost
Going a step deeper into frost dates, there’s three terms you might hear and will want to familiarize yourself with further.
The first term is the “first freeze.” This refers to what we just covered, which is that first calendar date when the temperature drops to 0°C/32°F for the first time.
The first freeze will kill off tender plants that are directly exposed and uncovered.
The second term is “frost” or sometimes called “soft freeze.” Gardeners use this term to ultimately describe dew on plants that forms into frozen water droplets.
Frost won’t necessarily kill tender plants but it will definitely affect the rest of your gardening season. It can be especially impactful for conventional farmers who are harvesting.
And lastly the final term is “hard frost.” This term is typically used when temperatures dip below freezing for an extended period of time, killing most tender crops.
Usually, a hard frost signifies the official end of the gardening season as a whole (boo hoo). Of course, you can still grow frost-tolerant crops such as brassicas, salad greens and root vegetables.
What’s The Difference Between A Light Freeze, Moderate Freeze and Severe Freeze
Alright, let’s dive even deeper into these terms and break down the different types of freeze!
Why is this important to know?
Well it can help you better understand what types of plants will be cold-tolerant to the various levels of freeze.
Okay, let’s go!
What’s considered a light freeze?
First, a light freeze is classified as -1.7° to 0°C (29° to 32°F). This is when tender plants are killed.
Salad greens, brassicas and some perennial and annual flowers are all cold tolerant to a light freeze.
What’s considered a moderate freeze?
Next is a moderate freeze, which we classify as -3.9° to -2.2°C (25° to 28°F). This typically kills most plants that are uncovered.
Root crops and any bulbs that you’ve planted like garlic and tulips won’t be impacted.
What’s considered a severe freeze?
And finally we have a severe freeze, -5°C (24°F) and colder.
While many perennials can survive Winter temperatures like this, they will go into a dormant state. So it’s safe to say that a severe freeze will damage most plants.
Why It’s Important To Know Your First Frost Date As A Northern Gardener
As a Northern gardener, it’s SO key to understand when your first frost date is set to happen for a few reasons!
First, anticipating that first frost will allow you to protect tender plants and hopefully help them survive it.
Does The First Frost Mean Gardening Season Is Over?
No! Just because the first frost has arrived doesn’t necessarily mean freezing temps will continuously follow.
Because often Fall temperatures sky rocket again, and you’ll get a second push of the gardening season. This I always welcome with open arms!
Still, be sure to check your local weather forecast regularly during Fall so you can watch for when that first freeze is predicated to occur. .
Knowing Your First Frost Date Helps With Planning
Secondly, knowing your expected first frost date as a Northern gardener allows you to extend your season even further.
One way I extend my season is by covering tender crops with a heavy-weight row cover. This can actually protect crops down to -5°C/23°F.
You can simplify this process by even using heavy blankets and sheets that you already have at home. Of course, a backyard greenhouse like we have is another fantastic way to extend the season but a DIY cold frame will do the trick too!
Use Your First Fall Frost To Time Out Seed Starting
Thirdly, Northern gardeners will want to know when the first average frost date is as it will determine when you start seeds indoors.
For effective seed starting, count back from your last frost in the Spring until your first frost in the Fall.
Then choose to grow varieties that mature within that time frame.
Here’s a few more seed starting resources you might find helpful:
- Why Seed Starting: 10+ Reasons To Fall In Love With It
- Answers To Your 25 Most Asked Seed Starting Questions
- The Ultimate Seed Starting Guide For Canadian Gardeners
So all in all, if you live in a Northern gardening climate you should familiarize yourself with your first Fall frost date. It will hands down help you have more success in the garden!
How Do You Know When Frost Is Coming
Believe it or not, there’s a few signs you can look for that will indicate your first frost is coming.
Without doubt, the easiest way, and probably the most obvious, is to check your local forecast. Look to see when nighttime lows are set to dip to 0°C/32°F or colder.
Alternatively, you could go the “old school” way. Pay attention to the air temperature and morning dew.
Scientists claim if there’s no wind and dry air frost is less likely to form even if the temperatures dip to freezing.
Whereas if there’s light wind and more moisture in the air a frost can occur even without temperatures going down to 0°C/32°F.
How To Calculate Your First Fall Frost Date
There’s a helpful and free online tool you can use to calculate when your first frost date will be, which I will link here next!
Generally, the most effective way to understand when your first frost date will be for your garden is to;
- Pay attention to your local weather forecast
- Take notes year over year
- Record data on the microclimate in your own backyard
Now, here’s a great tool I like to use to find average first frost dates across Canada & the U.S.
The Farmer’s Almanac Frost Date Finder – it’s so easy to use and free! Just enter your postal/zip code and it will populate
Estimated First Frost Dates For Places In Canada
Let’s break down some general first frost date ranges for key northern gardening regions in Canada.
Average First Frost Dates In Yukon and Northwest Territories:
These far northern regions experience their first frosts as early as mid to late August. It’s critical to plant cold-hardy vegetables and short-season crops if you live up North!
Average First Frost Dates In Northern British Columbia and Alberta:
Frosts typically occur between late August and early September across northern B.C. and Alberta. Gardeners here can plant frost-resistant crops such as kale, spinach, and carrots to extend their season.
Average First Frost Dates In Northern Ontario and Quebec:
Frost dates usually fall between late September and early October in Ontario and Quebec. Beets, parsnips, and potatoes tend to thrive in these cooler temperatures.
Here’s a few average first frost dates for major cities across Canada. This is based on data from The Farmer’s Almanac Frost Date Finder:
- Vancouver First Fall Frost — October 19
- Kelowna First Fall Frost — October 6
- Edmonton First Fall Frost — September 16
- Calgary First Fall Frost — September 6
- Saskatoon First Fall Frost — September 19
- Regina First Fall Frost — September 1
- Winnipeg First Fall Frost — September 15
- The Pas First Fall Frost — September 10
- Thunder Bay First Fall Frost — September 9
- Toronto First Fall Frost — October 13
- Ottawa First Fall Frost — September 26
- Montreal First Fall Frost — October 11
- Fredericton First Fall Frost — September 25
- Halifax First Fall Frost — October 20
- Charlottetown First Fall Frost — October 20
- St.John’s First Fall Frost — October 20
Estimated First Frost Dates For Places In Northern U.S.
Now here’s an idea of the general first frost date ranges for northern gardening regions in the United States.
Average First Frost Dates In Northern New England (Maine, Vermont, New Hampshire):
These gardeners expect frost from late September to early October. Cold-season crops like broccoli and brussels sprouts are ideal.
Average First Frost Dates In Minnesota, North Dakota, and Montana:
These northern states often see their first frost in mid-to-late September. Growers should consider fast-maturing varieties and perennials suited to cold climates.
Average First Frost Dates In Pacific Northwest (Northern Washington and Oregon):
First frost typically arrives in mid-to-late October, giving gardeners a slightly longer growing season. Root vegetables and late-season greens perform well into the Fall.
Here’s a few average first frost dates for major areas across the Northern U.S. This is based on data from The Farmer’s Almanac Frost Date Finder:
- Spokane First Fall Frost — October 7
- Helena First Fall Frost — September 25
- Grand Forks First Fall Frost — September 26
- Fargo First Fall Frost — September 26
- Minneapolis First Fall Frost — October 10
- Rochester First Fall Frost — October 18
- Chicago First Fall Frost — November 1
- Milwaukee First Fall Frost — October 24
- Detroit First Fall Frost — October 25
- Buffalo First Fall Frost — October 11
And there you have it!
That covers (hopefully) everything you need to know about frost dates in the Fall! I hope this post answered some key questions for you.
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Good luck with your first Fall frost, gardeners!