Before you starting planning your garden and ordering seeds, you need to know your planting zones and frost dates! Here are a few resources to help you find yours.
Planting zones, otherwise known as plant hardiness zones, are areas on a map that are categorized by average climate. Determining your zone can help you figure out which plants, trees, shrubs etc. are likely to be able to survive through winter.
This is mostly important for perennial plants, but can also help you determine which plants need to be brought inside for winter etc.
Once you figure out your zone, it's also important to find out when your first and last frost dates are. This will determine when you should start your seeds indoors, when you can direct sow seeds, and when your garden season is most likely to end.
Let's dive into both of these topics a bit deeper.
What is a Planting Zone
Your planting zone is determined by the average climatic conditions of the area in which you live.
The Canadian map is divided into ten zones, where 0 represents the coldest zone, and 8 represents the warmest zone. Most of the zones also have sub zones a and b, where a is colder than b.
Although both maps use a similar naming convention, it's important to note that they are not measured using the same methods!
The USDA map is only based on average annual minimum temperatures, while the NRC map looks at seven climate variables, including maximum temperatures, maximum snow depth, and the length of frost-free periods.
That being said, the NRC does also have a second map that shows plant hardiness zones for Canada based on the USDA extreme minimum temperature approach, shown below.
This map was created because some plants are traded between the countries, and people in the horticultural industry sometimes need to be able to compare our minimum temperatures to the ones in the United States.
For Canadian home gardening purposes though, you'll want to refer to the first map.
Finding Your Planting Zone
If those maps look overwhelming to you, don't worry. There are really easy ways to find out the planting zone for your exact area.
Canadian Planting Zones
If you're living in Canada, you can visit the Natural Resources Canada website, use the drop down menu to sort by province, and then search for your town. Here you'll find 4 numbers listed for your municipality.
The first number is the 1961-1990 zone, this is the original zone for your area. Over time, the data collection methods and climates in each area have changed, so the second number is the updated 1981-2010 zone. Both zone numbers are published so that you can use them for reference, but you can ignore the last two numbers on that page for now.
USA Planting Zones
If you're living in the United States, you can go to the USDA Agricultural Research Service website and plug in your ZIP code to find your zone.
If you want to try to compare the NRC zones to the USDA zones, I've read that they can differ from half a zone up to 2 zones. But the general rule is you add 1 to the NRC zone. For example, a zone 6 in Canada would be a zone 7 in the United States. It's not 100% accurate, but at least it gives you an idea to start with.
Why Planting Zones Aren't 100% Accurate
It's important to note that your zone may not be completely accurate. Like the pirate code in the Pirates of the Caribbean film, they are meant to be used as guidelines, not rules.
If you live near a body of water, or a mountain, or get a lot of wind etc. you could be in a microclimate, and that will affect how your plants grow. Plus, there are lots of other factors that can affect whether or not a plant survives, like moisture, light and so on.
Most plant catalogues and websites highlight the hardiness zones that the plant will thrive in. When deciding on which plants to grow in your garden, choose plants that are rated for a zone that is hardier than yours.
For example, if a plant is hardy to zone 6, and you live in zone 7, that plant should survive. But if a plant is hardy to zone 8 (warmer than zone 7), it's not likely to do as well.
Why Knowing Your Zone Is Helpful
Here's an example of why knowing your zone can be useful:
One of my favourite garden content creators is Laura from Garden Answer. I enjoy her gardening videos the way that I assume some people enjoy reading Vogue magazine. The content is aspirational!
Anyhow, when I first found Laura's channel, I was excited because she lives in "Ontario"., and I thought her advice would be relevant to me. But eventually, I realized that her "Ontario" is Ontario, Oregon, while my "Ontario" is Ontario, Canada.
I was disappointed, but figured since her planting zone is similar to mine I could still follow her advice and expect similar results.
Her climate is actually much warmer than mine, and it seems like her planting season is longer too. So even though her number from the USDA map is similar to my number on the NRC map, they don't mean the same thing at all.
How to Find Your First and Last Frost Dates
Knowing your average last frost date is really important when it comes to Spring planting. Your last frost date is an estimate of when you'll have your last light freeze in spring.
A light freeze can kill tender plants, so you need to know when it will be safe to move seedlings or direct sow seeds in your garden.
Your average last frost date is an estimate of when you'll have your first light freeze in Autumn, which signals the end of your growing season.
Frost is predicted when the temperature in the air reaches 0°C (32°F). However, since the ground is often colder than the air above it, frost can occur on plants at temperatures just about freezing as well.
All frost dates are based on historical climate data for your region, and much like the planting zones, they are meant to be used as a guide. Be sure to check your local weather forecast for both daytime and nighttime temperatures to determine when it will actually be warm enough to start gardening, or cold enough to start closing your garden.
To find your frost dates in Canada or the United States, you can use this frost date calculator from The Old Farmer's Almanac. You can also find average frost dates for several Canadian cities on the Veseys website.
I hope you found this article useful! If you have any questions, please leave them in the comments below.