When I first started gardening, I’ll be honest, I didn’t know my plant hardiness zone. Unless you’ve been around fellow gardeners or have already done extensive research, it’s not really a topic you’d know when you first start gardening. And that’s perfectly fine. It’s also sometimes referred to as a hardiness zone, zone (in a gardening context), or planting zone. To fully appreciate plant hardiness zones, we’ll look at why they matter, the crops that are affected by them, and how you can learn about your hardiness zone along with tips for gardening.
Why Do Plant Hardiness Zones Matter?
We’ll get into the details of plant hardiness zones later on, but to begin with let’s start with a basic definition. Zones are regions with similar temperatures, specifically similar temperatures during the coldest days of the year. They call them the “average extreme minimum temperatures.” They’re categorized by numbers 1-13, cold to warm regions, and each number is broken into 2 subcategories “a” and “b.”
Once you know your plant hardiness zone it will help you with your gardening. Knowing your zone will help with picking the right crops and varieties for your location, when to plant, and researching what grows best for your climate.
Know What You Can Plant
Knowing your plant hardiness zone can help you decide what you can plant in your region. There is a lot of research out there, and once you know your zone, you can go to town Googling what grows in your zone.
For example, I live in zone 9b. If a plant I’m interested in growing has a tag (or information online) that says it’s hardy in zones 9-11 or any other range that includes zone 9, then that plant is hardy in my area and I should be able to grow it. There are additional factors that come into play like rain, humidity, and chill hours.
Knowing your plant hardiness zone will also help you figure out if some herbs and flowers you’re growing will be perennials or annuals. For example – Mexican Heather is an annual in all zones except zone 9 and warmer. That means I can grow Mexican heather as a perennial for multiple years. This can change if winter is exceptionally cold, or if *ahem* I forget to cover them during freezes. Hey, it happens to all of us.
Save Time and Money Buying The Right Varieties
When I first started growing my vegetable garden, before I had done any research, I purchased a few tomato seed packets. This was before I knew certain varieties to better in different areas. I live in a warm region, where a lot of vegetables can’t grow during our hottest summer months. I also happen to live somewhere that has a lot of humidity. These two factors have a lot of say with what varieties I can and can’t grow. Those first few seed packets I purchased? They didn’t do well. Had I known my location and what grew well in it, I could have saved a lot of time and money. One of the many reasons it’s good to start small and to know your zone.
Grow With a Plan
There’s nothing I love more than a good plan. And a chocolate chip cookie (which may or may not help with your planning). I personally love gardening with a plan, and I feel it has helped my garden tremendously. Once you know your plant hardiness zone, you can start doing a lot more planning for your garden. Planning what you want to grow and when will help you have a more successful garden. You can also take into consideration how you’re going to deal with your unique temperatures. Having your own dedicated garden planner can help you to stay organized and collect your thoughts.
Warm- and Cool-Season Crops
Did you know that there are both warm- and cool-season crops? Vegetables fall into one of two categories, which basically tell us if they’ll be able to survive cooler temperatures. They can be broken out further to show light freeze vs hard freeze vegetables which you can check out here. All other plants have their own temperature tolerances as well – trees, bushes, herbs, and flowers.
Warm Season Vegetables
In locations with 4 distinct seasons, warm-season vegetables would be your spring and summer vegetables. Down in Florida, the majority of warm-season vegetables grow well during the spring and fall. These crops are much more sensitive to cold weather and don’t survive freezing temperatures. This means when temperatures go below 40 degrees Fahrenheit, I cover my plants with frost blankets. It also means I try to plan my warm-season crops so that they’ll be harvested before the average first frost in my area. The following is a list of warm-season vegetables.
Warm-season vegetables: beans, corn, cucumbers, eggplant, melons, peppers, zucchini and summer squash, pumpkin and winter squash, sweet potato, tomato, and watermelon.
Cool Season Vegetables
Cool-season vegetables thrive in cooler temperatures and actually taste better when temperatures are low. If you try to grow these vegetables when it’s warm out they can taste bitter and bolt (which means they start producing seeds to flower). If you live in the south this means you have a limited season where you can grow cool-season vegetables, while regions further north can grow more varieties of cool-season vegetables, and for longer periods of time. The following is a list of cool-season vegetables.
Cool-season vegetables: asparagus, beets, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, celery, Chinese cabbage, collard greens, endive, Swiss chard, kale, kohlrabi, leek, lettuce, mustard greens, onion, parsnips, peas, Irish potatoes, radishes, rhubarb, shallots, spinach, and turnips.
Zones that have lower temperatures generally have longer cool seasons, and therefore, more chill hours. But you’ll have to do some research to find out how many your area gets. Chill hours are classically known as any hours where temperatures fall below 45°F (though there are different theories on specific low-temperature ranges). Chill hours are important to know especially when growing fruit trees. Fruit trees require a certain number of chill hours to blossom and produce fruit.
For example, most European pears do well in zones 5-8 and require somewhere between 500 to 800 chill hours. On the other hand, Asian pears do well in zones 5-10, but only need 250-400 hours, depending on the variety. So while both can be grown in zone 5 in theory, European pears need a lot more time exposed to cooler temperatures.
My favorite apple, Honey Crisp, requires 1000 chill hours. My second favorite, Pink Lady, only requires 400.
Citrus and other tropical trees, on the other hand, don’t need chill hours and get unhappy when temperatures drop to 32 degrees.
GrowOrganic.com is one of many places that ship trees. What I love about their interface is that it includes an option on the lefthand side to select the zone you’re in for their fruit trees – check it out: Grow Organic Fruit Trees. They also have a page that explains chill hours in more detail.
The Midwestern Regional Climate Center offers a national map that provides chill hours across the country. You can check out their current map for this year starting on September 1st.
Plant Hardiness Zones
Knowing your plant hardiness zone is one of those gardening cornerstones of knowledge. Once you know your plant hardiness zone you’ll be able to learn more about what grows in your area and how to grow a successful garden. And a successful garden is when you’re learning and having fun!
Find Your Plant Hardiness Zone
The Plant Hardiness Zone Map is separated into regions, or zones, that are numbered 1 to 13. Each numbered zone is then broken down into an “a” and “b” category. Each numbered zone represents a 10-degree change in average temperature lows. And each letter breaks the temperature gap down to 5-degree changes.
For example, Zone 8 has average lows ranging from 10 to 20 degrees Fahrenheit. Zone 9 has average lows ranging from 20 to 30 degrees Fahrenheit. Zone 9a average lows range from 20 to 25 degrees Fahrenheit, while Zone 9b average lows range from 25 to 30 degrees Fahrenheit.
To verify your planting zone you can check out the USDA Map. Enter your zip code on their site, or check out the picture below from their site.
Know Your First and Last Frost Dates
I signed up for my county’s weather alerts during Hurricane Irma, so I actually get texts now if there’s a freeze warning for my area. Whatever your method is – TV, app, computer – start watching when you get close to your cool weather transition based on your planting zone.
Here’s a quick guide that shows when the average first and last freeze dates are for your planting zone. These are pretty generalized since planting zones cover a wide area, but they can give you a ballpark idea.
First and Last Frost Dates Averages by Hardiness Zone
|USDA Hardiness Zone||Average First Frost Date||Average Last Frost Date|
|1||Aug 1||Jun 15|
|2||Aug 30||Jun 15|
|3||Sep 15||Jun 15|
|4||Oct 1||Jun 1|
|5||Oct 15||May 15|
|6||Nov 1||May 1|
|7||Nov 15||Apr 15|
|8||Dec 1||Apr 1|
|9||Dec 15||Mar 1|
|10||Dec 15||Feb 1|
|11-13||No Frost||No Frost|
You can also use the Farmer’s Almanac to look up your average first and last frost dates based on zip code. But again, every year is going to vary, and paying attention to your local news will be the best way to prepare.
How You Can Plan
As mentioned earlier, knowing your plant hardiness zone is a cornerstone for building your garden’s success. Once you know your zone you can start building on top of that. You can select the appropriate plants, plan your garden, and prepare accordingly for the seasons and temperatures that you will be experiencing in your zone.
Select the Right Crops for Your Zone
Once you know your plant hardiness zone you can start selecting crops, and varieties of crops, that are appropriate for your region. To learn about what grows best in your unique area, you can look up your local Cooperative Extension Office. If you’re located in Central Florida, you can check out our Central Florida Planting Guides. While your growing zone will play a considerable role in what you can grow, other factors like chill hours and humidity levels will also influence what you can grow. Because of this, your local extension office should have more accurate information than just looking at your plant hardiness zone.
Prepare for Hot and Cold Months
Knowing your plant hardiness zone will help you to know how cold it gets where you live, and if it gets cold enough for some plants. If you live in a zone that gets average low temperatures that are freezing, then you’ll want to invest in a few frost blankets. And you’ll want to know how to protect your plants from the cold. If you live in a southern state or another area that gets exceptionally hot, you may want a few shade cloths. And you’ll want to know how to shield your plants from some of the heat. We can’t change the climate of our location (unless we move), but we can learn how to adapt by growing plants that prefer our climates, and finding ways to make temperatures have less of an extreme impact on our gardens.
Write Down Your First and Last Frost Dates
Plant hardiness zones and regions are helpful for general guidelines. The person who lives out in the country and in the northernmost area of zone 7 is going to experience something different than someone in the suburbs of the southernmost area of zone 7. Do you live near a lake? Are there a lot of trees to block the wind? There are so many factors that the best way, in my opinion, to know more about your specific location is to keep garden notes. Record your first and last frost dates, along with the highs and lows. Record what you use to protect your garden and the varieties of vegetables you grow. And record what works and what doesn’t. That way the next year, and the year after that, you’ll continue to become more successful at growing. I’m a huge believer in keeping a garden planner and writing things down.
Do you know your plant hardiness zone? Comment below your zone!