Frost Dates & Hardiness Zones
Collectively, the question I get asked the most often in the comments section is “what zone are you in?” New gardeners especially are desperately trying to understand what to do and when. The idea that everybody in the same zone can garden the same would make sense, right? Unfortunately it doesn’t work that way. Frost dates and USDA Hardiness Zones are probably some of the most misunderstood pieces of information in the gardening world. Making sense of that information and learning how to apply it is key to success in your garden.
So what are frost dates? They are dates based on historical data for your specific zip code, that predict the timing of frost. You need to know these dates for your location so you know when it’s safe to plant your frost-tender plants outside. You will have your last frost date in the spring where past that date, it’s unlikely you will have freezing temperatures anymore until your first frost date in the fall. After that first frost date, frost can happen regularly leading into winter. For me in Warrensburg, Missouri, my last frost date is April 23rd and my first frost date is October 16th. If you have Google count the days between those dates, that will give you the length of your frost-free growing season. I have 175 days here which is a pretty long season.
Let me stress again that frost dates a historical average for your zip code. It’s a guess, not a guarantee. In the spring as you approach your last frost date, start checking the 10-day forecast. Even beyond that date, in early spring you have to be prepared that you could have a late cold snap. I have years where my first frost date comes early but more often I don’t get frost until late October or even into November. Your specific property elevation, microclimates and ongoing weather systems can all cause variance in your actual frost dates. My best advice on the subject of frost dates is to talk with experienced gardeners in your areas. I learned from a wise Missouri gardener that even with a frost date in April, Mother’s Day is the point when it’s truly safe to plant my tomatoes outside. A cold snap after Mother’s day is very unlikely. I have found that different areas have different timing quirks like that.
So now that you understand frost dates, let’s break down zones. The United States Department of Agriculture compiled data to figure out how cold the coldest day gets in a specific place. That’s literally all that your zone tells you…. How cold the coldest cold is where you live at. The United States is divided into 12 zones to be exact. Zone 1 starts us off way up in the harshest regions of Alaska. Zone 12 is reserved for Puerto Rico and Hawaii. In central Missouri, I’m in Zone 6A. On average, I don’t typically get temperatures colder than -l0 degrees Fahrenheit.
So here is the thing I want to preach on a bit. When you are growing an annual vegetable garden, your zone really does not matter. You are not going to experience your coldest cold in the summertime when all of your tomatoes are planted. You see those temperatures in the middle of winter when it’s likely your garden is put to bed and resting. Your frost dates are much more important when growing annual vegetables than your zone.
It’s also important to note that frost dates do not coincide with zones at all. I looked up 10 zip code all in zone 6A. None of them have the same frost dates. None of them have the same growing season length. Let’s take Fox, Oregon for example. It is also in zone 6A just like me. But the last frost date there is June 14th and the first frost date is September 7th. That’s a growing season of only 84 days yet we’re the same zone. See what I’m getting at here? If somebody living in Fox, Oregon decided to plant what they see me planting online at the same time because we’re both in Zone 6A, they would probably struggle... But if they planned their garden based on their frost dates, they would probably be much more successful.
The only things that your zone really matters for are perennial plants and trees. Those will all go into dormancy over winter but some plants are cold hardier than others. All fruit and nut trees and berries even have a minimum number of chill hours they need to experience in order to produce fruit. Citrus however does not need chill hours. Citrus can’t handle extreme cold at all. Unless you are growing it in a container, citrus is only able to survive in zones 8-11. Going the other way, cherry trees really need cold. They can only be grown in zones 4-8 and will struggle to produce fruit below zone 8. Once you know my zone, you’ll be able to pick out trees and plants with confidence that they will thrive where you live.
Do you know your frost dates and your zone? If not, click the button below. There you’ll find resources to look up that information for exactly where you are gardening at.