New USDA Plant Hardiness Zone Map for 2023: What It Means for Vegetable Gardeners

The United States Department of Agriculture (USDA) recently released the updated 2023 version of the Plant Hardiness Zone Map. This map provides useful insights into the minimum temperatures experienced across different regions of the country. Not surprisingly, the latest data shows a trend toward warmer minimum temperatures, which carries implications for vegetable gardeners nationwide.

Today I’d like to explain the practical impact these changes will have on those of us who grow edibles in the U.S. But first, some basics.

Understanding the Zone Map

The USDA Plant Hardiness Zone Map is an instructional tool for gardeners, helping us to understand the lower limits of our growing seasons.

The map divides the U.S. into 13 zones of 10 degrees each, based on the average annual minimum winter temperature, with Zone 1 being the coldest and Zone 13 the hottest. Each zone is further subdivided into 5-degree half zones of A and B, for a total of 26. The official map is color-coded for easy visual reference:

How does the map help gardeners? When researching plants to grow in your area, some seed producers include Zone information on their seed packets (or perhaps in the product descriptions of their websites), although this is falling out of practice in favor of more specific growing season information.

Because, being perfectly honest about it, knowing your coldest winter temperature isn’t the best indicator for plant selection, since most of our favorite vegetables can’t survive frost or snowfall. The majority of the U.S. is considered temperate, so it doesn’t matter whether the lowest temperature is 32ºF or -10ºF: Tomatoes won’t grow outdoors year-round in temperate zones.

The more important temperature statistics are the last spring and first autumn frost dates of the year because these dates determine what vegetable varieties will have time to grow and mature within temperatures they can tolerate and thrive in. Generally speaking, frost hardiness is more important than low-winter-temperature hardiness. Learn more about frost dates.

However, the Zone Map — particularly over time — is an interesting tool to monitor temperature changes across the U.S. And, of course, when a gardener moves to a new location, it’s a helpful resource to get a foundational understanding of the severity of winter weather in their new location. For example, moving from Maine to the southern tip of Florida means you can just about grow tomatoes year-round!

Download your own copy of the official map in PDF format. Or try the interactive map, where you can input your street address and get a close-up view of your zone and the areas around you.

What’s changed with the new map?

The USDA Plant Hardiness Zone Maps are updated infrequently: The previous map was from 2012, and before that 1990, so there’s a significant span of time for data collection and analysis.

Temperature is data collected from weather stations across the United States. The 2023 map used 13,625 whereas the 2012 used 7,983 — a significant increase that provides far more localized data points.

In general, the 2023 map shows that most regions of the U.S. experienced an approximate one-quarter shift upwards in minimum winter temperatures. This warming trend can be attributed to a variety of factors, including climate change, more weather station data points, and improved data interpolation on the part of the mapmakers.

But what does this mean?

I’ve definitely noticed the warming trend in my area — which I’ll discuss further below — but its impact has been less about what I grow than how I must now manage vegetable gardens. But first, let’s consider the ways that changes in temperature affect gardening in general:

1. Extended Growing Seasons: Warmer minimum temperatures may mean longer growing seasons for vegetables. Gardeners in areas that have shifted to a milder zone might be able to enjoy an extended period for planting and harvesting their crops.
2. Expanded Plant Choices: With the changing climate, gardeners may have the opportunity to experiment with a wider variety of vegetables that were previously considered too sensitive to cold temperatures, meaning more diverse and interesting vegetable options.
3. Pest and Disease Challenges: Warmer temperatures may also bring new challenges in the form of increased pest and disease pressures. Gardeners may need to adapt their pest management strategies to protect their crops effectively.
4. Water Management: As temperatures rise, water management becomes more of an issue. Gardeners should be prepared for potential changes in rainfall patterns and consider water-efficient gardening techniques, such as using ollas.
5. Zone Selection: Gardeners should revisit their local hardiness zone and adjust their plant selections accordingly. Consult the updated map to ensure that the chosen vegetables are still well-suited to the current climate conditions in your area.

Impact in the Ohio Valley — My Perspective

I’d also like to take a moment to discuss the practical implications of this warming trend by using my own observations over 35 years of gardening in the same location, and noting some of the growing season changes here in southwestern Ohio. So, while my region might not match up with yours, the general trend might apply.

Here’s a comparison of the 2012 zone map with the 2023 for my tri-state area of Ohio, Kentucky, and Indiana:

For quick visual reference, the blue 5b and dark green 6a areas are the coldest, progressing through warmer light green 6b and olive green 7a.

You can see that in 2012, most of Ohio fell within zone 6a. But by 2023, all of the coldest 5b blue areas had disappeared, and the still-cold 6a dark green areas had retreated.

I live along the Ohio-Kentucky border as part of the Greater Cincinnati area (denoted by the small gold stars), and in 2012, I was considered zone 6b: Most of Kentucky was in zone 6b, and it stretched for a short span across the Ohio River into Ohio.

In fact, the dividing line between zones 6a and 6b was literally just a couple of miles down the street from me.

But now in 2023, all of southern Ohio is solidly in zones 6b or 7a, the blue 5b zone in Indiana has all but retreated, and most of Kentucky is now in zone 7a.

Now, this warming trend doesn’t mean that I can suddenly grow tropical plants in my backyard. My roster of herbs and vegetable families actually remains unchanged. But there has been an impact as far as when I plant, when I harvest, and when I halt a crop (i.e., by removing the plants). Let’s go through it point by point, using the first four items from impact list in the previous section.

Extended Growing Seasons

This has been one of the most noticeable impacts of the warming trend in my zone. I haven’t gained time in the spring — unfortunately, lol — because we’re still subject to killing frosts and accumulating snow as late as mid-April. So, no early starts here, sadly. But it’s definitely warmer, longer in the fall, with delayed first frosts and first snowfalls.

In decades past, September frosts used to reliably halt tomato production, and my tomato garden would be completely finished, torn down, and the beds turned over by early October. For the last few years, warm temperatures — often in the 90s — mean that my tomato gardens continue producing through October. In fact, in 2023, I didn’t remove my tomato plants until early November … and they were still loaded with green tomatoes.

Another clear impact of the long, warm fall is planting garlic for the next season. The goal is to sow garlic cloves just before the first hard frost. In years past, that happened in mid-October at the latest. Now, it’s mid-late November.

Although my garlic is already in the ground here on November 24, 2023, I could easily have waited until next week, as we have yet to experience either a ground-freezing frost or a snowfall this season.

Expanded Plant Choices

As I said earlier, I still can’t grow tropical fruits or vegetables here, but the longer fall means that I can take on crops that have long maturing seasons, and need that extra warm weather time in the fall to reach harvest. For me, that means growing more peppers and chiles.

In the past, my slow-growing poblanos would struggle to ripen half of the crop by the first frost in September. Frustrating, to be sure. But now, I get the full season’s production — an abundance of big, beautiful peppers — in October.

This applies to other favorites, too, such as my biquinho peppers, which are slow growing at all stages, including — maddeningly, lol — ripening.

Another example for some of you will be leeks. I grow leeks and leave some in the garden over the winter for cooking. Leeks hold extremely well in cold weather, with the only challenge getting them out of the frozen ground.

If you live in an area that now experiences less ground freezing, you can overwinter leeks, and you’ll be able to dig them up with ease.

On the downside, the warming trend has affected my ability to have a long-lasting cilantro crop (one of my favorite herbs). Cilantro is a cool-weather herb and most varieties will immediately bolt at the first stretch of heat. Which, unfortunately, has been occurring for the last several years in May: Memorial Day weekend has a freak streak of 90ºFs, and then falls back down to normal temperatures.

But however brief, it’s enough to kick the cilantro plant into seed-producing gear. (Planting them in containers and bringing them inside for a few days usually does the trick, but no more luscious beds of cilantro outdoors.)

Pest and Disease Challenges

Oh, boy. This is the biggie. Not so much diseases for me, but pests. The last several winters have not had a sustained cold to where it kills off certain insects. So by April, many are out in full force.

This year, my entire neighborhood had a crazy huge problem with wasps and hornets. Nearly every yard had a Bald-Faced Hornet’s infamous papier-mâché nest in one tree or other. They’re super-aggressive and there were many incidents of serious stinging attacks, especially at the parks. Same with ground hornets. It was a very bad year for angry things with stingers.

But the warmer weather impacts other, more friendly pollinators, too. The honeybees and bumbles were out so early this year (2023) that it was actually just heartbreaking. There was nothing for them to collect pollen from, as it was still weeks before the first blooming trees — and even dandelions — would do their thing.

And I can’t go without mentioning stink bugs. They’re always a problem, but this year was a banner year: They were up and about early and stayed a long time.

In general, all the usual suspects in my garden — aphids, cabbage worms, cucumber beetles, squash beetles — were up and running with the first sustained stretch of heat. In the past, they would start showing up sometime in late June or early July.

Water Management

The warmer weather definitely impacts water requirements. Especially for my container garden, which gets thirstier more quickly under the blazing sun than plants in the ground.

The frequency of anti-stress watering — my term for having to water a plant off-schedule because the heat of the day has prematurely dried out the soil and the plant is stressed and droopy — has increased. (For reference, I don’t have an irrigation system set up in my gardens. I water by hand in the morning.)

This kind of emergency watering used to only happen in July and August, when we would occasionally hit the 90ºs and 100ºs. But now anti-stress watering is necessary from the end of May to the end of September.

The new zone map isn’t telling me anything that I haven’t already observed in my own gardens, but it’s very interesting to note how widespread these changes are. Be sure to check it out!