Gardeners all over America- rejoice! Your time is here. For the first time since 2012, there is a new USDA plant hardiness zone map! 2023 brings a brand-new update to the respectable guide, and everyone interested in planting in tune with their climate deserves to know.
Here’s everything you need to know about USDA maps and why an update is a pretty big deal. Tune in.
What Are Plant Zones?
Plant hardiness zone designations represent the “average annual extreme minimum temperature” over the last 30 years. What does that mean? Well, it means that the lowest temperature of a location every year for 30 years is recorded and then averaged out over 30 years. In other words, it’s the worst temperature you can expect your plants to experience over the winter.
USDA Plant Hardiness Zone Map
The first ever US map with only 8 hardiness zones was compiled in 1927 by Dr. Alfred Rehder, based on plants and their survivability in different areas of America, and it didn’t belong to the government! It belonged to the Arnold Arboretum, which would continue this tradition until 1971. The first official USDA map was compiled in 1960, based on data from 450 weather stations around the country. Today, the map is incredibly more detailed, with a whopping 13,412 weather stations involved!
USDA Plant Hardiness Map’s Uses
By knowing the average annual extreme minimum temperature of their local climates (but never saying it five times fast!) gardeners, farmers and botanists alike have all been able to know precisely which plants can survive the winter in a given region. Remember, plants can be very sensitive, and one degree can make all the difference! Just a glance at this map can tell you loads about your country’s biogeography. Check it out!
Frequent & Other Users
The biggest fanbase of the USDA plant hardiness zone map is definitely the gardeners of America—congratulations if that includes you!! By being able to tell which perennial plants are most likely to thrive at a given location, hobbyist gardeners and professionals alike are able to cultivate magnificent ecosystems.
This map isn’t just for gardeners and farmers, of course. The USDA’s Risk Management Agency uses the plant hardiness zone map to set crop insurance standards for different regions. Scientists also use this data to show which insects, weeds and diseases may spread in an area. Microbes are temperature-sensitive, too!
So, When Do I Use a Plant Hardiness Map?
This is one handy tool to store in your garden-shed! Metaphorically, of course.
- When selecting perennial plants to grow in your garden
- When advising friends and family from afar on their gardening choices
- When seeking to understand the biology of plants observed outside of the home, or on the road!
- When looking to predict pests that might plague you or another in a certain location.
What Gardening Zone Do I Live in?
Using the Plant Hardiness Zone Maps (PHZM) with the data from 1974 to 1986 is surprisingly easy. Since they are based on the average extreme winter temperature, the first zone is the coldest and the last (13th) – the warmest. To make the distinction more precise, each zone also is divided into a and b. The maps are also colored to help tell apart the cold-hardiness zones in the USA and Puerto Rico.
The new map also features colors and 26 distinct zones. Each zone is in a range of 5 Fahrenheit and provides updated info collected more recently. A PRISM algorithm used in the making of new maps is much more precise, especially for mountainous areas. So grab a new, interactive, and downloadable USDA map and check your zone (and attributed color). Simply enter your ZIP code in the search code and find out which Plant Hardiness zone you belong to. New maps let you play around with controls, too, by using a special layers widget to adjust the preferable view.
How to Use the USDA Maps for Plant Growing
When growing any perennial plants, it’s absolutely crucial you use the Plant Hardiness Zone Maps to determine if your plant is safe and happy at the chosen location, although the map can’t predict the exact temperature fluctuations. However, these maps paired with botanists and other plant experts significantly raise the chances of your plants’ well-being.
Here are some factors that need to be taken into account when growing your perennials, recommended by the official USDA website:
Temperature
This is where the maps prove invaluable! It’s best to determine the overall zone you happen to be in advance and check in with the specific requirements of the plant species you are cultivating. Keep in mind, however, that there are often optimal, narrow ranges of temperature that the plants may prefer.
Light
Some plants are sun worshippers, the others – shade dwellers. When planting, always check what side of the world is your greenie's bright side, metaphorically speaking.
Cold Exposure Duration
Although it might be true that one temperature pitfall will probably not kill your plant, it is the prolonged exposure that is the danger. There is usually an approximate minimum temperature that the plant can tolerate (check PlantIn to find it out!), but there is also an amount of time that the plant can be exposed to cold weather before it inevitably decays.
Humidity and Soil Moisture
Those in cold regions with high humidity levels may find it easier to preserve their plants, in particular, evergreens. When the air is dry, it becomes a challenge for vegetation to hold on to precious moisture levels. However, moisture can be a tricky pal too, especially when it comes to soil. Some plants don’t like to get their feet wet in the ground and can have it hard through seasonal change.
USDA Plant Hardiness Zone Map Update in 2023
USDA updates are always big news for all American gardeners but the 2023 update really made quite a splash! As the temperature all over the world rises, the zones shift. But wait! Even though it might look that your zone has shifted significantly, USDA maps are based on temperature extremes. Don’t rush to replanting — there always needs to be a more detailed expertise prior to any of your big gardening changes.
The new version of the maps is not only surprising in terms of new plant choices (Maple trees in Minnesota!), it’s also, well… Better. Needless to say, USDA’s Agricultural Research Service (ARS) and Oregon State University’s (OSU) PRISM Climate Group are powerful allies to have when aiming for accuracy. Data from weather stations used has increased in size almost by a double compared to the previous USDA report. What’s even more important, the maps are interactive, downloadable, and easy to understand even for novice gardeners!
Why Was This Update Needed?
The first take is obvious: Global warming is a worrying sign of our times, and as the rising temperatures come, so do new gardening options. Yes, this means that you might be eligible to cultivate tangerines in your area! For the climate it’s, however, grim news.
However, Dr. Daly, the director of the PRISM Climate Group at Oregon State University warns against making global warming the culprit. Changes happen overtime, and the map is a representation of the average temperature cut in 30 years, so with ever more weather stations and tools available, the results are complex in nature.
States with Greatest Changes in Gardening Zones
Professor and Climatologist Christopher Daly claims that the greatest warming occurred in the central plains and midwestern areas of the United States. Notably, this includes Arkansas, Kentucky, Missouri and Tennessee, where temperatures have increased up to 5 degrees Fahrenheit.
Business Insider also highlights the exceptional case of Omaha, Nebraska, which shifted from 5b to 6a, a temperature differential of a whopping 15 degrees F (8.3 degrees C). This is made all the more stunning by its previous categorization in zone 4 in the 70s, representing a 25 degree F shift (14 degrees C). Furthermore, East Texas is broadening the borders into the west/southwest. Cary Sims in East Texas News, however, warns against trusting the Hardiness zones too much, finding rainfall levels, normally hovering around 50 inches, an important missed-out factor.
Pitfalls of this Planting Zone Map
Although the 2023-updated USDA plant zone map shows a great increase in precision of data compared to its 2012 or earlier ancestors, there are climatological factors that escape its description. These limitations include:
This map considers average annual extreme minimum temperature; only. This means that factors such as humidity, length of growing season, or soil quality are not reflected in this map.
The zones given by the map fail to describe the particularities of microclimates. Local water bodies, forests, and local changes in altitude may not be adequately reflected in this map’s description of your growing environment.
What Next? Future Climate Predictions
According to a 2018 study by the United States Department of Agriculture, this century will bring about great perturbations in the climatological system of America. Based on the growing degree base, or GDB index, some plants may benefit from these changes, while many others will suffer greater mortalities. Especially due to hot droughts, all regions of the United States, particularly the Northeast and Midwest regions, are almost destined to experience an increase in minimum temperatures as we shift to a warmer climate. Heat zones, defined as zones with a maximum daily temperature of about 30 degrees C or 80 degrees F are also going to warm significantly. According to the report, more than 45% of the Midwest, Northeast, Southern plains and Southwest regions will experience the increase in cumulative drought severity index, or CDSI.
Thus, even though the updated 2023 report is careful about the role of global warming, this previous report translucently indicates the grave consequences of climate change on the agricultural regions of the USA.
