Stop the press! The USDA has released a new version of its plant hardiness zone map with one major change that could affect gardeners across the country.
Have you wanted to move to a milder garden climate? Well, stay tuned, because milder winter weather may occur without a home thanks to a new hardiness zone map.
The USDA hardiness zone map has long been the standard used by gardeners, plant breeders, and researchers to determine which plants will thrive in their locations based on whether they will survive the winter.
This valuable tool for gardeners and explorers has been updated for the first time in over a decade, with many areas moved to slightly warmer regions.
According to the USDA, the newly released 2023 map is more accurate and contains more detail than previous versions. To make it more accurate than before, the new map uses data from 13,412 weather stations, compared to the 7,983 used in the 2012 map.
The map is based on a 30-year average of winter temperatures at specific locations and divides the continental United States and Canada into 10 zones, which are further subdivided into subzones. Near the Arctic, zone 1 is the coldest and zone 10 is the warmest and is located in southern Texas, California and Florida.
The new 2023 version of the map shows that almost half of the countries on the previous map drawn in 2012 have moved to the next warm subzone. a little soft
It may not seem like much, but it's a big deal. For most of my gardening life and horticultural education, North Dakota and Minnesota were originally considered Zone 3 according to the first USDA zone maps created in the 1960s and 1990s.
Since 1990, temperate zones have moved northward, and in 2012, three-quarters of North Dakota and half of Minnesota were in zone 4a. Now the 2023 map has moved to Zone 4 with all of Minnesota except a small part of North Dakota.
To further demonstrate the rise of mild winter temperatures, Zone 5 has now extended into southern Minnesota and north through South Dakota, covering nearly a third of the South, something unheard of 30 years ago.
What does this mean for gardeners? In some places, people will be able to grow new types of flowers, fruits, trees and shrubs. But before you rush out to buy a banana to plant in your garden, surviving the winter depends on more than just winter temperatures.
Although the best tool for determining winter plant survival, the USDA hardiness zone map is based solely on temperature, specifically the coldest night of the year for a given area. Of course, this low temperature is a factor that determines whether the plants will survive the winter or not.
But there are other important factors associated with the overall low temperature. For example, the hardiness zone map does not take into account the presence or absence of snow cover, which varies greatly from year to year. A zone 5 perennial can survive a winter in zone 4 with deep snow, but will die the next winter if there is no snow.
Cold injury can be more severe when humidity is low and plants are exposed to dry winter weather. Likewise, if soil moisture is too dry in the fall and plants suffer from waterlogging in the winter, plants that are considered hardy may suffer.
Microclimate also affects winter hardiness and plant hardiness is not reflected in zone maps. A microclimate is an area or part of a landscape that is more favorable for winter plant survival due to established vegetation, greater snow accumulation, or protection from wind.
A zone 4 plant that survives the winter in an inner-city microclimate may not survive when planted on a windy hill outside.
Because other hardiness factors are nearly impossible to track and measure, hardiness zones remain our best guide for choosing trees, shrubs, and perennials that will survive the winter.
USDA plant hardiness tables and other related information are available at https://planthardiness.ars.usda.gov/.
