For gardeners and farmers across the United States, the Plant Hardiness Zone Map published by the US Department of Agriculture is an essential guide to what crops and plants can thrive in their local climate. You may have missed it, but USDA revised its map in 2023.  Most of the nation was shifted into warmer zones.  Our farm, which was right on the line of Zones 6B and 7A, was moved into Zone 7B (higher numbers represent warmer temperatures). 

What are the USDA Hardiness Zones?

The plant hardiness zones divide North America into 13 different zones based on average annual minimum winter temperatures. This allows for determining which plants, flowers, vegetables, fruits, and trees are suitable for growing in each region. Zones range from the extreme cold of zone 1 in northern Alaska to the tropical heat of zones 12-13 in Hawaii and Puerto Rico.

2023 Zone Updates

So what’s changed on the new 2023 USDA zone map? In general, many locations have shifted to encompass warmer zones compared to the last time the map was updated in 2012, reflecting the warming climatic conditions across much of the United States over the last 30 years.

Some of the most significant zone “promotions” occurred across the northern United States. Cities like Minneapolis, Chicago, Detroit, Indianapolis, and Buffalo all jumped from zone 5 to zone 6, giving gardeners more opportunities to experiment with plants previously considered too tender for those climates.

Meanwhile, the Pacific Northwest cooled slightly, with cities like Portland and Seattle sliding from zone 8 to zone 7. But these relatively mild changes were overshadowed by stark differences in other parts of the country.

Many southern cities like Dallas, Atlanta, and Oklahoma City leapfrogged two whole zones, going from zone 7 to zone 9. Portions of the Southwest like Las Vegas jumped from zone 8 to zone 10. Florida stayed hot with large swaths now falling into zones 11-12, previously limited only to sections of Hawaii.

Rising Temperatures Across the US

This newly released map provides clear scientific evidence of the warming temperatures sweeping across the United States. Overall, the new zone designations reflect an increase of about 4-5°F in average minimum winter temperatures compared to the 1976-2005 baseline informing the previous map.

The reason for these changes is no surprise to climate scientists: rising greenhouse gas emissions causing anthropogenic global climate change. While a single year or two of warm conditions may throw off the calculations, the USDA maps rely on 30-year averages known as “climate normals” to provide an accurate long-term forecast for each region.

Impacts on Planting and Agriculture

So what will these new plant hardiness zones mean for gardeners, farmers, and agricultural production across the country?

On the plus side, warmer minimum temperatures could allow for extending growing seasons and introducing new crops unable to thrive in previous colder conditions. More thermal time on the calendar potentially raises yields of warm-season crops (including flowers).

However, too much “zone promotion” comes with major risks. Many beloved specialized regional crops depend on a certain amount of winter chill period for flowering and fruiting. Cherished apple, cherry, and pear harvests could be endangered without enough accumulation of winter chilling hours in newly warm-shifted zones.

The explosion of insect pest populations, invasive species, and climate-driven extreme weather events must also be carefully managed as plant hardiness zones continue marching northward and upslope into higher elevations.

Ultimately, these new USDA zone guidelines provide a powerful wake-up call that climate change is rapidly reshuffling our lived experiences of seasons and landscapes. Both home gardeners and industrial-scale farmers will need to closely monitor the changes and make thoughtful decisions about planting choices and farming practices to adapt to this new reality.