Hardiness Zones 101: The Ultimate FAQ for Gardeners

If you want to grow orange trees in New York City, you’ll need a greenhouse. Conversely, if you live in Florida, rhubarb and spinach probably won’t do well in the humid environment. Successful gardeners use handy tools to determine their region’s hardiness zones for robust crop yields and flowers. 

However, beginner growers may wonder how they can access the Plant Hardiness Zone Map and read it correctly to their advantage. Here’s a breakdown of the tool in an easy-to-understand question-and-answer format.

What Are Hardiness Zones?

Gardeners can add shade, improve soil quality or enhance drainage in their plots of land but cannot control the weather. Therefore, if you want your plants to survive, you must ensure they can withstand local conditions. 

The U.S. Department of Agriculture (USDA) developed the Plant Hardiness Zone Map to divide geographical areas by climate and indicate which plants have the greatest opportunity for surviving in each region. Growers do not want to waste time and resources on plants with zero chance of success. 

You can also use the map to compare other regions to your own to indicate whether slight adjustments allow you to grow certain plants with sensitivities. For instance, a fruit or vegetable needing warmer weather might mean you can keep the soil warm or cover the crop during cooler nights.

Understanding the Plant Hardiness Zones

The 2023 USDA Plant Hardiness Zone Map is the most recently updated version of the tool. Growers can type in their zip code to get an exact indication of their hardiness zone. 

The map results are based on the average annual minimum winter temperature in 13 zones in the U.S. and Canada. Each zone is about 10 degrees Fahrenheit warmer or colder than the coinciding zone — Zone 1 is the coldest, and Zone 13 is the warmest. However, varying topography — mountains, lakes, shorelines and urban areas — may cause different temperatures within one region.

FAQs for Hardiness Zones

Naturally, you might have additional questions about growing plants in particular hardiness zones. Here are some common queries gardeners have for producing healthy crop yields according to where they live.

How Do You Know if a Plant Will Thrive in Your Hardiness Zone?

Once you’ve determined your hardiness zone, you’ll want to know what plants will thrive. For instance, Wilmington, North Carolina, is in 8b while Goldsboro is in 8a. When you go to the nursery, seedlings and seed packets will have a label indicating which zones are best for growing the plant. If you have further questions, you can ask one of the experts there or look it up online. 

Can You Grow Plants From Outside of Your Hardiness Zones?

As mentioned above, you can sometimes grow plants outside your hardiness zone. Generally, if a plant’s listed zones are lower than your region, it will only grow as a perennial. If it matches yours or is higher, it’s hardy enough to grow as an annual. Likewise, the conditions may be too warm if you’re trying to grow a Zone 3 or 4 plant in Zone 12. 

It could be that you simply need to make a few adjustments for plant survival. Although you shouldn’t be surprised when a plant from a different zone doesn’t do well in your region, you may have a few tricks up your sleeve.

Do Vegetables Grow in Colder Weather?

Suppose you live in one of the cooler hardiness zones. In that case, numerous hardy vegetables can withstand heavy frost below 28 F — spinach, broccoli, onions, kale, rhubarb, rutabaga, Brussels sprouts and cabbage are just a few. 

Semi-hardy vegetables — surviving temperatures between 28 F and 32 F — include carrots, parsnips, beets, lettuce, cauliflower, parsley and celery. However, with carrots and parsnips, growers might notice the tops die off. Their root systems will tolerate the colder ground temperatures, though.

What Are Microclimates?

Those regions with varying topography are known as microclimates. They are most distinct during warm seasons, with the greatest variations in temperature and humidity. A mountainous area in Zone 8 will likely experience colder temperatures even in the summer, while the surrounding valleys are warm. Additionally, coastal regions may be slightly cooler and less humid than nearby inland areas.

What Are Native Plants?

Native plants originate from and are already adapted to specific hardiness zones, so you don’t have to worry about their survival as much. They require less irrigation and maintenance than other plants and attract local wildlife and pollinators. 

They also have deep root systems that reduce runoff and erosion, improve soil fertility, and prevent pest infestations. Ultimately, this helps protect nearby crops, flowers, shrubs, and trees and decreases the amount of synthetic chemicals you must use to manage your garden. 

Will Climate Change Affect Hardiness Zones?

Climate change has significantly changed the USDA Plant Hardiness Zone Map, especially as heat-trapping air pollution warms the atmosphere. As such, the planting zones have moved north to reflect warmer temperatures in higher latitudes and elevations. 

For instance, Zone 5 and Zone 6 have shifted to areas they wouldn’t have been before, with region-specific flora and insects expanding with them. This is because winters are now warmer than they’ve ever been. However, it also means more invasive species infiltrating zones where they don’t belong. 

For example, kudzu is an invasive vine rapidly moving from the Southeast to the Mid-Atlantic, North and Midwest. The brown marmorated stink bug has also ventured into 15 new states experiencing warmer and wetter cold seasons. 

The USDA’s most recent update to the map is the first since 2012 and will likely not be the last. Dr. Christopher Daly from PRISM Climate Group at Oregon State University said 50% of the country warmed to a five-degree half zone — but it doesn’t mean you need to rethink your gardening approach too extensively just yet. 

Grow Wisely in Your Plant Hardiness Zones

The plant hardiness zones indicate what will thrive in your garden and what won’t. Although you can grow crops and flowers outside a given zone, it is wise to plant what is tried and true to ensure healthy flora.