USDA GROWING ZONES: WHAT THEY MEAN FOR YOUR GARDEN

The USDA Plant Hardiness Zone Map divides the United States (and parts of Canada and Mexico) into 13 zones based on the average annual minimum winter temperature. Each zone represents a 10-degree Fahrenheit range, split into “a” (the colder half) and “b” (the warmer half).

The map has been updated several times as weather data has improved. The most recent version, published in 2023, reflects subtle shifts in climate across the country. Many gardeners discovered their zone number had changed, sometimes by half a step warmer than in earlier maps.

NOTE: USDA zones are based on the coldest temperatures a plant can withstand, not how hot it gets in summer. Zones are a guide, not a guarantee. Extreme weather events can still push conditions outside the average range.

Finding your USDA growing zone is simple. The USDA offers an interactive map where you can enter your zip code and instantly see your zone.

• Visit the USDA Plant Hardiness Zone Map
• Type in your zip code or click on your region
• The map will highlight your zone, along with the average annual minimum temperature range

Example: A gardener in Denver, Colorado, will see Zone 5b (-15° to -10°F). Someone in Houston, Texas, will see Zone 9a (20° to 25°F).

Keep in mind that if you’re right on the border of two zones, it’s usually safer to choose plants rated for the colder zone.

Many local nurseries also highlight which plants are best suited for your zone.

Knowing your USDA zone is just the starting point. Here’s how to apply it to everyday gardening decisions:

• Plant selection: Check the hardiness range on plant tags or in catalogs. If you’re in Zone 6, a shrub listed for Zones 4–8 should do fine, but one listed for Zones 7–10 may not survive your winters.
• Annual vs. perennial: A perennial in a warm zone may act as an annual in a colder one. For instance, lantana thrives as a perennial in Zone 9 but is usually treated as an annual in Zone 6.
• Planting timing: Zones influence when you can safely plant. Colder zones start later in spring and end earlier in fall, while warm-zone gardeners may enjoy two or more growing seasons in a year.
• Seasonal routines: Zones help guide tasks like when to plant bulbs, how to overwinter tender plants, and when to expect frost. Zones can also help you know when to prune, divide, or transplant perennials as well.
• Microclimates: Your garden may have warmer or cooler spots that behave like a different zone. A south-facing wall or patio can mimic a warmer zone, while a low-lying, shady corner may act like a colder one.

Hardiness zones are helpful, but they don’t tell the whole story. Many other conditions can affect how well a plant grows in your garden:

• Heat tolerance: A plant may handle cold winters but fail in extreme summer heat. For example, lilacs tolerate frigid winters but often struggle in hot, humid southern climates.
• Rainfall & humidity: USDA zones only measure winter lows, not rainfall or moisture levels. For example, Phoenix, AZ (Zone 10) and southern Florida (Zone 10) have very different growing conditions—one is hot and dry, the other hot and humid. That’s why two gardeners that have the same USDA zone assignment may have very different plant successes.
• Soil type: Clay holds water and can suffocate roots, while sandy soil drains too quickly. Amending your soil often matters more than your zone.
• Sunlight exposure: A Zone 7 perennial may thrive in full sun in the Northeast but scorch in the intense sun of the Southwest.
• Urban heat islands: Cities often stay warmer in winter due to buildings and pavement, which can nudge a garden into behaving like it’s half a zone warmer.

Think of zones as a starting framework, then adjust for your garden’s specific conditions and microclimates.

Most plant tags and catalogs in the U.S. use USDA zones, but gardeners in the West may also run into Sunset zones. The two systems look similar on the surface but measure different things.

• USDA zones are based only on average annual minimum winter temperatures. They tell you how cold your winters typically get, which helps predict if a plant will survive.
• Sunset zones consider a broader range of climate factors, including temperature, humidity, rainfall, length of growing season, elevation, and ocean influence. This makes Sunset zones especially useful in the western U.S., where conditions can vary dramatically over short distances.

Which should you use?

• USDA zones are the universal standard—you’ll find them on nearly every plant tag, nursery label, and catalog.
• Sunset zones can serve as a helpful layer of fine-tuning for western gardeners, since they reflect the region’s unique climate patterns.

Check out this video from Janey at Dig, Plant, Water, Repeat for a deeper dive on gardening zone maps.