Planting Zone by ZIP Code

How to use the zone finder

1. Type your 5-digit ZIP code. The finder loads the zone list for your area and shows the town name under the box so you can confirm it picked the right place.
2. Read the first line of the result. The number is your zone and the letter is the half zone.
3. Look at the temperature under it. That’s the average of the coldest night of each winter from 1991 to 2020, shown in Fahrenheit and Celsius.
4. Check the 2012 line if an older book or plant tag gives a different zone for your town.
5. Copy the link to send the result to someone, or open the frost dates from the result when you’re planning vegetables.

What a hardiness zone measures

A hardiness zone is a band of winter cold. For the 2023 map, released by the USDA Agricultural Research Service in November 2023, the mapmakers took the single lowest temperature of each winter at each place, then averaged those 30 lows from 1991 to 2020. That average, called the annual extreme minimum temperature, decides the zone.

Each zone covers 10 °F, starting at −60 °F for zone 1, and each half zone covers 5 °F. Zone 7b, for example, means the coldest night of a typical winter falls between 5 and 10 °F.

Plant tags use the same numbers. A shrub hardy to zone 5 should come through the winters of zone 5 and anything warmer. If you garden in 6a, plants rated for zones 4, 5, or 6 are safe bets, and a plant rated only for zone 7 is a gamble.

What zones leave out

A zone describes cold and nothing else. It doesn’t account for:

• Summer heat and humidity, which many cool-climate plants can’t take
• Rainfall and drought
• Frost dates, which set the season for vegetables and annual flowers
• Snow cover, which insulates roots, and winter wind, which dries out evergreens
• Soil drainage, since a plant that is hardy enough can still die from sitting in wet soil all winter

Where the zone comes from

The PRISM Group at Oregon State University built the 2023 map for USDA and publishes a table that assigns every listed ZIP code a half zone and temperature range. We show that table as published. It covers 40,502 ZIP codes in the 50 states and Puerto Rico. The 2012 zone comes from PRISM’s matching table for the old map.

About 600 ZIP codes in use today, many of them in big cities, aren’t on PRISM’s 2023 list. For those we borrow the zone of the closest listed ZIP code within 15 miles, compare it with that ZIP code’s own 2012 zone, and say so in the result. ZIP codes with no listed neighbor that close are left out.

The frost dates in the result come from the nearest NOAA weather station with frost records. This is not the official USDA Plant Hardiness Zone Map, and USDA and Oregon State University don’t endorse this site. The official interactive map is at planthardiness.ars.usda.gov.

Why your zone may differ from 2012

About half the country moved to the next warmer half zone on the 2023 map. USDA warns against reading that as a clean measure of climate change. The new map uses 13,412 weather stations instead of 7,983, covers a newer 30-year period, and uses better mapping methods. The coldest night of a winter also swings widely from one year to the next. A move from 5b to 6a means the average low crossed a 5-degree line, not that it rose by 5 degrees.

A worked example

Take ZIP code 80202 in downtown Denver. The finder shows zone 6a, so the coldest night of a typical winter falls between −10 and −5 °F (−23.3 to −20.6 °C). On the 2012 map the same ZIP code was 5b, half a zone colder.

At a garden center, that means a lilac or a juniper rated to zone 4 or 5 has room to spare, and a crape myrtle rated to zone 7 will likely die back or need a protected spot.

The frost line shows the other half of the story. The Denver Water Department station, 1.6 miles away, has a typical last spring frost around April 30 and first fall frost around October 12, which leaves 165 days in between. Omaha’s ZIP code 68102 is also zone 6a, yet the airport station there averages 186 days between frosts, three weeks more. Same zone, very different vegetable seasons.

Tips for using your zone

• Buy trees, shrubs, and perennials rated for your zone or a colder one. Labels from national growers often list a range, such as zones 4 to 8, and the summer end of that range matters in the South.
• Plants in pots need more margin. Roots above ground get much colder than roots in the soil, so many gardeners pick container plants rated a zone or two colder than their own.
• Learn your yard’s warm and cold spots. Cold air drains downhill and pools in low ground, while a south-facing wall or a paved courtyard can run a half zone warmer.
• Plant borderline perennials in spring, so they have a full season to root before their first winter.
• Plan vegetables with dates, not zones. The frost dates tool and the vegetable planting calendar use the same ZIP code and pick up where the zone leaves off.