What Planting Zone Am I In? USDA Hardiness Zones by ZIP Code

What a hardiness zone measures

A plant hardiness zone describes one number: the average annual extreme minimum temperature, which is the coldest night of each winter averaged over a 30-year period. The 2023 USDA map uses 1991-2020 weather data. Zones are 10°F wide, from zone 1 (coldest) to zone 13 (warmest), and each is split into a colder “a” half and a warmer “b” half 5°F apart. The table above lists the range for every half zone.

That single number decides more than any other whether a perennial plant survives winter where you live, which is why nursery tags and catalogs list a zone range. A shrub rated for zones 5-9 should come through a typical zone 5 winter. It does not promise survival in every winter: the zone is an average, not the coldest temperature ever recorded. USDA warns that a plant grown at the cold edge of its range can thrive for years and then die in one rare cold snap lasting a day or two.

Hardiness zones matter for perennials, shrubs, trees, fruit plants and bulbs left in the ground. They matter very little for annual vegetables and flowers, which live for one season and never face a winter.

What changed on the 2023 map

USDA’s Agricultural Research Service and Oregon State University’s PRISM Climate Group released the current map in November 2023, replacing the 2012 edition. The main changes:

• Newer data. The map is built from 1991-2020 temperatures, the same 30-year period NOAA uses for its current climate normals.
• More stations. It draws on 13,412 weather stations, against 7,983 for the 2012 map.
• About half the country moved. Compared with 2012, roughly half of the country shifted to the next warmer half zone; the other half stayed where it was.
• Finer detail in Alaska. Alaska is now mapped at a much finer resolution and comes out warmer, largely because more data from mountain areas captures the mild air that sits above cold valley floors in winter.
• Zones 12 and 13. These frost-free zones, for coldest nights above 50°F and 60°F, cover only Hawaii and Puerto Rico.

USDA cautions against reading the shifts as a measure of climate change. The coldest night of the year swings widely from winter to winter, and some boundary changes reflect more stations and better mapping methods. If your zone number went up, USDA’s advice is not to replace your garden: what has thrived in your yard will most likely continue to.

Why your garden may not match your zone

The map is drawn at a half-mile scale, but no map captures every yard. USDA points to several reasons a garden can be warmer or colder than its zone:

• Cities hold heat in concrete and pavement, so a downtown can sit a zone warmer than nearby countryside.
• Elevation: hilltops and mountains are colder than surrounding lowland.
• Large bodies of water that stay unfrozen moderate winter, especially downwind.
• Frost pockets: cold air drains into low spots and collects there first.
• Sheltered spots, such as the area in front of a south-facing wall, run warmer than the rest of the yard.

Cold is not the only thing that kills plants in winter. USDA lists wind, soil type, soil moisture, humidity, snow and winter sun as factors, and notes that plants entering winter dry are more easily injured. A sudden hard freeze in early fall, or a warm spell in midwinter followed by a sharp drop, can damage plants even when the zone’s average low is never reached.

Zones and frost dates are different things

This is the most common source of confusion in planting advice. A zone measures how cold winter gets. A frost date measures when the last spring frost and first fall frost usually occur. The two are related, but loosely.

Places in the same zone can have very different springs. Chicago and Denver are both in zone 6a, yet Chicago’s typical last frost comes in mid-April and Denver’s in early May. Seattle and Austin are both in zone 9a, with last frosts in early March and late February, but Austin’s average daily temperature reaches 60°F in early March and Seattle’s not until early June, so tomatoes go in months apart. Within a single half zone such as 6b, the typical last frost across its ZIP codes spans about four weeks.

That is why this site uses each ZIP code’s own frost dates, from the nearest NOAA weather station’s 1991-2020 records, to time vegetables and annual flowers, and keeps zones for choosing what survives the winter. Each zone page shows the range of frost dates found within that zone.

About these zone tables

The zone shown for each ZIP code comes from the 2023 USDA Plant Hardiness Zone Map ZIP code data published by the PRISM Climate Group at Oregon State University. This site’s zone finder, tables and zone pages are derived from that data and are not the official USDA Plant Hardiness Zone Map. To see the official interactive map, visit the USDA Agricultural Research Service’s Plant Hardiness Zone Map website.