What Hardiness Zone Am I In? USDA Zone Finder by ZIP Code

What Is a USDA Plant Hardiness Zone?

A USDA plant hardiness zone is a geographic band defined by its average annual extreme minimum temperature — the coldest night of a typical winter. Gardeners use zones to check whether a perennial, shrub or tree survives winter outdoors in a given location.

The United States Department of Agriculture divides North America into 13 zones, from zone 1 in interior Alaska to zone 13 in Puerto Rico. Plant labels, nursery catalogs and seed packets list a hardiness range such as “zones 5–9”: the plant tolerates the winter lows of every zone inside that range. The zone finder above is one of several free plant and garden tools built on the same plant data as the PlantoScan app.

How Are Hardiness Zones Calculated?

Hardiness zones are calculated from the average of each year's single lowest winter temperature over 30 years. The 2023 USDA map averages 1991–2020 readings from 13,412 weather stations and splits the results into 10 °F zones and 5 °F half zones.

The USDA Agricultural Research Service produced the 2023 map with the PRISM Climate Group at Oregon State University. PRISM interpolates station data onto a half-mile grid that accounts for elevation, slopes and nearby water, so neighboring ZIP codes can sit in different half zones. Compared with the 2012 map, about half of the country moved into the next warmer half zone. The average extreme minimum is not the record low: a winter colder than average arrives every few years, which is why plants rated right at your zone's limit benefit from winter protection.

What Do the “a” and “b” in a Hardiness Zone Mean?

The letters split each 10 °F zone into two 5 °F half zones. Half zone “a” is the colder half and “b” the warmer half, so zone 7a reaches 0 °F to 5 °F while zone 7b bottoms out at 5 °F to 10 °F.

Most plant labels list whole zones only. A plant rated to zone 7 is expected to survive zone 7a winters, so gardeners in 7b have a 5 °F safety margin while gardeners in 7a grow it right at its limit.

What Are All the USDA Hardiness Zones and Their Temperatures?

The USDA map has 26 half zones, from zone 1a at −60 °F to −55 °F up to zone 13b at 65 °F to 70 °F. Each zone page lists the states it covers and the plants from PlantoScan's catalogue that are hardy there.

ZIP code counts cover the contiguous US. Zones 1–2 occur only in Alaska and zones 12–13 only in Hawaii and Puerto Rico.

How Do I Use My Hardiness Zone to Choose Plants?

A plant survives winter outdoors when your zone falls inside its hardiness range. Choose perennials, shrubs and trees rated to your zone or a colder one, and treat plants rated only for warmer zones as annuals, container plants or houseplants.

Hardiness is one factor among several. Summer heat, rainfall, soil drainage and exposure decide whether a cold-hardy plant thrives, and microclimates shift the picture locally: a south-facing brick wall can add a half zone of warmth, while a low-lying frost pocket subtracts one. Nearly every species in the plant care guides for over 800 species lists its hardiness range next to its light, watering and soil needs, so you can compare plants against your zone before buying.

Your zone tells you what survives winter, not when to plant. Vegetables and annual flowers follow the local frost dates instead, and a frost date calculator by ZIP code turns your average last spring frost into a planting calendar.

Do Hardiness Zones Matter for Houseplants?

Hardiness zones matter for houseplants only when they spend time outdoors. Most houseplants are tropical species hardy in zones 10–12, so they need to come inside before night temperatures drop below about 50 °F in cooler zones.

Indoors, light, humidity and watering replace winter cold as the limiting factors. PlantoScan identifies a plant from a single photo and shows its hardiness zone range alongside indoor care needs — a plant identifier app with care guides is the quickest way to find out whether an unlabelled plant can move to the patio for summer.

What Are the Hardiness Zones in Each State?

Most states span three to six half zones: Texas runs from zone 6b to 10b, while Florida reaches zone 8b to 11b. Each state page shows a ZIP code zone map, the zone of every major city and the plants hardy across the state.

• Alabama7b–9b
• Arizona5b–10a
• Arkansas7a–8b
• California5b–11a
• Colorado4a–7a
• Connecticut6a–7b
• Delaware7a–8a
• Washington, D.C.7b–8a
• Florida8b–11b
• Georgia7a–9a
• Idaho4a–7b
• Illinois5a–7a
• Indiana5b–7a
• Iowa4b–6a
• Kansas6a–7a
• Kentucky6b–7b
• Louisiana8b–10a
• Maine3b–7a
• Maryland6a–8a
• Massachusetts5b–7b
• Michigan4a–7a
• Minnesota3a–5a
• Mississippi7b–9a
• Missouri5b–8a
• Montana3b–6b
• Nebraska5a–6a
• Nevada5a–10a
• New Hampshire4a–6b
• New Jersey6b–8a
• New Mexico5a–8b
• New York4a–7b
• North Carolina6b–9a
• North Dakota3b–4b
• Ohio6a–7a
• Oklahoma6b–8a
• Oregon5b–9b
• Pennsylvania5b–8a
• Rhode Island6b–7b
• South Carolina8a–9b
• South Dakota4a–5b
• Tennessee6b–8a
• Texas6b–10b
• Utah4a–8b
• Vermont4a–6a
• Virginia6a–8b
• Washington6a–9b
• West Virginia5b–7a
• Wisconsin3b–6a
• Wyoming4a–5b

Frequently Asked Questions About Hardiness Zones

Did my hardiness zone change on the 2023 USDA map?

The 2023 USDA map uses 1991–2020 temperature data instead of 1976–2005, and about half of the country shifted into the next warmer half zone. Your zone may be 5 °F warmer than on the 2012 map.

Does my hardiness zone tell me when to plant?

A hardiness zone only describes the coldest winter temperature. Planting dates depend on your local last spring frost and first fall frost, which can differ by weeks between two towns in the same zone.

Why can't the zone finder find my ZIP code?

The official USDA ZIP code table covers the contiguous United States. Alaska, Hawaii and Puerto Rico have hardiness zones on the USDA map but are not part of the ZIP code table, and some new or PO-box-only ZIP codes are missing.

Is a hardiness zone the same as a heat zone?

A hardiness zone measures winter cold, while the American Horticultural Society heat zone counts days above 86 °F. A plant can be cold hardy in your zone and still struggle in long, hot summers.