Hardiness zone finder by ZIP code

What a hardiness zone actually measures

A USDA hardiness zone is one number: the average annual extreme minimum temperature at your location, taken over the 30 years from 1991 to 2020. Not the average winter, not the coldest night ever recorded. The coldest night of each year, averaged. The map slices that figure into 10°F bands (zone 5 is -20 to -10°F, zone 6 is -10 to 0°F) and then halves each band into a and b, so zone 6a is -10 to -5°F and 6b is -5 to 0°F.

That is all it is. It says nothing about summer heat, rainfall, humidity, soil, or how long your growing season runs. A plant tagged "hardy to zone 6" is a plant whose roots and crown will normally survive a -10°F night. Whether it thrives in your July is a different question, which is why gardeners in Atlanta and Seattle, both zone 8, grow very different things.

The 2023 map replaced the 2012 version and moved roughly half of the country half a zone warmer. If you learned your zone years ago, check again. Where I live the shift was enough to bring a couple of shrubs from "risky" to "fine", and that is exactly the kind of decision this number is for.

How to use your zone when you plan a garden

Use the zone as a filter, not a shopping list. Every perennial, shrub and tree sold in the US carries a zone range on the tag. If the low end of that range is your zone or colder, the plant should survive your winter in the ground. If the low end is warmer than your zone, it is an annual for you, or a container plant that comes inside, however the nursery labels it.

Then layer the things the zone does not cover. Light is the big one: the same zone 7 yard has a north-facing bed that behaves like shade woodland and a south-facing wall that behaves like a Mediterranean hillside. Drainage matters almost as much, because most "winter kill" on lavender, rosemary and many bulbs is really roots sitting in cold wet soil, not the air temperature. And within a single lot there are microclimates: a spot against a brick wall or under the eave can run a full half-zone warmer, an exposed corner that catches the wind a half-zone colder.

A practical way to work is to pick the structure of the garden (trees, hedges, the big shrubs) strictly within your zone, since those are expensive and slow to replace, and then take small risks with perennials and the odd zone-pusher in the warmest spot you have. Losing a $12 salvia in a bad winter is a lesson. Losing a 10-year-old Japanese maple is a tragedy.

• Zone tag lower than or equal to your zone: plant it in the ground.
• Zone tag one step warmer than yours: try it against a south wall, with mulch, and accept the odds.
• Zone tag two or more steps warmer: grow it in a pot and bring it in, or treat it as an annual.

The zones at a glance

The table below gives the temperature band for each full zone and a rough idea of where it falls. The a/b halves split each band in two, with a the colder half.

Where the zone number misleads people

Heat. Zones 8 and 9 include both Seattle and Phoenix, and no plant list survives that overlap. If you garden in the South or Southwest, pair your USDA zone with the AHS Heat Zone (days above 86°F per year) before you buy anything sold as "zone 8 hardy" out of a Pacific Northwest catalogue. Hostas, astilbe and most bleeding hearts are zone-hardy across the South and still cook.

Chill hours. Many fruit trees and some ornamentals (lilacs, peonies, tulips) need a certain number of hours below 45°F in winter to flower or set fruit. That is the opposite problem: a plant can be perfectly hardy in zone 9 and still never bloom there. Check chill requirements for anything fruiting once you are in zone 8 or warmer.

Snow cover. Zone 4 with reliable snow is kinder to perennials than zone 5 with bare frozen ground and freeze-thaw cycles, because snow insulates. Gardeners in the upper Midwest routinely grow plants "a zone too tender" for this reason, and gardeners in the mid-Atlantic lose plants that should have been fine.

Urban heat. Cities run warmer than the countryside around them, and the 2023 map captures some of that at the ZIP level, but a downtown courtyard surrounded by masonry is warmer still. It is common for a city garden to behave a half-zone above what the finder returns.

Where this data comes from

The lookup uses the official 2023 USDA Plant Hardiness Zone Map ZIP code tables, produced by the PRISM Climate Group at Oregon State University for the USDA Agricultural Research Service. It covers the contiguous states, Alaska, Hawaii and Puerto Rico, about 40,500 ZIP codes. Each ZIP is assigned the zone at its population-weighted centroid, so a large rural ZIP that spans a valley floor and a ridge gets one answer for both. If your ZIP is that kind of place, the interactive USDA map lets you click on your exact street.

Frequently asked questions