What is the USDA Plant Hardiness Zone?

The USDA Plant Hardiness Zone Map divides North America into 13 numbered zones and two half-zones (a/b) based on the average annual extreme minimum temperature recorded over a 30-year period. A lower zone number means colder winters. Zone 1a is the coldest (below -60°F) and Zone 13b is the warmest (above 65°F).

What temperature do I use?

Use your location's average annual extreme minimum temperature — the typical coldest night of the year averaged over many years, not the single coldest night ever recorded. Local weather sites, the USDA interactive map, or your regional extension office can provide this figure for your address.

What is the difference between zone 6a and 6b?

Each numbered zone is split into an "a" (colder) and "b" (warmer) half, each spanning 5°F (about 2.8°C). Zone 6a covers -10°F to -5°F and zone 6b covers -5°F to 0°F. A plant labeled "hardy to zone 6" is usually safe in both halves; labels that specify 6b are borderline in 6a winters.

Is hardiness zone the only factor for plant survival?

No. Hardiness zones only capture winter cold. Equally important factors include summer heat, humidity, soil drainage, rainfall, wind exposure, and microclimates. A plant may be cold-hardy for your zone but still struggle if your summers are too hot and dry, or if drainage is poor.

My zone changed from what I remember. Why?

The USDA updated the map in 2023 using temperature data from 1991–2020, replacing the 1976–2005 baseline. Many areas shifted half a zone warmer due to rising average minimum temperatures. If you learned your zone from an older source, check the 2023 map for your current zone.

Hardiness Zone Finder

Name: Hardiness Zone Finder
Availability: InStock
Author: Nham Vu

Enter your average annual minimum temperature to find your USDA Plant Hardiness Zone and learn what plants thrive there.

Your Minimum Temperature

°F

Use your average annual extreme minimum temperature — typically the coldest night of the year averaged across many years.

Quick Examples (°F)

Enter your minimum winter temperature to find your zone.

Summary

Enter your average annual minimum temperature to find your USDA Plant Hardiness Zone and learn what plants thrive there.

How it works

Enter your average annual minimum winter temperature in the input field.
Choose Fahrenheit or Celsius — the tool converts automatically.
Your USDA Plant Hardiness Zone (1a through 13b) appears instantly.
Read the zone description to understand typical winter conditions.
Browse example plants and trees that are reliably hardy in your zone.

Use cases

Verify whether a perennial, shrub, or tree will survive your winters before buying.
Compare zones when moving to a new home or planning a new garden bed.
Understand why certain plants listed as "zone 6" die back in your garden.
Select fruit trees or roses rated for a hardiness zone that matches yours.
Teach new gardeners what the zone numbers on plant tags actually mean.
Cross-reference with frost date tools to plan a complete planting schedule.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu