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Counties with the Warmest Hardiness Zones

Published May 2, 2026

USDA Plant Hardiness Zones divide the country into regions based on the average annual extreme minimum temperature. The warmest zones — 10a, 10b, 11a, and 11b — represent counties where winter lows rarely drop below 30-40°F, opening the door to plants that would perish anywhere else in the country.

We identified the 25 counties with the warmest hardiness zones, spanning Hawaii, South Florida, the Rio Grande Valley, and coastal Southern California.

Counties with the Warmest Hardiness Zones

Broward County, FL sits in zone 11a with a minimum winter temperature of 40°F — warm enough to grow tropical fruits and ornamentals year-round.

RankCountyStateZoneMin Temp (°F)
1Broward CountyFL11a40
2Miami-Dade CountyFL11a40
3Monroe CountyFL11b45
4Yuma CountyAZ10a30
5Alameda CountyCA10a30
6Imperial CountyCA10a30
7Los Angeles CountyCA10b35
8Marin CountyCA10a30
9Orange CountyCA10b35
10Riverside CountyCA10a30
11San Bernardino CountyCA10a30
12San Diego CountyCA10b35
13San Francisco CountyCA10b35
14San Luis Obispo CountyCA10a30
15San Mateo CountyCA10a30
16Santa Barbara CountyCA10b35
17Ventura CountyCA10a30
18Brevard CountyFL10a30
19Charlotte CountyFL10a30
20Collier CountyFL10b35
21Glades CountyFL10a30
22Hendry CountyFL10a30
23Indian River CountyFL10a30
24Lee CountyFL10b35
25Manatee CountyFL10a30

What Warm Zones Mean for Soil and Plants

In these counties, soil biology stays active nearly year-round. Microbial activity continues through winter, organic matter breaks down faster, and root systems of subtropical plants face no threat of freeze damage. The tradeoff is that cool-season vegetables and flowers may struggle without a true winter chill.

Methodology

Counties ranked by USDA Plant Hardiness Zone warmth (zone number), using the 2023 USDA PHZM. Minimum temperature represents the average annual extreme low.

Data sourced from USDA Plant Hardiness Zone Map (2023) and USDA SSURGO Soil Survey. Hardiness zone data represents average annual extreme minimum temperatures and should be used as a general guide. Local microclimates may vary significantly from county averages.

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