Beyond USDA Zones: Why Sunset Climate Zones Offer Better Gardening Guidance

(Editor's Note: Originally published August 15, 2011. Comments welcome; authors may not respond promptly.)

USDA zones only measure winter cold. Sunset climate zones consider summer heat, aridity, humidity, rainfall patterns, solar radiation, growing season length, ocean influence, and winter cold. Widely used in the American West—where mountains, cold ocean, and seasonal rainfall create extreme climate variation per area—Sunset zones (51 total) cover all 50 states plus Canada and Mexico.

USDA Zones 6–7: Same Winter, Different Summers

At least 40 states have USDA 6–7 areas, but summer climates vary wildly:

• Juneau, AK (Sunset A3): Temperate rainforest, cool summers, long days, spring freeze-thaw challenges.
• Boise, ID / Salt Lake City, UT / Santa Fe, NM (Sunset 3A/3B): Long, warm summers (180+ day season), cold winters ideal for deciduous fruit. Irrigation needed.
• Wichita, KS (35) / Virginia Beach, VA (31) / Pittsburgh, PA (40): Warm-hot, humid summers; adequate rainfall. Key difference: growing season length.
• Asheville, NC (36): Less hot/humid at elevation; abundant rain; watch for late frosts.
• NYC / Boston (34): Warm-hot, humid; ample rain; Gulf Stream moderates slightly.

California: Sunset Zones at Their Finest

Los Angeles County alone has 10+ Sunset zones within 3 USDA zones. Topography creates extremes: pine forests to desert, sea level to 10,000 ft. Seven zones in USDA 9–10a:

• Zone 24 (Malibu, San Diego): Ocean-dominated, rarely freezes, summer highs ~70°F coast / 80s inland. 365-day season. Greenhouse-friendly.
• Zone 23 (Beverly Hills, San Juan Capistrano): Ocean 85% of time. Warmer summers, colder nights than 24. Santa Ana winds. 350-day season. Best for avocados.
• Zone 22 (Culver City, Santa Ana): Valley floors/canyon bottoms—cold air settles, causing freezes absent in 23. 270–350 day season.
• Zone 21 (Pasadena, Thousand Oaks): Ocean ~50% time. Santa Anas. Drier. 270–350 days. Source of most grocery-store lemons.
• Zone 20 (Burbank, Glendale): Cold air basins like 22. 240–290 day season.
• Zone 19 (Riverside, Pomona): Ocean 15% time. Santa Anas. Low humidity. 270–340 days. Historic citrus country.
• Zone 18 (Van Nuys, San Bernardino): Little ocean influence, cold air basins. Coldest of the seven; annual freezes. 240–280 days. Risky for citrus; once grew walnuts, sugar beets, winter wheat.

Why It Matters: A Personal Example

I lived in Zone 18 (canyon bottom)—28°F multiple times yearly. Bird-of-paradise, citrus, bougainvillea failed. Now 12 miles away in Zone 19 (hillside)—below 34°F rarely, 30°F coldest. Citrus and subtropicals thrive. USDA says both are Zone 10; Sunset correctly predicts fuchsias and tuberous begonias fail here.

How to Use Sunset Zones

Visit the Sunset website (Sunset National Garden Book or Western Garden Book). Use Plant Finder to find your zone, then search plants by characteristics or name. Books offer zone maps, plant guides for specific situations (shade, butterflies), alphabetical plant encyclopedia with zones, and gardening reference.

If winter cold isn't your only challenge—or you want better precision—explore Sunset zones. Online info is free; books widely available new and used.