UCCE Master Gardeners of Solano County
University of California
UCCE Master Gardeners of Solano County

Gardening in Solano County

Most gardening books, catalogs, and seed packets refer to plant hardiness zones, climate zones, or growing zones. Temperature hardiness climate zones are based on normally expected high and low temperatures and serve as guides to help you know which plants will grow where you live.

Temperature is not the only factor in figuring out whether a plant will survive in your garden. Soil types, rainfall, day length, wind, humidity, and heat also play their roles. Even within a city, a street, or a spot protected by a warm wall in your own garden, there may be microclimates that affect how plants grow. The zones are only a guide and a good starting point, but you still need to determine for yourself what will and won't work in your garden.

Of 24 climate zones defined in the Sunset Western Garden Book and the 20 zones defined by the United States Department of Agriculture (USDA), California has 20 and 16, respectively.

The USDA plant hardiness map divides North America into 11 hardiness zones. Zone 1 is the coldest; zone 11 is the warmest. When you order plants from catalogs or read general garden books, you need to know your USDA zone in order to be able to interpret references correctly. The American Horticultural Society has also issued a Plant Heat Zone map.

Gardeners in the western United States sometimes are confused when confronted with the 11 Hardiness Zones created by the USDA, because we are used to a 24-zone climate system created by Sunset Magazine. The Sunset zone maps, considered the standard gardening references in the West, are more precise than the USDA's, since they factor in not only winter minimum temperatures, but also summer highs, lengths of growing seasons, humidity, and rainfall patterns.

Solano County Zones

Solano County is a diverse county, climatologically-speaking-there are 3 different Sunset Zones that it falls into.  We have 7 major cities within our county:  Benicia, Dixon, Fairfield, Rio Vista, Suisun, Vacaville, and Vallejo. 

Sunset: ZONE 9. Thermal belts of California's Central Valley.

Growing season:  late February to December with rain in the remaining months. Summer daytime temperatures are high, sunshine is almost constant during the growing season. Heat-loving plants like oleander and crape myrtle perform well in these conditions. However, fierce cold north winds blow for several days at a time in the winter. Lows spanned over a 20-year period ranged from 28 to 18 deg. F/-2 to 8 deg. C).  Vacaville is Zone 9.

Sunset: ZONE 14. Inland Northern and Central California with Some Ocean Influence.
Growing season: early Mar. to mid-Nov., with rain coming in the remaining months. Periodic intrusions of marine air temper summer heat and winter cold (lows run from 26 degrees to 16 degrees F/-3 degrees to -9 degrees C). Mediterranean-climate plants are at home here. Dixon, Fairfield and Rio Vista are Zone 14.

Sunset: Zone 17. Marine effects in Southern Oregon, Northern and Central California.

Growing season: late February to late November with mild, wet, almost frost-less winters and cool summers marked with fog or wind. Rain occurs in the other months outside of the growing season. In a 20-year period, the lowest winter temperatures ranged from 26 to 23 deg. F/2-5 deg. C).  Benicia and Vallejo are Zone 17.

Webmaster Email: jmbaumbach@ucanr.edu