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What's Your Climatic Zone  
Watch for more Great information from
GranPa Chuck
on Gardening & Soils in the Northern California Area.
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Idaho, Montana, Wyoming Map

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~Major Grouping of Zones~
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Cold & Snowy ~ Rainy Northwest ~
Northern & Interior-Valley ~ Southwest Desert ~ Southern California

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Cold & Snowy

Zone 1-Includes the coldest areas of the West—all of Wyoming and portions of the states surrounding it: Montana, Idaho, Utah, and Colorado. Zone 1 is also found along the Sierra Nevada range of California and Nevada.

This zone has the shortest growing season of any in the West, between 75 and 150 days. And because frosts can occur any night of the year, gardeners in this zone employ a variety of techniques to protect plants from cold and wind. It’s especially important here to choose plants that can withstand the cold. While some marginal plants may live, they’ll be susceptible to disease and pests.

Zone 2-Zone 2 differs from Zone 1 primarily in the coldness factor—average winter lows are slightly higher. Zone 2 areas cover much of Colorado and Utah, parts of eastern Oregon and Washington, and western Idaho. The high plateaus of New Mexico and Arizona, and parts of Nevada and the high country in California are also Zone 2 areas. The growing season here is usually 150 days per year (though in some areas it is 200 days). The longer season, along with slightly milder temperatures, makes it possible to grow a few more plants. In many locations, by planting windbreaks and mulching heavily, you can grow plants that would otherwise perish from the effects of wind, cold, and winter sun.

Zone 3-This is the mildest of the three snowy-weather zones in the West. It includes the fruit- and crop-growing areas along the eastern Columbia River and portions of Idaho near Boise. This zone also extends along the eastern side of the Sierra Nevada range, encompassing the Reno area, and it includes the Coast Ranges of Oregon and Washington. The growing season here is usually 160 days (although 220 days can be usual around the Walla Walla region of eastern Washington). On the east side of the Cascade Range and the Sierra Nevada, the drying winds of winter exacerbate the cold by dehydrating plants growing in frozen soil. And along the Coast Ranges in Oregon, the heavy winter rain, occasional snow, and rugged terrain combine to limit plant grown.

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Rainy Northwest

Zone 4-Many people know this zone for the miles of tulips in the Skagit Valley. In fact, this area has more spring bulbs under cultivation than all of the Netherlands. The slightly colder winters of Zone 4—compared to those of Zones 5 and 6—help induce dormancy in the bulbs. Zone 4 extends into the greater Seattle area.

Zone 5-Includes the coastline areas of Washington and Oregon that are famous for lush vegetation. While it’s not particularly warm in the summer (it’s hard to grow tomatoes in some areas), the long growing season favors flowering plants, such as fuchsias. Native plants of all types, including salal and Oregon grape (Mahonia aquifolium), thrive in this zone.

Zone 6-Includes the Willamette Valley and the areas around Portland/Vancouver, and follows the Columbia River a few miles both upriver and downriver from Portland. It’s been said that more plant varieties are grown in the Willamette Valley than in any comparable acreage anywhere in the world. Drive Interstate 5 from Medford to Portland, and you’ll see orchards and farms that are growing fruit trees, berries, hops, vegetables, and many ornamental trees and bushes. Sitting right below the Columbia River Gorge, Portland and its surrounding areas often experience periods of freezing rain and ice storms, which can kill fragile trees and shrubs.

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Northern & Interior-Valley

Zone 7-Is found in Northern California and Oregon’s Rogue River valley. While the summers are mild and ideal for many crops and gardens, the growing season is shorter than in neighboring Zones 8 and 9. The winter is also somewhat colder, making this an excellent climate to grow plants that need some winter chill to thrive, such as peonies and flowering cherries. The region is noted for its pears, apples, peaches, and cherries. Pests that bother fruit trees are a major consideration, and mulching against the cold is often necessary.

Zone 8-The center of the Central Valley is Zone 8, noted for its cold-air basins. The crops that thrive here are those needing some winter chill (similar to Zone 7). You’ll drive by miles of orchards that require the cooler winter to set fruit. You’ll also see many heat-loving plants, though mostly those that handle the cooler winters.

Zone 9-While cool air flows downward into the valley, where it gets trapped, the surrounding low-elevation foothills are warmer. This is Zone 9. Zone 9 is safest for heat-loving plants like citrus, hibiscus, melaleuca, and pittosporum. The weather can be cold in the winter, including long periods with thick tule, or ground fog. During extremely cold periods, air blowers are needed to keep the temperature from dropping too low and killing the citrus crop.

Zone 14-Covers the small Napa and Sonoma wine-growing areas of California in its cooler and marine-influenced section, and the rich farmlands of the Sacramento–San Joaquin River delta area in its warmer inland area. (Some similarly zoned areas extend down the coast almost to Santa Maria.) Fruits that need winter chilling do well here, as do shrubs needing summer heat.

Zone 15-Like Zone 14, Zone 15 favors plants that need some winter chill to succeed and has warm, sunny summers. Yet because of its proximity to the ocean, its atmosphere is more moist, and it has cooler summers and milder winters. It is found slightly farther from the ocean and from San Francisco Bay than 14, extending up and down the coast from Mendocino to Santa Maria. Like Zones 16 and 17, it has nearly year-round growing conditions.

Zone 16-Is considered by many to be one of the finest gardening climates in California. It includes thermal belts, which means it gets more heat than areas right next to the coast (Zone 17), but warmer winters than those in Zone 15. It can grow more subtropicals than 15 with less danger of winter frost. It includes areas around the greater San Francisco Bay Area, and portions near the coast south to Santa Maria.

Zone 17-Fog Country. It’s of this zone that someone (not Mark Twain) said that the coldest winter he ever experienced was a summer in San Francisco. In its cool, moist air, fuchsias, brussels sprouts, and artichokes thrive. There’s rarely any freezing weather in the winter, and summer temperatures mainly stay in the 65–70°F range. In addition to the San Francisco and Monterey bays, this zone extends in a very narrow band up the coast to Crescent City and south to Santa Maria.

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Southwest Desert

Zone 10-Found just below the mountainous regions of Arizona and New Mexico and in southern Utah. It also covers most of eastern New Mexico and parts of southern Nevada. This high-desert zone has a definite winter season; temperatures drop below 32°F from 75 to more than 100 nights each year. With such cold winters, this zone’s gardening season runs from spring through fall; plant in spring. While similar to Zone 11, it receives just a little more rainfall (an average of 12 inches per year, with half falling in July and August) and has a little less wind.

Zone 11-Like Zone 10, Zone 11 has cold winters. On the other hand, Zone 11 also is like Zone 13 in having intense summer heat. Gardeners in this zone are among the most challenged in the West. They must contend with hot summer days, cold winter days and nights, late spring frosts, and drying winds. In the Las Vegas area, there are more than 100 days each year when the temperatures are higher than 90°F. Keeping sufficient water on garden plants is especially important—the drying winds and the bright sunlight often combine to dry out even normally hardy evergreen plants, killing or badly injuring them.

Zone 12-Zones 12 and 13 are similar, the main difference being winter cold. While the average winter low temperatures are comparable, Zone 12 has more cold days. Frosts can be expected some of the time during the four winter months. In Zone 13, frosts usually occur only one month in the winter and not at all in some locations. Zone 12’s desert area is lush, comprising a highly diverse palette of plants, many of which can be included in the home garden. The best season for cool-weather crops, such as salad greens, root vegetables, and cabbage family members, starts in September or October. A typical Zone 12 area is greater Tucson, Arizona.

Zone 13-Includes the Southwest’s low- or subtropical-desert areas. You’ll find it in diverse locations such as Death Valley, California, and Phoenix, Arizona. Summer temperatures range from 106°F to 109°F, occasionally peaking higher. Here, the gardening year begins in September and October and extends through March and April. Summer rains help established native plantings survive throughout the summer, although most plants will require year-round irrigation. Many gardeners consider the summer months the dormant season, and if they work in their gardens at all, do so shortly after dawn or in the evening twilight. This is the zone famous for grapefruit and date palms.

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Southern California

Zone 18-Located inland from the ocean, was traditionally an area of apricot, peach, apple, and walnut orchards. Now it’s mostly filled with suburban communities. Zone 18 areas are usually found on hilltops and in cold-air basins, where winter lows can range from 28°F to 10°F. While it’s too hot, cold, and dry for fuchsias, you can grow many of the hardier subtropicals here.

Zone 19-A warmer version of Zone 18, Zone 19, with winter temperatures that range from 27°F to 22°F, is located next to Zone 18. It is one of the Southern California areas famous for citrus groves. You can grow macadamia nuts and avocados here, as well as many tropical and subtropical plants. Zone 19 is also an inland-valley area, only minimally affected by the ocean.

Zones 18 and 19 are viewed as a pair, with the major difference that 18 is cooler. They are both more influenced by inland climate factors than by the ocean.

Zone 20-Zone 20, while not on the coast, is influenced by the ocean more than Zones 18 and 19 are. Its winter temperature lows range from 28°F to 23°F. Because of the marine influence, you’ll find you can grow a wider range of plants in this zone than in some neighboring ones. For example, birch, jacaranda, fig, and palm trees all thrive in this zone.

Zone 21-Also influenced by the coast, Zone 21 has the mildest winter temperatures of Zones 18 to 22. Winter temperature lows range from 36°F to 23°F, rarely dipping below 30°F. Along with Zone 19, it, too, is a prime citrus-growing area.

Like Zones 18 and 19, Zones 20 and 21 are viewed as a pair. Zone 20 is the cooler of the two. In general, they’re both likely to be influenced by the ocean part of the time and by the inland climate at other times. This means that your garden may sometimes feel the effects of the hot Santa Ana winds, and sometimes the cool breezes of the Pacific Ocean.

Zone 22-A special zone that covers Southern California’s coastal canyons. Influenced by marine air, these canyons have somewhat colder winter temperatures deep in their clefts and on their hilltops. While winter temperatures in general are mild along the coast, in Zone 22 canyons you can find average annual winter lows that range from 24°F to 21°F (although they rarely fall below 28°F). If you garden in this area and include subtropical plants, you can protect many from frost damage by planting them under building overhangs or the canopies of trees.

Zone 23-One of two coastal zones in Southern California and the one more favored for growing subtropical plants. (Zone 24 is the other coastal zone.) This is the best zone for avocados, and while it isn’t as hot as inland valley zones, it is warm enough to grow warm-weather plants like gardenias. In some winters, the temperatures can drop significantly, with lows ranging from 38°F to 23°F. Along the open hills, warm summer days favor the growing of cacti and warm-weather grasses.

Zone 24-If Zone 17 in Northern California represents the typical San Francisco climate, Zone 24 exemplifies San Diego. And while it, too, runs along the coastline, and both are marked by cool marine climate and many foggy days, the San Diego zone is warmer. As in San Francisco, fuchsias thrive here. But you’ll also find many tropicals that grow nowhere else in the western states, including rubber trees (Ficus elastica) and umbrella trees (Schefflera actinophylla), both sold as house plants in most of the West.

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