What “zone” am I in?

Southern California has many different climate zones based upon the land’s proximity to the ocean, elevation, precipitation, temperatures etc.  The inland valley’s are typically warmer with less humidity than the coastal areas.  For example, in the summer, the city of Ojai is typically much warmer (10-15 degrees) than the city of Ventura, and in the winter Ojai is typically much cooler with more rainfall than Ventura.  Add in the ocean currents, fog, wind and “climate chaos”, and it can get complicated.

A recent climate study prepared for Ventura County projects higher summer temperatures, with less frequent but more severe storm events.  More info is here.

The most common “zones” are the Sunset Climate Zones  and the USDA Plant Hardiness Zone.

The city of Ojai, just 13 miles inland from Ventura, is nestled in between the Pacific Ocean (sea level) and the Los Padres National Forest (elevation up to 5,000 feet).  Ventura, Oxnard, Carpenteria and Santa Barbara are next to the ocean, where ocean breezes and water temperatures influence the weather.  Humidity, rainfall, temperature and climate zones all influence how quickly moisture evaporates from the soil and the plants, which influences how much water our plants need.

Climate Zone Map for Ventura County

In California, the CA Irrigation Management Information System (CIMIS)  provides climate/rainfall information based on weather stations (closest one is Santa Paula) and the Water Use Plant Index WUCOLS IV  which provides information on plant water requirements for over 3,500 taxa (taxonomic plant groups) used in California landscapes.  I believe Ojai is in Zone 4, but WUCOLS has recently misclassified Ojai in coastal Zone 3, although our climate is very different from the coastal areas.  A great way to find out how much water your plants need using CIMIS data can be found at http://www.waterwonk.us

Historic Climate ZONE Information is typically measured by USDA and others. 

For Ojai, Santa Paula and Fillmore: Sunset Zone 20 and 21,  CA WUCOLS Zone 4, USDA Hardiness Zone of 9b.

For Oxnard, Ventura, Carpenteria and Santa Barbara: Sunset Zone 23 and 24,  CA WUCOLS Zone 3, USDA Hardiness Zone of 10a.

The influence of temperature is also important to your plants—some wilt and die at below freezing temperatures (bougainvillea), and some need freezing temperatures (chill hours) in order to flower and bear fruit.


USDA Plant Hardiness Zone is the AVERAGE annual low temperature (in Fahrenheit)  the plants can tolerate
USDA Plant Hardiness Zone:  Zip Code 93023 is in Zone 9b : 25 to 30 (F)
more info:  http://www.plantmaps.com/93023 and http://www.plantmaps.com/usda_hardiness_zone_map.php

Sunset Climate Zones
Sunset Zones:  Zip code 93023 is in Sunset Climate Zones 20 & 21 with 2B to the North, 22 in Upper Ojai and Santa Paula and 23 & 24 closer to the beach. Which one are you located in?

Sunset Climate Zones for Ventura & Santa Barbara Counties

Ojai is in ZONE 20: Cool winters in Southern California’s areas of occasional ocean influence

In Zones 20 and 21, the same relative pattern prevails as in Zones 18 and 19. The even-numbered zone is the climate made up of cold-air basins and hilltops, and the odd-numbered one comprises thermal belts. The difference is that Zones 20 and 21 get weather influenced by both maritime air and interior foothill air. In these transitional areas, climate boundaries often move 20 miles in 24 hours with the movements of these air masses. Because of the greater ocean influence, this climate supports a wide variety of plants.  You can see the range of them at the Los Angeles County Arboretum in Arcadia. Typical winter lows are 37° to 43°F (3 to 6°C); extreme 20-year lows average from 25 to 22°F (–4 to –6°C).Alltime record lows range from 21 to 14°F (–6 to –10°C).

Upper Ojai is in ZONE 21: Thermal belts in Southern California’s areas of occasional ocean influence

The combination of weather influences described for Zone 20 applies to Zone 21 as well. Your garden can be in ocean air or a high fog one day and in a mass of interior air (perhaps a drying Santa Ana wind from the desert) the next day. Because temperatures rarely drop very far below 30°F (–1°C), this is fine citrusgrowing country. At the same time, Zone 21 is also the mildest zone that gets sufficient winter chilling for most forms of lilacs and certain other chill-loving plants. Extreme lows—the kind you see once every 10 or 20 years—in Zone 21 average 28 to 25°F (–2 to –4°C).All-time record lows in the zone were 27 to 17°F (–3 to –8°C).

ZONE 22: Cold-winter portions of Southern California’s coastal climate

Areas falling in Zone 22 have a coastal climate (they are influenced by the ocean approximately 85 percent of the time).When temperatures drop in winter, these cold-air basins or hilltops above the air-drained slopes have lower winter temperatures than those in neighboring Zone 23. Actually, the winters are so mild here that lows seldom fall below freezing. Extreme winter lows (the coldest temperature you can expect in 20 years) average 28 to 25°F (–2 to –4°C). Gardeners who plant under overhangs or tree canopies can grow subtropical plants that would otherwise be burned by a rare frost. Such plants include bananas, tree ferns, and the like. The lack of a pronounced chilling period during the winter limits the use of such deciduous woody plants as flowering cherry and lilac. Many herbaceous perennials from colder regions fail here because the winters are too warm for them to go dormant.

ZONE 23: Thermal belts of Southern California’s coastal climate

One of the most favored areas in North America for growing subtropical plants, Zone 23 has always been Southern California’s best zone for avocados. Frosts don’t amount to much here, because 85 percent of the time, Pacific Ocean weather dominates; interior air rules only 15 percent of the time. A notorious portion of this 15 percent consists of those days when hot, dry Santa Ana winds blow. Zone 23 lacks either the summer heat or the winter cold necessary to grow pears,most apples, and most peaches. But it enjoys considerably more heat than Zone 24—enough to put the sweetness in ‘Valencia’ oranges, for example—but not enough for ‘Washington’ naval oranges, which are grown farther inland. Temperatures are mild here, but severe winters descend at times.Average lows range from 43 to 48°F (6 to 9°C), while extreme lows average from 34 to 27°F (1 to –3°C).

ZONE 2B: Warmer-summer intermountain climate

This is a zone that offers a good balance of long, warm summers and chilly winters, making it an excellent climate zone for commercial fruit growing. Winter temperatures are milder than in neighboring Zone 2a, minimums averaging from 12 to 22°F (–11 to –6°C),with extremes in the –10 to –20°F (–23 to –29°C) range. The growing season here in Zone 2b runs from 115 days in higher elevations and more northerly areas to more than 160 days in southeastern Colorado.

For fruit trees, you need to know the number of “chill hours”  or the minimum period of cold weather after which a fruit-bearing tree will blossom. This is calculated by UC Davis extension and information is available here.  Chart below shows chill hours for 2014-15 compared with recent years.

Our chill hours are between 400-600 (Santa Paula station)
Our Ojai Valley chill hours  (measured at the Santa Paula station) are between 400-600.

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