Know Your Zone

Southern California has the most amazing and diverse range of microclimates. To identify these and know best what you can plant and what will survive and thrive year-after-year, it's important to know your climate zone.

The U.S. Department of Agriculture provides hardiness zone maps that divides most of North America into zones based strictly on winter lows. In the So Cal region, and all the West, we have more factors that affect a plant's success. Consider the wide-ranging typography, elevation, wind flows, distance from the ocean or mountains, rain levels, fog and more. It's a long list unique to each of our areas.

Sunset Climate Zones consider the total climate: length of growing season, timing and amount of rainfall, winter lows, summer highs, wind, and humidity.

The Los Angeles Region is broken down into Sunset Climate Zones that span the cold mountains to the marine areas. For those of us in the foothills of the San Gabriel mountains you will be primarily in zones 20 or 21.

Zone 20 - Cool winters in Southern California.

"..[In Zone 20] the climate is made up of cold-air basins and hilltops, and [Zone 21] comprises thermal belts. The difference is that Zones 20 and 21 get weather influenced by both maritime air and interior 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). All time record lows range from 21 to 14°F (–6 to –10°C)."

Zone 21 - Thermal belts in Southern California

“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, this is fine citrus growing 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. Zone 21 average low 28 to 25°F”

Our local nursery’s serve a wide geographical range. Be sure you are aware of your growing zone before you purchase, not all plants, fruit trees or natives will be a good fit. Also keep in mind the mini climates around your home. For example, I will get frost in the lowest flat area of my yard, but my vegetable garden, that is on a slope near a fence that provides a buffer, doesn’t receive frost. In another part of the yard on strong Santa Ana days, the position of my home and patio creates a wind tunnel, placing a potted citrus tree in this area on my patio will have their leaves stripped off.

Also know your Chill Hours and select fruit trees carefully for your area.

Spending time getting to know your own climate to guide your plant choices will prevent frustration and lost money down the road!