Climate ZonesFrom the Sunset Western Garden Book

Reading

From the Sunset Western Garden Book• Read The West’s Climate Zones: pages 16 –

41; including all inset boxes• Los Angeles & Inland map: pages 34 – 35 • Read the sections for all of the zones on

that map: Zones, 2a, 3a, 7, 11, 18 – 24; include 1a, 2b, 8 & 9 in the Antelope Valley inset

• Look at the “growing days per year” tables for the above zones

Climate

• Why are climate zones (plant hardiness zones) important?

• Climate zones help define regions

• Plants have different requirements

• Climate zones help with plant selection

Climate (cont.)

Definition• Climate – the composite or generally

prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, cloudiness and winds, throughout the year, averaged over a series of years.

(Random House Webster’s College Dictionary)

Climate (cont.)

• Latitude – lines running east to west • Measured in degrees – equator is 0°

Climate (cont.)

As distance from the equator increases• Long, cold winters – short days• Short summers – long days

The Equator

Some Terms

• Temperate –climate between tropical and polar

• No prolonged extremes in weather

Some Terms

• Winter Chill – temperatures below 45°F• Elevation – distance above/below sea

level

Some Terms (cont.)

• Evergreen – plants hold their leaves

• Deciduous – plants loses their leaves

Some Terms (cont.)

Marine influence • Climate

determined by adjacent bodies of water

• Climate is milder

• Influence reduced further from ocean

Marine Influence

Some Terms (cont.)

Continental Air Influence

• More extremes• Colder winters,

hotter summers• Precipitation

throughout the year

• More winds

Some Terms (cont.)

Microclimates• Modifications to

local climate• Changes in air,

light, heat• Localized climate

on a small site• Can determine

the plants you choose

Climate Zones

• A.K.A. “plant hardiness zones”• Determined by geography, topography

and prevailing climates• Used as a guide for plant selection• Plant requirements vary greatly

USDA “Plant Hardiness” Zones

USDA Plant Hardiness Zones

• More generalized• 11 USDA plant hardiness zones• Defined by a 10°F difference in average

annual temperatures• Higher zone numbers = warmer climate• Urban areas higher number than

surrounding countryside• High elevations often considered

unsuitable• http://planthardiness.ars.usda.gov/PHZMWeb/#

USDA California Zones

Sunset ‘s Garden Climate Zones

Sunset’s California Climate Zones• More specific• Shows more

zones • Hilltops,

hillsides and basins

Southern California’s Sunset Zones

• Divided into 11 zones

Southern California Zones• 2a, 3a, 7, 11, 18, 19, 20, 21, 22, 23 and

24• Cold Air Basins – cold air settles in• Thermal Belts – cold air “drains” away• Hilltops – cold, exposed and higher up

Thermal Belts & Cold Air Basins

Climate Zone 2a

• Cold Mountain and Intermountain Areas

• Coldest So. Cal. Zone• In the local mountains• Winter chill for cherries and apples• Winter lows 20°F to 10°F• All time lows from –20°F to –30°F• 100 to 150 GD/Y J F M A M J J A S O N D

                                                                                               

Climate Zone 3a

• Mild Areas of Mountain and Intermountain Climate

• Higher slopes• Good deciduous fruit growing areas• Winter lows 25°F to 15°F• All time lows from –8°F to –18°F• 150 to 170 GD/Y                                                                                               

J F M A M J J A S O N D

Climate Zone 11

• Medium to High Desert of California and Southern Nevada

• Cold winter nights to 0°F• Hot summers to 110°F• 220 GD/Y

                                                                                               

J F M A M J J A S O N D

Climate Zones 18 & 19

• Climate Zones 18 and 19 • Classified as “interior” climates• About 85% influenced by the

continental air mass• Only 15% marine influence

Climate Zone 18• Above and below the Thermal Belts in

Southern California’s Interior Valleys• More extreme than Zone 19• Deciduous fruits to subtropicals• Winter lows 28°F to 10°F• All time lows from –22°F to 7°F• All time highs – 115°F • 240 GD/Y

J F M A M J J A S O N D

                                                                                               

Climate Zone 19• Thermal Belts Around Southern

California’s Interior Valleys• Between hilltops and cold air basins• Subtropicals – fruits and tender

ornamentals• Winter lows 27°F to 22°F• All time lows from 23°F to 17°F• 270 GD/Y                                                                                               

J F M A M J J A S O N D

Climate Zones 20 & 21

• Climate Zones 20 & 21• Equal influence between marine and

continental air masses• “Onshores” and “offshores”

Climate Zone 20• Cold Winters in Southern California’s

Areas of Occasional Ocean Influence• Cold air basin• Large variety of plants• Large variation of temperatures• Winter lows 28°F to 23°F• All time lows from 21°F to 14°F• All time high 114°F• 240 GD/Y

J F M A M J J A S O N D

                                                                                               

Climate Zone 21

• Thermal Belts in Southern California’s Areas of Occasional Ocean Influence

• Sides of slopes• Large variety of

plants• Cool enough for

some plants

• With protection, warm enough for others

• Winter lows 36°F to 23°F

• All time lows from 27°F to 18°F

• 270 GD/Y

                                                                                               

J F M A M J J A S O N D

Climate Zone 22

• Cold Winter Portions of Southern California’s Coastal Climate

• Basins and hilltops• Marine influence• Colder than Zone 23• Many subtropicals

• Not cold enough for dormancies

• Winter lows 28°F• All time lows from

24°F to 21°F• All time high 111°F• 270 GD/Y

J F M A M J J A S O N D

                                                                                               

Climate Zone 23• Thermal Belts of

Southern California’s Coastal Climate

• 85% coastal influence

• 15% hot & dry• Santa Ana winds• Typically mild• Occasional severe

winters

• Subtropicals and tropicals

• Lacks summer heat and winter chill

• Warmer than Zone 24

• Winter lows 38°F to 23°F

• All time lows from 28°F to 23°F

• 365 GD/Y                                                                                               

J F M A M J J A S O N D

Climate Zone 24

• Marine Influence Along the Southern California Coast

• Zone 24 stopped by the cliffs

• Can run several miles inland

• Cool summers

• Mild winters• Great for tropicals• Winter lows 44°F to

24°F• All time lows from

33°F to 20°F• 365 GD/Y

                                                                                               

J F M A M J J A S O N D