1. From the Sunset Western Garden Book
Climate Zones
From the Sunset Western Garden Book

2. 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

3. 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 zones help us as gardeners determine which plants will do well in what locales
Climate zones help to describe climate conditions in a given area
This allows us as gardeners to make educated choices as we select plant materials for particular
Requirements for plants vary greatly
Some plants require long cold winters, some mild winters
Some require dry conditions, some prefer humidity

4. 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.)
The dictionary definition of climate

5. Climate (cont.) Latitude – lines running east to west
Measured in degrees – equator is 0°
Climate (cont.)
Terms
Latitude – measured in degrees north or south of the equator
As distance from the equator increases, winters are longer and colder with short days
Summers are shorter with longer days

6. Climate (cont.) As distance from the equator increases
Long, cold winters – short days
Short summers – long days

7. The Equator
A map showing the countries located along the equator

8. Some Terms Temperate –climate between tropical and polar
No prolonged extremes in weather
Some Terms
Temperate – moderate in respect to temperature; not subject to prolonged extremes of hot or cold weather
Winter Chill – accumulated hours below 45° F over the course of the winter dormant season
Elevation – measured in feet above (or below) sea level. Higher elevations tend to have longer, colder winters.

9. Some Terms Winter Chill – temperatures below 45°F
Elevation – distance above/below sea level

10. Some Terms (cont.) Evergreen – plants hold their leaves
Deciduous – plants loses their leaves
Some Terms (cont.)
Evergreen – plants that retain their leaves through the course of the year
Deciduous – plants that loose their leaves as a response to cold dormancy or drought dormancy

11. Some Terms (cont.) Marine influence
Climate determined by adjacent bodies of water
Climate is milder
Influence reduced further from ocean
Some Terms (cont.)
Marine Influence
The influence of large bodies of water, particularly the ocean greatly influences the climate on land
In our region, the climates influenced by the Pacific Ocean tend to be milder
This influence diminishes as the distance from the coast increases

12. Marine Influence
Marine Influence
Satellite image

13. Some Terms (cont.) Continental Air Influence More extremes
Colder winters, hotter summers
Precipitation throughout the year
More winds
Some Terms (cont.)
Continental Air Influence
Tends to generate more extremes in climates than the marine influence
Winters tend to be colder, summers hotter
Precipitation is more likely throughout the year
Winds become more of an issue

14. Some terms (cont.) Mountain and Hill Influence
Elevations and orientations
Blocks marine influence from pushing on land
Blocks continental influence from reaching the coasts
Some Terms (cont.)
Mountain and Hill Influence
Elevations and orientations will influence what weather patterns occur and where as a result of the marine or continental influences
Mountains can block marine influence (storms, fog, cool moist air) from pushing inland or continental influence (storms, dry hot air, winds) from reaching the coastal areas

16. 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
Some Terms (cont.)
Microclimates
Modifications to the local climate made by local terrain, such as hills, canyons, cliffs, streams, etc. as well as by hedges, windbreaks, freeways, buildings, and other man-made structures create microclimates
These features may change airflow patterns, alter day length or light intensities, trap heat during the day and slowly release it during the night, or in other ways modify local climate
A microclimate can be as simple as the local climate on a small site
Microclimates also play a part in determining the kinds of plants that will grow in your landscape

17. 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
Climate Zones
A.KA. “hardiness zones”
Zones used to assist gardeners in making selections of plant materials suited for their areas
The zones (Sunset or UDSA) are determined by geography, topography and prevailing climates for the areas
For healthy, vigorous plant growth, it is important to select plants suited to the climate of the garden
Some plants require mild wet winters and warm dry summers
Other plants require winters cold enough to cause the plant to enter dormancy along with warm wet summers
And everything in between

18. USDA “Plant Hardiness” Zones
USDA Climate Zones Map

19. 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
The USDA Plant Hardiness Zones
The USDA zones are less specific than the Sunset Climate Zones nationally
There are 11 USDA Plant Hardiness Zones
USDA Plant Hardiness Zones are regions defined by a 10 degree Fahrenheit difference in the average annual minimum temperature
The higher the zone number, the warmer the climate for gardening in that USDA Plant Hardiness Zone. Many large urban areas carry a warmer zone designation than the surrounding countryside
Areas above an arbitrary elevation are traditionally considered unsuitable for plant cropping and do not bear appropriate zone designations

20. USDA California Zones
USDA California Climate Zones and Key

21. Sunset ‘s Garden Climate Zones
Sunset’s Garden Climate Zones National Map

22. Sunset’s California Climate Zones
More specific
Shows more zones
Hilltops, hillsides and basins
Sunset’s California Climate Zones
The Sunset climate Zones are more specific
There are more zones for greater accuracy
The sunset maps show climatic differences between hilltops and hillsides and basins

23. 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
Southern California’s Sunset Zones
There are 9 local zones including the local deserts just on the other side of the mountains
Remember, the USDA shows 11 zones for the entire country
The odd numbers designate “thermal belts”
Thermal belts tend to be warmer than cold air basins or hilltops
Cold air flows or “drains” down off of thermal belts
The “cold air basins” are designated by even numbers
Cold air is heavier and flows downhill settling into cold air basins
Hilltops tend to colder as well
The elevations are higher and they can be more exposed
Cold air can drain form hilltops past thermal belts into cold air basins

24. Thermal Belts & Cold Air Basins
Thermal Belts and Cold Air basins

25. 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
Climate Zone 2a
Cold Mountain and Intermountain Areas
Coldest zone in Southern California
In San Gabriel and San Bernardino Mountains
Cold enough for adequate winter chill for sweet cherries and most apples
Winter lows to 20° to 10° F
All time lows to –20° F to –30° F
Growing days per year – 100 to 150
J F M A M J J A S O N D

26. 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
Climate Zone 3a
Mild Areas of Mountain and Intermountain Climate
Good for many varieties of deciduous fruit trees
Higher slopes of San Gabriel Mountains
Winter lows to 25°F to 15°F
All time lows to –8° F to –18° F
Growing days per year – 150 to 170
J F M A M J J A S O N D

27. 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
Zone 11
Medium to High Desert of California and Southern Nevada
Hot summers with mild nights
Cold, near freezing winter nights with 60°F days
Daytime summer temperatures over 110°F
Nighttime winter temperatures to 0°F
Growing days per year – 220
J F M A M J J A S O N D

28. 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 Zones 18 & 19
These zones inland and classified as interior climates
They are more influenced by the continental air mass than the marine influence
The marine influence affects the climate in these zones no more than 15%

29. 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
Climate Zone 18
Above and below the Thermal Belts in Southern California’s Interior Valleys
At the tops and bottoms of slopes
Colder winters and hotter summers than the thermal belts of Zone 19
Cold enough for some deciduous fruits
Hardy subtropicals and citrus may tolerate winter lows
Winter lows - 28°F to 10°F
All time lows to - 22°F to 7°F
All time high - 115°F
Growing days per year – 240
J F M A M J J A S O N D

30. 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
Zone 19
Thermal Belts Around Southern California’s Interior Valleys
Along the sides of the hills – between the cold air basins and hilltops
Good climate for citrus, avocados and macadamias
Some more tender plants can tolerate the winter lows, inc.: Bougainvilleas, Coral Trees, Giant Burmese Honeysuckle, Lady Palm, Pittosporum
Winter lows - 27°F to 22°F
All time lows to – 23° F to 17° F
Growing days per year – 270
J F M A M J J A S O N D

31. Climate Zones 20 & 21 Climate Zones 20 & 21
Equal influence between marine and continental air masses
“Onshores” and “offshores”
Climate Zones 20 and 21
About equally influenced by the continental air mass as well as the marine influence
Can be subjected to both onshore and offshore air flows

32. 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
Climate Zone 20
Cold Winters in Southern California’s Areas of Occasional Ocean Influence
Cold air basin
Supports a wide variety of plant materials
Temperatures can vary greatly and rapidly on a daily basis because of dual influence of both the marine and continental air masses
Winter lows – 28° F to 23° F
All time lows to – 21° F to 14° F
All time high - 114°F
Growing days per year – 240
J F M A M J J A S O N D

33. 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
Climate Zone 21
Thermal Belts in Southern California’s Areas of Occasional Ocean Influence
Along the sides of slopes
Large variety of plant materials can be grown
Cool enough for some varieties requiring more winter chill but warm enough to grow more tender plants with some protection
Winter lows – 36° F to 23° F
All time lows to – 27° F 18° F
Growing days per year – 270
J F M A M J J A S O N D

34. 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
Zone 22
Cold Winter Portions of Southern California’s Coastal Climate
Cold air basins and hilltops
Influenced mostly by marine air masses
Colder than neighboring zone 23
With protection of covers, overhangs and trees, many subtropicals can be grown
Winters can be too warm for many plants to enter into adequate dormancy
Winter lows - 28° F
All time lows to – 24° F to 21 ° F
All time high 111°F
Growing days per year – 270
J F M A M J J A S O N D

35. 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
Zone 23
Thermal Belts of Southern California’s Coastal Climate
Coastal influence dominates climate and weather 85% of the time
The other 15% of the time are the hot, dry Santa Ana winds
Typically very mild temperatures with occasionally sever winters
Able to grow many more varieties of tender subtropical and some tropical plants
Zone 23 lacks summer heat and winter chill required for most deciduous fruits
Warmer than neighboring Zone 24
Winter lows – 38° F to 23° F
All time lows to – 28° F to 23° F
Growing days per year – 365
J F M A M J J A S O N D

36. 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
Zone 24
Marine Influence Along the Southern California Coast
Climate dominated my marine influence
Zone 24 is stopped by high cliffs, palisades, etc, otherwise can run several miles inland where elevation changes slowly
Cooler summers with fog, overcast and moist air
Mild winters
Fuchsias thrive as do most tropicals
Winter lows – 44° F to 24° F
All time lows to - 33° F to 20° F
Growing days per year – 365
J F M A M J J A S O N D