About Zones
Sunset Western Climate Zones
Sunset's Western Climate Zone system divides the Western U.S. into 24 climate zones.
Each takes into account winter cold and summer heat, humidity, elevation and terrain,
latitude, and varying degrees of continental and marine influence on local climate.
Use the following descriptions to find the Sunset climate zone number that matches
conditions where you live so you can choose the right plants for your garden.
Cold and Snowy Zones: 1, 2, and 3
Rainy Northwest Zones:4, 5, and 6
Northern and Interior-alley California Zones: 7, 8, 9, 14, 15, 16, and 17
Southern Caliornia Zones: 18, 19, 20, 21, 22, 23, and 24
Southwest Desert Zones: 10, 11, 12, and 13
Find the zone number that corresponds most closely to your area by looking at our zone
finder maps.
The Cold and Snowy Zones: 1, 2, and 3
Zone 1. 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.
The Rainy Northern Zones: 4, 5, and 6
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. 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. 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.
The Northern and Interior-Valley California Zones: 7, 8, 9, 14, 15, 16, and 17
Zone 7. 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 heatloving 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. 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. 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. Zone 17 is 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.
The Southern California Zones: 18, 19, 20, 21, 22, 23, and 24
Zone 18. 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. Zone 22 is 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. Zone 23 is 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.
The Southwest Desert Zones, from California to New Mexico: 10, 11, 12, and 13
Zone 10. Zone 10 is 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. 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.
USDA Hardiness Zones
The following from: http://www.backyardgardener.com/zone
USDA and Canadian Hardiness Zones
In an attempt to answer this question, years ago botanists and horticulturists started gathering weather records
throughout North America to compile a database to show the average coldest temperatures for each region.
These records were condensed into a range of temperatures and transformed into various zones of plant
hardiness. Maps were then made to show the lines between these temperature zones.
The climactic studies and maps were undertaken by two independent groups: The Arnold Arboretum of Harvard
University in Cambridge, Massachusetts, and the United States Department of Agriculture (USDA) in Washington,
D.C. The two maps reflected some variances, but in recent years, the differences between the Arnold Arboretum
and the USDA have narrowed. Today, the USDA map, which was last updated and released in 1990 (based on
weather records from 1974-1986), is generally considered the standard measure of plant hardiness throughout
much of the United States. Hence we have the USDA Plant Hardiness Zones.
So what's wrong with plant hardiness zones?
Well, just think about this: The average minimum temperature is not the only factor in figuring out whether a
plant will survive in your garden. Soil types, rainfall, daytime temperatures, day length, wind, humidity and heat
also play their roles. For example, although both Austin, Texas and Portland, Oregon are in the same zone (8),
the local climates are dramatically different. Even within a city, a street, or a spot protected by a warm wall in
your own garden, there may be microclimates that affect how plants grow. The zones are a good starting point,
but you still need to determine for yourself what will and won't work in your garden.
Applying zone references
Plant encyclopedias may refer simply, for example, to "Zone 6," which generally means that the plant is hardy to
that zone (and will endure winters there), and generally can withstand all the warmer zones below. More detailed
information may indicate a range of zones (i.e., "Zones 4-9"), which means the plant will only grow in those
zones, and will not tolerate the colder and warmer extremes outside them. But remember, zones are only a
guide. You may find microclimates that allow you to grow more than the books say you can; by the same token,
you may find to your dismay that some precious plant -- one that's "supposed" to be hardy in your zone -- finds
its way to plant heaven instead.
Sunset Zones versus USDA Zones
Gardeners in the western United States sometimes are confused when confronted with the 11 Hardiness Zones
created by the USDA (United States Department of Agriculture), because they are used to a 24-zone climate
system created 40 years ago by Sunset Magazine. The Sunset zone maps, which cover 13 Western states, are
much more precise than the USDA's, since they factor in not only winter minimum temperatures, but also
summer highs, lengths of growing seasons, humidity, and rainfall patterns to provide a more accurate picture of
what will grow there.
If you live in the western U.S., you'll find that nurseries, garden centers, and other western gardeners usually
refer to the Sunset climate zones rather than the USDA plant hardiness zones. In fact, the Sunset zones and
maps are what are listed for each plant in Sunset's Western Garden Book and Western Garden CD-ROM, which
are considered the standard gardening references in the West.
However, the USDA zones are still of importance to western gardeners, since the USDA zones are used in the rest
of the country. When you order plants from catalogs or read general garden books, you need to know your USDA
zone in order to be able to interpret references correctly. To determine your USDA zone, use the links above.
Search Google using “USDA Zones”
The USDA Plant Hardiness Zones divide the United States and southern Canada into 11
areas based on a 10 degree Fahrenheit difference in the average annual minimum
temperature.
Zone refers to your
probable lowest
temperatures in winter
Zone 1
Zone 2
Zone 3
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8
Zone 9
Zone 10
Zone 11
-50°F
-50°
-40°
-30°
-20°
-10°
0°
10°
20°
30°
40°
to
to
to
to
to
to
to
to
to
to
-40°F
-30°F
-20°F
-10°F
0°F
10°F
20°F
30°F
40°F
50°F
Zone Key
Colorado:
Zone
Fahrenheit
Celsius
Example Cities
1
Below -50 F
Below -45.6 C
2a
-50 to -45 F
-42.8 to -45.5 C Prudhoe Bay, Alaska; Flin Flon, Manitoba (Canada)
2b
-45 to -40 F
-40.0 to -42.7 C Unalakleet, Alaska; Pinecreek, Minnesota
3a
-40 to -35 F
-37.3 to -39.9 C International Falls, Minnesota; St. Michael, Alaska
3b
-35 to -30 F
-34.5 to -37.2 C Tomahawk, Wisconsin; Sidney, Montana
4a
-30 to -25 F
-31.7 to -34.4 C Minneapolis/St.Paul, Minnesota; Lewistown, Montana
4b
-25 to -20 F
-28.9 to -31.6 C Northwood, Iowa; Nebraska
5a
-20 to -15 F
-26.2 to -28.8 C Des Moines, Iowa; Illinois
5b
-15 to -10 F
-23.4 to -26.1 C Columbia, Missouri; Mansfield, Pennsylvania
6a
-10 to -5 F
-20.6 to -23.3 C St. Louis, Missouri; Lebanon, Pennsylvania
6b
-5 to 0 F
-17.8 to -20.5 C McMinnville, Tennessee; Branson, Missouri
7a
0 to 5 F
-15.0 to -17.7 C Oklahoma City, Oklahoma; South Boston, Virginia
7b
5 to 10 F
-12.3 to -14.9 C Little Rock, Arkansas; Griffin, Georgia
8a
10 to 15 F
-9.5 to -12.2 C
Tifton, Georgia; Dallas, Texas
8b
15 to 20 F
-6.7 to -9.4 C
Austin, Texas; Gainesville, Florida
9a
20 to 25 F
-3.9 to -6.6 C
Houston, Texas; St. Augustine, Florida
9b
25 to 30 F
-1.2 to -3.8 C
Brownsville, Texas; Fort Pierce, Florida
10a
30 to 35 F
1.6 to -1.1 C
Naples, Florida; Victorville, California
10b
35 to 40 F
4.4 to 1.7 C
Miami, Florida; Coral Gables, Florida
11
above 40 F
above 4.5 C
Honolulu, Hawaii; Mazatlan, Mexico
Fairbanks, Alaska; Resolute, Northwest Territories (Canada)
The AHS Plant Heat Zone Map
by H. Marc Cathey, AHS President Emeritus
Most gardeners are familiar with the U.S. Department of Agriculture's Plant Hardiness Zone Map. By using
the map to find the zone in which you live, you will be able to determine what plants will "winter over" in
your garden and survive for many years. That map was first published in 1960 and updated in 1990. Today
nearly all American references books, nursery catalogs, and gardening magazines describe plants using
USDA Zones.
But as we all know, cold isn't the only factor determining whether our plants will survive and thrive.
Particularly during seasons of drought, we are all aware of the impact that heat has on our plants. And
although there is still disagreement in the scientific community on this issue, many believe that our planet
is becoming hotter because of changes in its atmosphere.
The effects of heat damage are more subtle than those of extreme cold, which will kill a plant instantly.
Heat damage can first appear in many different parts of the plant: Flower buds may wither, leaves may
droop or become more attractive to insects, chlorophyll may disappear so that leaves appear white or
brown, or roots may cease growing. Plant death from heat is slow and lingering. The plant may survive in a
stunted or chlorotic state for several years. When desiccation reaches a high enough level, the enzymes that
control growth are deactivated and the plant dies.
USING THE HEAT-ZONE MAP
Use the AHS Plant Heat-Zone Map in the same way that you do the Hardiness Map. Start by finding your
town or city on the map. The larger versions of the map have county outlines that may help you do this.
The 12 zones of the map indicate the average number of days each year that a given region experiences
"heat days"-temperatures over 86 degrees (30 degrees Celsius). That is the point at which plants begin
suffering physiological damage from heat. The zones range from Zone 1 (less than one heat day) to Zone
12 (more than 210 heat days).
Thousands of garden plants have now been coded for heat tolerance, with more to come in the near future.
You will see the heat zone designations joining hardiness zone designations in garden centers, references
books, and catalogs. On each plant, there will be four numbers. For example, a tulip may be 3-8, 8-1. If you
live in USDA Zone 7 and AHS Zone 7, you will know that you can leave tulips outdoors in your garden
year-round. An ageratum may be 10-11, 12-1. It can withstand summer heat throughout the United States,
but will over winter only in our warmest zones. An English wallflower may be 5-8, 6-1. It is relatively cold
hardy, but can't tolerate extreme summer heat.
Gardeners categorize plants using such tags as "annual" or "perennial," "temperate" or "tropical," but these
tags can obscure rather than illuminate our understanding of exactly how plants sense and use the growthregulating stimuli sent by their environment.
Many of the plants that we consider annuals-such as the petunia, coleus, snapdragon, and vinca-are capable
of living for years in a frost-free environment. The Heat Map will differ from the Hardiness Map in
assigning codes to "annuals," including vegetables and herbs, and ultimately field crops as well.
Plants vary in their ability to withstand heat, not only from species to species but even among individual
plants of the same species! Unusual seasons-fewer or more hot days than normal-will invariably affect
results in your garden. And even more than with the hardiness zones, we expect gardeners to find that many
plants will survive outside their designated heat zone. This is because so many other factors complicate a
plant's reaction to heat.
Most important, the AHS Plant Heat-Zone ratings assume that adequate water is supplied to the roots of the
plant at all times. The accuracy of the zone coding can be substantially distorted by a lack of water, even
for a brief period in the life of the plant.
Although some plants are naturally more drought tolerant than others, horticulture by definition means
growing plants in a protected, artificial environment where stresses are different than in nature. No plant
can survive becoming completely dessicated. Heat damage is always linked to an insufficient amount of
water being available to the plant. Herbaceous plants are 80 to 90 percent water, and woody plants are
about 50 percent water. Plant tissues must contain enough water to keep their cells turgid and to sustain the
plant's processes of chemical and energy transport.
Watering directly at the roots of a plant-through drip irrigation for instance-conserves water that would be
lost to evaporation or runoff during overhead watering. In addition, plants take in water more efficiently
when it is applied to their roots rather than their leaves. Mulching will also help conserve water.
There are other factors that can cause stress to plants and skew the heat-zone rating. Some of them are more
controllable than others.
Oxygen. Plant cells require oxygen for respiration. Either too much or too little water can cut off the
oxygen supply to the roots and lead to a toxic situation. You can control the amount of oxygen your plant
roots receive by making sure your plants have good aeration-adequate space between soil particles.
Light. Light affects plants in two ways. First, it is essential for photosynthesis-providing the energy to split
water molecules, take up and fix carbon dioxide, and synthesize the building blocks for growth and
development. Light also creates heat. Light from the entire spectrum can enter a living body, but only rays
with shorter wavelengths can exit. The energy absorbed affects the temperature of the plant. Cloud cover,
moisture in the air, and the ozone layer-factors we gardeners can't control-affect light and temperature. But
you can adjust light by choosing to situate your plant in dappled shade, for instance, if you are in its
southernmost recommended heat zone.
Daylength. Daylength is a critical factor in regulating vegetative growth, flower initiation and
development, and the induction of dormancy. The long days of summer add substantially to the potential
for heat to have a profound effect on plant survival. In herbaceous perennials and many woody species,
there is a strong interaction between temperature and daylength. This is not a controllable factor in most
home gardening situations.
Air movement. While a gentle spring breeze can "cool" a plant through transpiration as it does us, fastmoving air on a hot day can have a negative effect, rapidly dehydrating it. Air movement in a garden is
affected by natural features such as proximity to bodies of water and the presence of surrounding
vegetation, as well as structures such as buildings and roads. You can reduce air circulation by erecting
fences and planting hedges.
Surrounding structures. If the environment is wooded, transpiration from trees and shrubs will cool the
air. On the other hand, structures of brick, stone, glass, concrete, plastic, or wood will emit heat and raise
the air temperature. Gardeners wanting plants to produce early or survive in cold zones will often plant
them on the south side of a brick wall. Obviously, this would not be a good place for a plant at the southern
limit of its heat zone!
Soil pH. The ability of plant roots to take up water and nutrients depends on the relative alkalinity or
acidity of the soil. Most plants prefer a soil close to neutral (pH 7), but there are many exceptions, such as
members of the heath family, which prefer acidic soil. The successful cultivation of any plant requires that
it be grown in a medium within a specific pH range. While it is possible to manipulate the pH of soil with
amendments, it is easier to choose plants appropriate to your soil type.
Nutrients. Plants vary greatly in the ratio and form of elements they need for consistent, healthy growth.
When these are present in appropriate quantities, they are recycled over and over again as the residue of
woody material and dropped leaves accumulates and decays, creating sustainable landscapes.
HOW THE MAP WAS CREATED
The data used to create the map were obtained from the archives of the National Climatic Data Center.
From these archives, Meteorological Evaluation Services Co., Inc., in Amityville, New York-which was
also involved in the creation of the Hardiness Map-compiled and analyzed National Weather Service
(NWS) daily high temperatures recorded between 1974 and 1995. Within the contiguous 48 states, only
NWS stations that recorded maximum daily temperatures for at least 12 years were included. (Due to the
amount of missing data in Alaska and Hawaii, the 12-year requirement was reduced to seven years at
several stations.)
Because they were too difficult to map, data from weather stations at or near mountain peaks in sparsely
populated areas were not incorporated. A total of 7,831 weather stations were processed; 4,745 were used
in plotting the map.
PURCHASE A COPY OF THE MAP
Durable full-color posters of the AHS Heat-Zone Map are available for $9.95 each. To order click here or ,
call (800) 777-7931 ext. 137.
Publications - USDA Plant Hardiness Zone Map
The United States Department of Agriculture (USDA) is in the process of creating
another version of the hardiness map using new mapping technology and an
extended set of meteorological data. The new version of the revised map will include
15 plant hardiness zones to reflect growing regions for sub-tropical and tropical
plants.