Organizational Consulting for
the Do-It-Yourself Homeowner
be your guide
Please find below information regarding plant hardiness zones. Based on information obtained
elsewhere, there is a new Hardiness Zone classification. It may take a couple more years for
all plant information to be translated into the new zone categories or regions.
If you have access to an up-to-date map for hardiness zones, please let Zen Aesthetics know
about where or how to obtain it so that I can post it for future use.
Therefore, it may be wise to verify whether the fact sheet uses the latest zone information or
whether it uses the old information. If in doubt, ask the garden center of your choice.
In general, the Milwaukee area is now considered to be in Zone 5a or Zone 5b. Milwaukee
was in Zone 4a and distant suburbs were in Zone 4b in the old zone classifications.
Converting Fahrenheit into Celsius or the opposite:
The information below was obtained from: http://www.usna.usda.gov/Hardzone/index.html
The 200 US National Arboretum "Web Version" of the
1990 USDA Plant Hardiness Zone Map
Check the color of the section in your area of the map with the color key below.
Zones 2b through 6a represented here:
USDA Hardiness Zones and Average Annual Minimum Temperature Range
Introduction
This map supersedes U.S. Department of Agriculture Miscellaneous Publication 814, "Plant
Hardiness Zone Map," which was revised in 1965. This 1990 version shows in detail the
lowest temperatures that can be expected each year in the United States, Canada, and
Mexico. These temperatures are referred to as "average annual minimum temperatures" and
are based on the lowest temperatures recorded for each of the years 1974 to 1986 in the
United States and Canada and 1971 to 1984 in Mexico. The map shows 10 different zones,
each of which represents an area of winter hardiness for the plants of agriculture and our
natural landscape. It also introduces zone 11 to represent areas that have average annual
minimum temperatures above 40 F (4.4 C) and that are therefore essentially frost free.
How to Use the New Map
Zones 2-10 in the map have been subdivided into light- and dark-colored sections (a and b)
that represent 5 F (2.8 C) differences within the 10 F (5.6 C) zone. The light color of each
zone represents the colder section; the dark color, the warmer section. Zone 11 represents
any area where the average annual minimum temperature is above 40 F (4.4 C). The map shows
20 latitude and longitude lines. Areas above an arbitrary elevation are traditionally considered
unsuitable for plant cropping and do not bear appropriate zone designations. There are also
island zones that, because of elevation differences, are warmer or cooler than the surrounding
areas and are given a different zone designation. Note that many large urban areas carry a
warmer zone designation than the surrounding countryside. The map-contains as much detail
as possible, considering the vast amount of data on which it is based and its size.
In using the map to select a suitable environment for a landscape plant, today's gardeners
should keep in mind the following:
Stress Factors. We became aware of additional stresses to plants during the 1970's.
Acid rain, gaseous and particulate pollution, security lighting, and toxic wastes, among many
other stress factors, have significantly increased the potential for unsatisfactory performance
of landscape plants. We need to document the tolerances of plants to these factors.
New Plant Management Systems. New techniques of planting, transplanting, watering,
fertilizing, and providing pest control measures have done much to increase the vigor of
landscape plants. But used unwisely, these same measures can reduce plant hardiness.
Artificial Environments. We have pushed the use of plants into totally artificial
environments such as expressways, malls, elevated decks, and buildings where plant roots are
totally removed from the ground and its warming influence. The assortment of plants that can
adapt to such environments is proving to be very restricted. Hardiness ratings alone are
inadequate to guide landscapers in selecting the most successful plants.
Additional Helpful Information:
1. Basic Plant Requirements
2. How the Map Was Started
3. Why the New Map was Created
4. How the New Map Was Created
1. Basic Plant Requirements
All agriculturists, environmentalists, horticulturists, and home gardeners have one all-abiding
question about any plant they wish to introduce into their growing spaces. Will it flourish?
The ability to predict whether a newly collected species or cultivar can be successfully grown
in a location is fundamental to the continued productivity of America's agriculture and to the
survival of our landscapes. The plants in our urban spaces, farms, fields, and forests consist of
native vegetation and exotic plants introduced into our land from all over the world.
All plants must be placed in an environment that meets their basic requirements:
Day length. Day length is usually the most critical factor in regulating vegetative growth,
flower initiation and development, and the induction of dormancy. Plants survive only when the
day length promotes their growth and prepares them for the seasonal changes.
Radiation. Most plants respond to radiation in the 270- to 3000-nm region. Cloudy, rainy
days coupled with the shade provided by nearby plants and structures can significantly reduce
the amount of radiation available. Plants survive only where the amount is within a specified
range.
Temperature. Plants grow best within an optimum range of temperatures; and the range may
be wide for some species, narrow for others. Plants survive only where temperatures allow
them to metabolize.
Frost. Plants differ in ability to survive frost, their responses varying from immediate death to
sustained performance. The previous environmental and cultural conditions of plants can
often shift, but not permanently alter, their tolerance to freezing. Plants survive only when they
are adapted to subfreezing weather.
Heat. The thermal cutoff temperature varies widely from species to species. By tradition
we group plants into sun, partial sun, and shade types and plant them according to their light and
heat tolerances.
Rainfall. Gardeners need to know how much water a landscape plant requires in determining
its usability in low maintenance landscapes. Rainfall gardening often greatly limits which species
can be used successfully. Gardeners also need to know how much and how often to water
plants in high maintenance landscapes.
pH. The ability of plant roots to take up water and nutrients depends on the pH (measure of
acidity or alkalinity), presence of soluble and insoluble salts, and aeration of the growing
medium. The successful culture of all plant species requires that they be grown in a medium
within a definite pH range and with from 10 to 14 essential nutrients in appropriate balance.
Although plants may tolerate some extraneous elements and compounds, every plant species
and cultivar has well prescribed limits.
2. How the Map Was Started
Every plant can adapt to a range of environments. Gardeners have learned through experience
where the great variety of landscape plants can be grown. Over the years many schemes have
been proposed to help gardeners locate those environments when they introduce new
species, forms, and cultivars. The pooling of many of these schemes culminated in the
development of the widely used "Plant Hardiness Zone Map," under the supervision of Henry
T. Skinner, the second director of the U.S. National Arboretum. In cooperation with the
American Horticultural Society, he worked with horticultural scientists throughout the
United States to incorporate pertinent horticultural and meteorological information into the
map.
The elements of that map were-
Zones. The contiguous United States and southern Canada were divided into 10 zones
based on a 10 F (5.6 C) difference in average annual minimum temperature.
Winter Hardiness. Survival of landscape plants over winter was selected as the most
critical criterion in their adaptation to the environment.
Classification. The zone ratings were intended to indicate excellent adaptability of the
plants. Many plants may survive in warmer or colder zones. Usually, mere survival does not
represent satisfactory performance.
Interactions With Other Environmental Factors. Many other factors may come into
play in determining satisfactory growth. Wind, soil type, soil moisture, humidity, snow, and
winter sunshine may greatly affect the adaptability of plants.
Interactions With Cultural Factors. The way plants are placed in the landscape, how
they are planted, and their size and health can greatly influence satisfactory adaptability.
3. Why the New Map was Created
The "Plant Hardiness Zone Map" was published in 1960 and revised in 1965. Since then,
many changes, new interests, and new responsibilities have emerged in North American
landscaping:
Changes in Weather. We have been losing from our landscapes plants that apparently
survived the 1940's to the 1960's. Many of the hardiness zone classifications of plants are no
longer considered valid. In North America, the ranges of temperature and moisture for the
past decade were wider than those recorded for the 1940's through the 1960's.
Introduction of New Elite Forms. Our landscape industry has worked with plant
explorers and breeders to introduce many new forms of traditional plants that are adapted to a
wider range of environments than the older forms.
Scope. The continental United States is contiguous with Canada to the north and Mexico
to the south. We share more than a common border-we share indigenous plants and many
introduced plants that can be grown successfully. We needed to expand the scope to include
the whole of North America.
4. How the New Map Was Created
The average annual minimum temperature data were analyzed for Mexico, the United States,
and Canada. Of 14,500 stations that measured temperature during the period of interest,
almost 8,000 could be identified by latitude and longitude and by a valid average annual minimum
temperature (i.e., an average based on at least 10 years of data). Data from only the latter
stations were used in the map. The data were archived by Servicio Meteorologico Nacional
(Tucubaya, D.F., Mexico), the National Climatic Data Center (Asheville, NC), and
Environment Canada - Canadian Climate Centre (Downsville, Ontario). Temperature data
were compiled and maps prepared under contract with the Meteorological Evaluation
Services Co., Inc., 165 Broadway, Amityville, New York 11701. The map is an Albers
Equal Area Projection. Standard parallels of 29.5 , and 45.5 , were used to generate the map
of the three countries. The map was computer generated by latitude and longitude. Because
of the large area involved, it is not possible to draw one map that is accurate for all of North
America. The part representing the United States has the least distortion. The
Agricultural Research Service proposes to periodically evaluate weather data and issue
updated maps as necessary and appropriate.
Cold Hardiness Ratings for Selected Woody Plants
Zone 4
-30 to -20 F
-34.5 to -28.9 C
Acer saccharum (Sugar maple)
Hydrangea paniculata (Panicle hydrangea)
Juniperus chinensis (Chinese juniper)
Ligustrum amurense (Amur River privet)
Parthenocissus quinquefolia (Virginia creeper)
Spiraea x vanhouttei (Vanhouffe spirea)
Zone 5
-20 to -10 F
-28.9 to -23.3 C
Cornus florida (Flowering dogwood)
Deutzia gracilis (Slender deutzia)
Ligustrum vulgare (Common privet)
Paithenocissus tricuspidata (Boston ivy)
Rosa multiflora (Japanese rose)
Taxus cuspidata (Japanese yew)
Cold Hardiness Ratings for Selected Woody Plants
Representative plants are listed under the coldest zones in which they normally succeed:
| A |
||
| Abetiophyllum distichum (white forsythia) |
5b |
|
| Acer platanoides (Norway maple) |
4 |
|
| Aesculus x camea (red horsechestnut) |
4 |
|
| Araucaria araucana (monkey puzzle) |
7b |
|
| Arctostaphylos uva-ursi (bearberry) |
2b |
|
| Aristolochia durior (Dutchman's pipe) |
4b |
|
| Aucuba japonica (Japanese aucuba) |
7b |
|
| B |
||
| Bauhinia variegata (purple orchid tree) |
9b |
|
| Berberis danvinii (Darwin barberry) |
8 |
|
| Betula pendula (European white birch) |
3 |
|
| Bouvardia 'Coral' (Coral bouvardia) |
9 |
|
| Butia capitata (Pindo palm) |
8b |
|
| C |
||
| Camellia reticulate (reticulate camellia) |
9 |
|
| Camellia sasanqua (sasanqua camellia) |
7b |
|
| Carya illinoinensis 'Major' (pecan) |
5 (grows) |
6 (fruits) |
| Casuarina equisetifolia (Australian pine) |
||
| Ceanothus impressus (Santa Barbara ceanothus) |
||
| Cedrus deodara (deodar cedar) |
||
| Cercis chinensis (Chinese redbud) |
||
| Chamaecyparis lawsoniana (Lawson cypress) |
||
| Chamaecyparis pisifera (Sawara cypress) |
||
| Cinnamomum camphora (camphor tree) |
||
| Cistus laurifolius (laurel rockrose) |
||
| Cistus x purpureus (purple rockrose) |
||
| Comus alba (Tatarian dogwood) |
||
| Comus kousa (Japanese dogwood) |
||
| Cunninghamia lanceolata (cunninghamia) |
||
| Cytisus x praecox (Warminster broom) |
||
| E |
||
| Elaeagnus multiflora (cherry elaeagnus) |
||
| Elaeagnus pungens (thorny elaeagnus) |
||
| Eriobotrya japonica (loquat) |
||
| Euonymus alatus (winged euonymus) |
||
| Euphorbia pulcherrima (poinsettia) |
||
| F |
||
| x Fatshedera lizei (botanical-wonder) |
||
| Forsythia ovata (early forsythia) |
||
| Forsythia suspensa (weeping forsythia) |
||
| Fremontodendron mexicanum (flannel bush) |
||
| G |
||
| Ginkgo biloba (ginkgo, maidenhair-tree) |
||
| H |
||
| Hibiscus rosa-sinensis (Chinese hibiscus) |
||
| Hibiscus syriacus (shrub althea) |
||
| Hypericum 'Hidcote' (Hidcote St. Johnswort) |
||
| I |
||
| Iberis sempervirens (evergreen candytuft) |
||
| Ilex crenata 'Convexa' (convexleaf Japanese holly) |
||
| J |
||
| Jacaranda acutifolia (green ebony) |
||
| Juglans regia (English or Persian walnut) |
||
| Juniperus horizontalis (creeping juniper) |
||
| K |
||
| Koelreuteria paniculata (golden rain-tree) |
||
| L |
||
| Laburnum x watereri (Waterer laburnum) |
||
| Lagerstroemia indica (crapemyrtle) |
||
| M |
||
| Mahonia aquitolium (Oregon hollygrape) |
||
| Malus x amoldiana (Arnold crabapple) |
||
| Melia azedarach (chinaberry) |
||
| Metasequoia glyptostroboides (dawn redwood) |
||
| Myrtus communes (true myrtle) |
||
| N |
||
| Nandina domestics (heavenly bamboo) |
||
| Nerium oleander (oleander) |
||
| O |
||
| Olea europaea (common olive) |
||
| Osmanthus heterophyflus (holly osmanthus) |
||
| P |
||
| Picea abies (Norway spruce) |
||
| Pieris japonica (Japanese andromeda) |
||
| Pinus mugo var. mughus (Mugo pine) |
||
| Pinus radiata (Monterey pine) |
||
| Pinus strobus (eastern white pine) |
||
| Prunus yedoensis (Yoshino cherry) |
||
| R |
||
| Rhaphiolepis indica 'Rosea' (Indian hawthorn) |
||
| Rhododendron 'America' (hybrid rhododendron) |
8 |
|
| Rhododendron 'Loderi King George' (hybrid) |
5 |
|
| Rhododendron mollis hybrids (mollis azalea) |
48 |
|
| Rhododendron prinophyllum (roseum) (roseshell azalea) |
4 |
|
| Rhododendron 'Purple Splendor' (hybrid rhododendron) |
7 |
|
| Rhododendron southern Indian hybrids (Indian azalea) |
8b |
|
| Rosa rugosa (rugosa rose) |
3 |
|
| S |
||
| Schinus terebinthifolius (Brazilian pepper-tree) |
9b |
|
| Sequoia sempervirens (redwood) |
8 |
|
| Sequoiadendron giganteum (giant sequoia) |
7 |
|
| Stewartia pseudocamellia (Japanese stewartia) |
6 |
|
| Syringa vulgaris (common lilac) |
3b |
|
| U |
||
| Ulmus americana (American elm) |
2 |
|
| V |
||
| Vibumum burkwoodii (Burkwood viburnum) |
5b |
|
| Z |
||
| Zelkova serrata (Japanese zelkova) |
5b |
