How many zones are there?

The USDA plant hardiness map divides North America into 11 hardiness zones. Zone 1 is the coldest; zone 11 is the warmest, a tropical area found only in Hawaii and southernmost Florida. In between, the zones follow a fairly predictable pattern across the continent, though a closer look will reveal scattered patterns of variations. Generally, the colder zones are found at higher latitudes and higher elevations.

Zone 1
Minimum temperatures:
Below -50°F
(Below -46°C)
The coldest areas of the North American continent are found in Zone 1, which encompasses the extreme northern parts of Canada; parts of the Yukon Territory, Alberta, and Saskatchewan; the interior of Alaska; and parts of the Aleutians and Kodiak Island. Only the hardiest plants will survive in the extreme winter cold and short growing season of Zone 1, but some good choices for this area are Betula glandulosa (Dwarf birch), Empetrum nigrum (Crowberry), Populus tremuloides (Quaking aspen), Potentilla pensylvanica (Pennsylvania cinquefoil), Rhododendron lapponicum (Lapland rhododendron), andSalix reticulata (Netleaf willow)

Zone 2
Minimum temperatures:
-50 to -40°F
(-46 to -40°C)
Zone 2 stretches primarily across most of Northern Canada to Alaska's interior and the Bering Sea; some of the highest mountain areas of Wyoming and Montana also fall into this zone. Although still an area of extremely cold winter temperatures, Zone 2 is modified by the warming influence of large bodies of water. As in Zone 1, the growing season is short. Good plants in this region include Ajuga (Bugleweed), Betula papyrifera (Paper birch), Cornus canadensis (Bunchberry dogwood), Elaeagnus commutata (Silverberry), Larix laricina (American larch), Picea pungens (Colorado spruce), Potentilla fruticosa (Bush cinquefoil), Thuja occidentalis (American arborvitae), and Viburnum trilobum (American cranberry bush), as well as alpine rock plants such as Cerastium, Myosotis, Saxifraga, and Silene.

Zone 3
Minimum temperatures:
-40 to -30°F
(-40 to -34°C)
Zone 3 can be found in Alaska; southern Canada; along Hudson Bay and mainland Newfoundland; in the interior areas of Maine, Vermont, and upstate New York; across the northern Midwest; and into Montana. Some of the highest regions in Wyoming, Utah, and Colorado also fall in this zone. The lower latitudes mean winter is not as cold as in Zones 1 and 2, but frosts can still occur any night of the year and the growing season is short. Plants that will survive this zone include Berberis thunbergii (Japanese bayberry), Dianthus alpinus (Alpine dianthus), Elaeagnus angustifolia (Russian olive), Iris pumila (Dwarf bearded iris), Juniperus communis (Common juniper), and Malus baccata (Siberian crabapple).

Zone 4
Minimum temperatures:
-30 to -20°F
(-34 to -29°C)
Zone 4 generally falls at a more southerly latitude than Zones 1 through 3. Large bodies of water throughout much of this zone also help to create warmer winter temperatures and a longer growing season. Zone 4 gardens exist mostly in a belt across the northcentral United States from southern Montana to central Wisconsin and into Michigan, and down into the high Rocky Mountain regions of Colorado. It also includes southwest Maine, and most of the northern regions of Vermont, New Hampshire, and New York. Successful plants for this zone include Acer saccharum (Sugar maple), Hydrangea paniculata (Peegee hydrangea), Juniperus chinensis (Chinese juniper), Ligustrum amurense (Amur River privet), Parthenocissus quinquefolia Virginia creeper) and Spiraea x vanhouttei (Bridal-wreath spiraea).

Zone 5
Minimum temperatures:
-20 to -10°F
(-29 to -23°C)
Although gardeners in Zone 5 still experience winter cold, this zone benefits from lower lattitudes and an ocean influence. In the eastern United States, it stretches across Newfoundland and Nova Scotia and along the seacoast of Maine and New Hampshire. It continues through western Massachusetts and midstate New York, northern Pennsylvania, Ohio, Indiana and Illinois, much of Michigan, southern Iowa and Nebraska, northern Missouri and Kansas, and eastern Colorado. In the interior West, this zone forms a patchwork pattern that extends from New Mexico into British Columbia, the southern Alaskan coast, and the Aleutians. Gardeners here can grow apples and plants such as Cornus florida (Flowering dogwood), Deutzia gracillis (Slender deutzia), Ligustrum vulgare (Common privet), Parthenocissus tricuspidata (Boston ivy), Rosa multiflora (Japanese rose), and Taxus cuspidata (Japanese yew).

Zone 6
Minimum temperatures:
-10 to°F
(-23 to -18°C)
Zone 6's southern latitude bestows a long growing season and milder climate than Zone 5. It begins along the coasts of Massachusetts, Connecticut, Rhode Island, New York, and northern New Jersey, then extends southwest through the country's midsection to northern Texas. In the West, Zone 6 includes parts of Arizona, New Mexico, Utah, Nevada, Oregon, and Washington, then extends narrowly north along the coast of Alaska. Eastern gardeners contend with humidity, while in the West dry heat and a lack of rainfall are the gardening challenges. Good performers throughout Zone 6 include Acer palmatum (Japanese maple), Buxus sempervirens (Common box), Euonymus fortunei (Wintercreeper), Hedera helix (English ivy), Ilex opaca (American holly), and Ligustrum ovalifolium (California privet).

Zone 7
Minimum temperatures:
0 to 10°F
(-18 to -12°C)
Zone 7 is the middle ground of gardening in the United States. It covers a Southern belt from Delaware into northern Georgia, then continues west into southern Oklahoma and northern Texas. In the East, ocean influences allow Zone 7 to continue north along the New Jersey coast, Long Island, and Cape Cod. Westerly, it snakes through southern New Mexico; bits of Arizona, Nevada and southern Utah; up the eastern border of California, into the central mountainous regions of Oregon and Washington; and into Alaska's Inland Passage. With lower elevations and longer days, among the many plants that thrive in Zone 7 are Acer macrophyllum (Bigleaf maple), Rhododendron Kurume hybrids (Kurume azalea), Cedrus atlantica (Atlas cedar), Cotoneaster microphylla (Small-leaf cotoneaster) Ilex aquifolium (English holly) and Taxus baccata (English yew).

Zone 8
Minimum temperatures:
10 to 20°F
(-12 to -7°C)
Zone 8 skirts near the western and southern borders of the United States, from the rainforests of Washington's coast to the coast of North Carolina. Winters here are relatively warm, growing seasons are long, and rhododendrons flourish. In the East, you'll encounter hot, humid summers; in the Northwest, you'll enjoy mild summers with some of the best American gardening climate; and in the Southwest you'll have the definite winters and hot, dry summers of the desert. Plants for zone 8 include Arbutus unedo (Strawberry tree), Choisya ternata (Mexican orange), Olearia haastii (New Zealand daisy-bush), Pittosporum tobira (Japanese pittosporum), Prunus laurocerasus (Cherry-laurel), and Viburnum tinus (Laurenstinus).

Zone 9
Minimum temperatures:
20 to 30°F
(-7 to -1°C)
One of the smallest regions in the plant hardiness zone map, Zone 9 includes central Florida, the Gulf coast of Louisiana and Texas, much of California, and the southern Oregon coast. This mild-winter region is characterized by a long growing season and almost no winter freeze. Summers are either hot and dry or hot and humid. Although it might seem that just about any plant could do well in such a mild area, Zone 9 (and warmer) is not good for plants that require a winter chill. Those that flourish include Asparagus setaceus (Asparagus fern), Eucalyptus globulus (Tasmanian blue gum), Syzygium paniculatum (Australian bush cherry), Fuchsia hybrids (Fuchsia), and Schinus molle (California pepper tree).

Zone 10
Minimum temperatures:
30 to 40°F
(-1 to 4°C)
Zone 10 is virtually free of winter chill and is dominated by balmy ocean influences. It stretches along parts of the California coast and covers the tip of Florida, into the Florida Keys. Zone 10 can also be found in northern Kauai and the central part of the island of Hawaii. This is the home of subtropical and tropical plants, with a year-long growing season and heat modified by the ocean. Some of our most popular houseplants grow to incredible dimensions outdoors in this zone. You can't grow apples, but you can grow tropical fruits, as well as Bougainvillea spectabilis (Bougainvillea), Cassia fistula (Golden shower), Eucalyptus citriodora (Lemon eucalyptus), Ficus elastica (Rubber plant), Ensete vetricosum (Abyssinian banana), and Roystonea regia (Royal palm).

Zone 11
Minimum temperatures:
40°F and above
(4°C and above)
Tropical Zone 11 is found in Hawaii and the lowermost Florida Keys, where oceanic breezes and influences dominate. This is the true tropical paradise zone, with a mild year- round temperature and a growing season that extends year-round, where gardening dangers exist far more from tropical storms or the occasional volcano than from freezing weather. Zone 11 gardens are filled with exquisite plants such as Alonsoa meridionalis (Mask flower), Archontophoenix cunninghamiana (King palm), Coffea arabica (Coffee), Colocasia esculenta (Taro), Ficus benjamina (Weeping Chinese banyon), Hibiscus rosa-sinensis (Chinese hibiscus), Mangifera indica (Mango), Musa (Banana), Neoregelia spectabilis (Painted-fingernail plant), andVanda sanderiana hybrids (Vanda orchid)