The USDA developed a map that defined different growing or gardening zones dividing the US into regions based on the average low winter temperatures. USDA Hardiness zones consist of 13 individual zones that define average minimum temperatures using data from different weather stations across the country.
The USDA Hardiness Map incorporates temperature data collected over a 30-year period, from 1976 to 2005. From 1-13, each subsequent zone is characterized by 10 degree Fahrenheit increments. Each zone is divided into segments “a” and “b”, representing 5 degree increments.
Zone 1 refers to the coldest region and Zone 13 is the hottest. Generally, the definition of the Zone for a region is impacted by the presence of water bodies, mountains, desert topography and variations caused by urban centers.
As a gardener, you use the USDA Hardiness Map to know the plants that are likely to succeed within your climatic zone. Pick the ideal climate for the plants you are interested in. When purchasing seeds and seedlings from a nursery, you should check the packaging for a label on its suitability for your zone. However, the USDA classification does not tell your microclimate, which is highly determinant of the success of your crops.
Below, we discuss all the USDA classifications and the best perennial vegetables to grow in each zone.
Zone 1
This represents areas experiencing average annual minimum temperatures below -50 degrees Fahrenheit.
Zone 1a -60 to -55 °F
Zone 1b -55 to -50 °F
It refers to the northernmost area of the US, especially Alaska and its surroundings. This zone experiences extremely low temperatures and is at high risk for drought. It has a short growing season and therefore planting is best done indoors. Once your plants have established their root systems, transfer them to the ground. The best vegetables to grow in this zone are those that thrive in containers.
Perennial vegetables to grow in Zone 1
- Sheep sorrel, Rumex acetosella
- Arrowhead, Sagittaria latifolia
- Oxeye Daisy, Leucanthemum vulgare
- Wild Mint, Mentha arvensis
- Stinging Nettle, Urtica dioica
- Roseroot, Rhadiola rosea
I wrote an article on 13 perennial vegetables for cold climates.
Zone 2
Represents areas with average annual minimum temperatures of -50 degrees to -40°F
Zone 2a -50 to -45 °F
Zone 2b -45 to -40 °F
The regions in this zone experience less harsh temperatures than zone 1. However, it is best to plant indoors to avoid the harsh temperatures.
Perennials to grow in Zone 2.
- Rhubarb, Rheum rhabarbarum
- Chives, Allium schoenoprasum
- Asparagus, Asparagus officinale
Zone 3
Represents average annual minimum temperatures of -40 to -30°F.
Zone 3a -40 to -35°F.
Zone 3b -35 to -30°F.
This zone encompasses the Northeastern and upper Midwest regions of the US. It can support a wider range of plants compared to the two previous zones. It incorporates New York, Idaho, Maine, Colorado, Vermont, Wisconsin, Wyoming, Minnesota and New Hampshire. Plants grown here require a lot of care and have a very short growing season. The last frost appears in mid-May and the first frost is in mid-September.
Perennials to grow in Zone 3.
- Rhubarb, Rheum x cultorum
- French sorrel, Rumex acetosa
- Asparagus, Asparagus officinalis
- Garlic chives, Allium tuberosum
- Walking Onion, Allium proliferum
- Horseradish, Armoracia rusticana
- Jerusalem artichoke, Helianthus tuberosus
Zone 4
Average annual minimum temperatures of -30 to -20°F.
Zone 4a -30 to -25°F.
Zone 4b -25 to -20°F.
This zone experiences low temperatures and encompasses the general region below zone 3. It includes states in the mid to upper Midwest such as Alaska, Nevada, New Mexico, Colorado, Montana, New York, North Dakota, Nebraska and Arizona.
The last frost typically appears from May to June and the first frost from September to October. The growing window is relatively small but supports better-growing conditions.
Perennial vegetables for Zone 4
- Dandelions, Taraxacum officinale
- Arrowhead, Syngonium podophyllum
- English sorrel, Rumex acetosa
- Common Camas, Camassia quamash
- Chicory, Cichorium intybus
- Walking Onion, Allium proliferum
- Lovage, Levisticum officinale
- Turkish Rocket, Bunias orientalis
- Wild leeks, Allium tricoccum
- Sunchoke, Helianthus tuberosus
Zone 5
Average annual minimum temperatures of -20 to -10°F.
Zone 5a -20 to -15°F.
Zone 5b -15 to -10°F.
This zone has a much longer growing season. In covers states such as Alaska, California, Connecticut, Idaho, Kansas, Illinois, Maine, Massachusetts, Maryland, Colorado, Iowa, Oregon, Ohio, New Mexico, Montana, Nebraska, South Dakota, Pennsylvania, Washington, West Virginia, Wyoming and Utah. The last frost appears in mid-May and the first frost in mid-October.
Perennials for Zone 5.
- Sage, Salvia officinalis
- Thyme, Thymus vulgaris
- Ramps, Allium tricoccum
- Parsley, Petroselinum crispum
- Mint, Mentha spp.
- Rhubarb, Rheum x cultorum
- French sorrel, Rumex acetosa
- Asparagus, Asparagus officinalis
Zone 6
Average annual minimum temperatures of -10 to 0°F.
Zone 6a -10 to -5°F.
Zone 6b -5 to 0°F.
It is warmer than zone 5 by 10 degrees. The last frost covers most of April with the first frost appearing in October. There are distinct variations in the regions within this zone, making its growing season unpredictable.
It covers state such as Alaska, Arkansas, Indiana, Kansas, Iowa, Connecticut, California, Georgia, Kentucky, New Mexico, Missouri, Montana, Oklahoma, Rhode Island, Michigan, North Carolina, West Virginia, Washington, Texas and Utah.
Perennial vegetables for Zone 6
- Walking Onions, Allium proliferum
- Shallot, Allium cepa aggregatum
- Watercress, Nasturtium officinale
- Turkish Rocket, Bunias orientalis
- Sunchokes, Helianthus tuberosus
- Chives, Allium tuberosum
- Chinese Yam, Discorea opposita
- Kale, Brassica oleracea ramosa
- Leek, Allium ampeloprasum
- Giant Solomon’s Seal, Polygonatum biflorum
- French Sorrel, Rumex acetosa
- Chicory, Cichorium intybus
- Broccoli, Brassica oleracea botrytis
Zone 7
Average annual minimum temperatures of 0 to 10°F.
Zone 7a 0 to 5°F.
Zone 7b 5 to 10°F.
It covers majority of the continental US. It has a longer growing season with the last frost in mid-April and the first frost in mid-October. It covers the following states, Alaska, Alabama, Colorado, California, Delaware, Idaho, Georgia, Oregon, Rhode Island, Mississippi, Maryland, Missouri, Pennsylvania, Tennessee, Utah, Texas, Washington and New York.
Perennials to grow in zone 7.
Many vegetables which can survive in zone 6 can also do well in zone 7.
- Tree Collards/ Tree Kale, Brassica oleracea acephala
- Shallot
- Leek
- Broccoli
- Kale
Zone 8
Average annual minimum temperatures of 10 to 20°F.
Zone 8a 10 to 15°F.
Zone 8b 15 to 20°F.
It represents regions scattered across the continental US. The last frost is in mid-March and first frost in October. It includes the following states California, Oregon, Mississippi, Arkansas, Georgia, Alabama, Texas, New Mexico, Washington, Nevada, Arizona, Utah, Florida, Tennessee, Washington DC, North and South Carolina, and Virginia.
Perennials to grow in zone 8
- Cardoon, Cynara cardunculus
- Capsicum, Capsicum annum
- Spinach, Spinacia oleracea
- Shallot, Allium cepa aggregantum
- Broccoli, Brassica oleracea botrytis
- Collards, Brassica oleracea
- Sweet potato, Ipomea batatas
- Chicory, Cichorium intybus
Zone 9
Average annual minimum temperatures of 20 to 30°F.
Zone 9a 20 to 25°F.
Zone 9b 25 to 30°F.
It has a longer planting season covering the whole year. The plants grown in this zone are typically drought-tolerant. The summers are extremely hot, larger areas are arid and water is scarce. It covers the following states, Washington, Hawaii, South Carolina, Texas, Mississippi, Utah, Oregon, Florida, Arizona, California and Alabama.
Perennials for zone 9
- Daylilies, Hemerocallis spp.
- French sorrel, Rumex acetosa
- Chayote, Sechium edule
- Artichokes, Helianthus spp.
- Walking Onions, Allium x proliferum
- Wild leek, Allium tricoccum
- Kale, Brassica oleracea var. sabellica
- American lotus, Nelumbo lutea
- Capers, Capparis spinosa
- Watercress, Nasturtium officinale
Zone 10
Average annual minimum temperatures of 30 to 40°F.
Zone 10a 30 to 35°F.
Zone 10b 35 to 40°F.
It represents areas with warm temperatures and high humidity. It is ideal for winter gardening. This zone covers the equatorial parts of North America, such as Hawaii, Florida and California. The growing season lasts from January to December; you can start planting around February. The last frost appears in late January and the first frost in December.
Perennials to grow in Zone 10
- Cardoon, Cynara cardunculus
- Japanese Ginger, Zingiber mioga
- Nine Star Broccoli, Brassica oleracea botrytis asparagoides
- Scarlet runner beans, Phaseolus coccineus
- Watercress, Nasturtium officinale
Zone 11
Average annual minimum temperatures of 40 to 50°F.
Zone 11a 40 to 45°F.
Zone 11b 45 to 50°F.
This zone is warm all year round. It is characterized by mild winters and a long growing season. It covers Hawaii, Florida and Puerto Rico. There is no frost in this region. Plants growing in this zone require ample shade, frequent watering and mulching for soil water retention.
Perennial vegetables for zone 11
- Scarlet runner beans, Phaseolus coccineus
- Eggplants, Solanum melongena
- Rainbow Chard, Beta vulgaris
- Spinach, Spinacia oleracea
- Lima bean, Phaseolus lunatus
- Hawaiian chilli pepper, Capsicum frutescens
Zone 12
Average annual minimum temperatures of 50 to 60°F
Zone 12a 50 to 55°F.
Zone 12b 55 to 60°F.
This zone is characterized by high temperatures and is suited for growing tropical plants. It covers Hawaii and Puerto Rico.
Perennial vegetables for zone 12
- Eggplant, Solanum melongena
- Sumer Squashes, Cucurbita spp.
- Cilantro, Coriandrum sativum
- Bush Beans, Phaseolus vulgaris
- Hot Peppers, Capsicum annum
- Sissoo, Dalbergia sissoo
- Spinach, Spinacia oleracea
- Lima bean, Phaseolus lunatus
Zone 13
Average annual minimum temperatures of between 60 to 70°F.
Zone 13a 60 to 65°F.
Zone 13b 65 to 70°F.
This region is frost free, and experiences high summer temperatures and low rainfall. Irrigation is required to support the growth of perennials. The growing season lasts from January to December. It covers the remote regions in Hawaii and Puerto Rico.
Perennials to grow in Zone 13
- Bush beans, Phaseolus vulgaris
- Rosemary, Salvia rosmarinus
- Hawaiian chilli pepper, Capsicum frutescens
- Ginger, Zingiber officinale
- Plantain, Plantago
- Sissoo, Dalbergia sissoo
- Spinach, Spinacia oleracea
- Lima bean, Phaseolus lunatus
Summary
The hardiness of a plant determines how well it can withstand the temperatures in a region. Any plants grown in the US are grouped according to specific Zones that offer the optimum temperature to flourish. Therefore, when planting, you can check whether your crops will tolerate the climatic conditions in your area.
