Every seed packet, plant tag, and growing guide references USDA hardiness zones — but most gardeners only have a vague idea of what their zone actually means. This guide explains the entire system, zone by zone, so you can use it correctly and stop second-guessing your plant choices.
What Is a USDA Hardiness Zone?
The USDA Plant Hardiness Zone Map divides North America (and increasingly, the world) into 13 zones based on one specific measurement: the average annual extreme minimum temperature. Each zone represents a 10°F range. Zone 1 is the coldest (below -60°F) and Zone 13 is the warmest (above 60°F).
Each zone is further divided into "a" (colder half) and "b" (warmer half), creating 26 sub-zones total. So Zone 7b is warmer than Zone 7a, but cooler than Zone 8a.
Important limitation: USDA zones only describe winter cold. They say nothing about summer heat, humidity, rainfall, frost duration, or growing season length — all of which matter for food gardening. A plant may be "hardy to Zone 7" but still fail to produce in a hot, humid Zone 7 versus a mild, dry one.
Zones 1–3: Arctic and Subarctic Gardens
Average minimum: Below -40°F (-40°C)
Examples: Interior Alaska, northern Canada, Siberia
Zones 1–3 have extremely short growing seasons (60–90 frost-free days) and brutal winters. Food gardening focuses on cold-hardy annuals that can be started indoors and transplanted: lettuce, radishes, kale, peas, and cold-tolerant greens. Perennial fruits like currants, gooseberries, and certain apple varieties are the best long-term investments.
Zones 4–5: Cold Continental
Average minimum: -30°F to -10°F (-34°C to -23°C)
Examples: Minneapolis, Montreal, parts of the UK highlands, northern Germany
This is classic four-season gardening territory. The last frost typically falls in mid-April to mid-May, giving a 120–150 day growing season. Start tomatoes, peppers, and eggplant indoors in March. Cool-season crops can go out in early April. Most vegetables grow well here with proper timing. Browse our Zone 5 planting guide for city-specific data.
Zones 6–7: Moderate Temperate
Average minimum: -10°F to 10°F (-23°C to -12°C)
Examples: New York, Philadelphia, London, Paris, Tokyo, Seoul
Zones 6–7 support the widest range of food plants. Growing seasons run 160–200 days. You can grow nearly every common vegetable, herb, and fruit. Perennial herbs like rosemary and lavender survive winters with minimal protection. Check our Zone 7 plant guide.
Zones 8–9: Warm Temperate
Average minimum: 10°F to 30°F (-12°C to -1°C)
Examples: Atlanta, Dallas, Seattle, Portland, Rome, Madrid, Melbourne
Mild winters allow year-round gardening of cold-hardy crops. Summers can be intensely hot in continental climates (Dallas, Atlanta), making spring and fall the most productive seasons for vegetables. Rosemary, lavender, artichokes, and figs thrive as permanent plantings. Citrus is borderline in Zone 8, reliable in Zone 9.
See our guides for Rome, Madrid, and Melbourne.
Zones 10–11: Subtropical
Average minimum: 30°F to 50°F (-1°C to 10°C)
Examples: Miami, Honolulu, Los Angeles, Sydney, Bangkok, Singapore
Frost is rare or absent. Gardening focuses on tropical and subtropical crops year-round: tomatoes, peppers, eggplant in cooler months; tropical greens, sweet potatoes, and ginger when it's hot. Cool-season crops (lettuce, peas, spinach) must be grown in winter. Citrus, avocado, papaya, and banana grow reliably. Singapore's planting guide shows tropical year-round gardening.
Zones 12–13: Tropical
Average minimum: Above 50°F (10°C)
Examples: Equatorial regions — Mumbai in winter, parts of Central America, equatorial Africa
These zones have no frost and minimal temperature variation. Tropical crops (cassava, plantain, yam, tropical fruits) dominate. Standard temperate vegetables struggle without controlled conditions.
Zones Are a Starting Point, Not the Whole Story
GrowByCity goes beyond USDA zones by using actual climate data for each city — including average temperatures by month, rainfall, growing season length, and hemisphere-adjusted planting calendars. Find your city for a more accurate picture than any zone number can provide.
Popular city guides: New York (Zone 7) · London (Zone 9) · Toronto (Zone 6) · Sydney (Zone 10)