What zone 3b means
In zone 3b, the average of the coldest night of each winter (1991 to 2020) is -35 to -30°F (-37 to -34°C). Some winters will be colder than that and some milder: the zone is an average, not the coldest temperature ever recorded. When a plant tag lists a zone range that includes 3b, the plant should survive a typical winter here. If you are in the "a" half, you are in the colder part of the zone.
Frost dates in zone 3b
Median 32°F freeze dates across 217 ZIP codes with a NOAA weather station within 60 km, from the 1991 to 2020 climate normals. Frost dates vary a lot inside a zone, because zones measure winter cold, not season length, so look up your ZIP code for your own dates.
Vegetable planting calendar for zone 3b
Purdue Extension groups vegetables by how much frost they can take and times planting from the average last spring frost. Applied to this zone's typical last frost of May 16:
| Group | Plant outdoors | Crops |
|---|---|---|
| Hardy crops (tolerate a hard frost) 4 to 6 weeks before the average last spring frost | April 4 to April 18 | Asparagus, broccoli, Brussels sprouts, cabbage, collards, horseradish, kale, kohlrabi, leek, mustard, onion, peas, potato, radish, rhubarb, spinach, turnip |
| Semi-hardy crops (tolerate a light frost) 2 to 4 weeks before the average last spring frost | April 18 to May 2 | Beet, carrot, cauliflower, celery, chard, Chinese cabbage, lettuce, mustard, parsnip |
| Tender crops (damaged by frost) after the average last spring frost, once nights stay above 50°F | From May 16 | Bean, sweet corn, tomato |
| Very tender crops (warm season) at least 2 weeks after the average last spring frost, once nights stay above 60 to 65°F | From May 30 | Cucumber, eggplant, melons, okra, pepper, pumpkin, squash, sweet potato |
Spring planting for direct seeding or transplants. A late cold snap can still happen, so watch the forecast and protect tender plants. Want today's answer for your ZIP code? Use what to plant now.
Sources: NOAA NCEI U.S. Climate Normals 1991 to 2020; Purdue Extension, Indiana Vegetable Planting Calendar (HO-186-W).
Zone 3b next to its neighbors
Zone 3a, one half zone colder, averages -40 to -35°F (-40 to -37°C). Zone 4a, one half zone warmer, averages -30 to -25°F (-34 to -32°C). On the 2023 map, about half the country moved to the next warmer half zone compared with 2012, so some gardens that were in 3a are now in 3b.
Using zone 3b when you shop
Look for the hardiness range on plant tags and in catalogs. A plant listed for "zones 1 to 5" includes zone 3b. If the range stops just above you, choose a sheltered spot, mulch roots before winter or grow it in a pot. Remember that zones describe winter cold only; heat, rainfall and soil decide the rest. How to read a plant tag.
States with the most zone 3b ZIP codes
Cities in zone 3b
Frequently asked questions
What does zone 3b mean?
Zone 3b covers places where the average coldest winter night is -35 to -30°F (-37 to -34°C). On the 2023 USDA map, 230 ZIP codes are in zone 3b.
What is the difference between zone 3a and 3b?
Each 10°F zone is split into two 5°F half zones. "a" is the colder half and "b" the warmer half. Zone 3a averages -40 to -35°F (-40 to -37°C); zone 3b averages -35 to -30°F (-37 to -34°C).
Source: 2023 USDA Plant Hardiness Zone Map ZIP code listings, PRISM Climate Group, Oregon State University; USDA ARS. Not the official USDA map.