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USDA 2023 hardiness zone · NOAA 1991–2020 frost dates

Frost dates in USDA zone 6a (-10 to -5°F)

USDA zone 6a covers places whose coldest winter night averages -10 to -5°F. Across the 763 NOAA weather stations in zone 6a, the median last spring frost is May 1, but it ranges from Apr 18 to May 23 for most stations. Enter your ZIP for your local date.

  • May 1Median last spring frostmost stations Apr 18–May 23
  • Oct 14Median first fall frost50% chance of 32°F by this date
  • 165 daysMedian growing seasonbetween 32°F freezes
  • 5,187ZIP codes in zone 6a-10 to -5°F average coldest night
  • 763Stations with frost datesof 779 NOAA stations matched

Your ZIP code’s zone and frost dates

Your ZIP gives your zone and the closest NOAA station, which is a better guide than the zone-wide numbers.

5 digits, for example 20001.

From your seed packet, e.g. “start 6 weeks before last frost”.

Earliest and latest last-frost stations in zone 6a

Earliest median last spring frost, zone 6a
StationLast spring frostFirst fall frost
Virden, ILApr 7Oct 29
Lexington 3E, MOApr 8Oct 25
Long Branch Rsvr, MOApr 8Oct 28
Quincy Dam 21, ILApr 8Oct 30
Brunswick, MOApr 10Oct 29
Chicago Midway Airport 3SW, ILApr 10Nov 1
Chicago Northerly Island, ILApr 10Nov 5
Hannibal Wtr Wks, MOApr 10Oct 27
Keokuk Lock Dam 19, IAApr 10Oct 27
Shelbyville Dam, ILApr 10Oct 24
Latest median last spring frost, zone 6a
StationLast spring frostFirst fall frost
Brian Head, UTJun 21Sep 12
Red River, NMJun 19Sep 7
Hatch, UTJun 19Sep 13
Angel Fire 1S, NMJun 18Sep 8
Luna Ranger Station, NMJun 17Sep 21
Picabo, IDJun 16Sep 9
Maybell, COJun 16Sep 9
Eagle Nest, NMJun 16Sep 14
Scofield Dam, UTJun 15Sep 12
Jarbidge 7 N, NVJun 15Sep 11

Zone 6a by state

Zone 6a stations by state
StateStationsMedian last frostMedian first frost
Alaska3May 10Sep 30
Arizona3Jun 5Sep 28
California3May 13Oct 15
Colorado63May 5Oct 8
Connecticut4May 5Oct 8
Idaho23May 16Sep 27
Illinois60Apr 17Oct 21
Indiana70Apr 23Oct 19
Iowa5Apr 15Oct 22
Kansas51Apr 28Oct 14
Maine11Apr 29Oct 15
Maryland3May 6Oct 11
Massachusetts14May 1Oct 10
Michigan88May 3Oct 14
Missouri35Apr 16Oct 20
Montana12May 12Sep 29
Nebraska31Apr 24Oct 14
Nevada10Jun 2Sep 17
New Hampshire20May 3Oct 8
New Mexico27May 28Oct 1
New York43May 4Oct 14
Ohio60Apr 25Oct 20
Oregon13Jun 5Sep 18
Pennsylvania47May 6Oct 12
Utah51May 23Sep 27
Washington6May 7Oct 1
West Virginia13May 7Oct 10
Wisconsin10Apr 23Oct 24

Neighboring zones

  • Zone 5b (-15 to -10°F): median last frost May 4
  • Zone 6b (-5 to 0°F): median last frost Apr 24

All hardiness zones

How these numbers are made

Each ZIP code gets one zone from the USDA-ARS / PRISM 2023 ZIP tables, which use the map’s 1991–2020 average of the coldest winter night of each year. A ZIP code can span more than one zone, and USDA’s own lookup works by ZIP or address. Each NOAA station is assigned the most common zone among the closest ZIP codes listed on its station page (a tie goes to the zone of the closest of those ZIPs). Frost dates are NOAA’s 50%-probability (median) 32°F dates for each station, the same values shown on the station pages. Zone figures are the median, 10th and 90th percentile across stations; a first fall frost in January to June is counted in the following year.

Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.

Sources

Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.