Planting Date FinderZone, frost date, planting window

How this works

Zones, frost dates, and planting windows come from the public sources named below. The figures were gathered 2026-10-10.

Hardiness zones

Zones come from the USDA Plant Hardiness Zone Map ZIP table hosted by the PRISM Climate Group at Oregon State: https://prism.oregonstate.edu/phzm/data/2023/phzm_us_zipcode_2023.csv. Retrieved 2026-10-10, it lists 39,921 ZIP codes with a zone and a temperature band. USDA describes the map as the average annual extreme minimum winter temperature, in 10°F zones and 5°F half-zones: planthardiness.ars.usda.gov.

The table runs from 00501 through 99403. It does not include Hawaii (967–968), Alaska (995–999), or Puerto Rico (006–009). Anchorage and Honolulu are shown with frost dates and without a zone. Elsewhere, a city takes the zone of the nearest ZIP Code Tabulation Area that appears in both the PRISM file and the Census 2024 gazetteer. The page names that ZIP and the distance. When the Census point sits more than 15 miles from any zoned ZIP, the page uses a GeoNames populated-place coordinate for the same city and state. San Francisco needs that second point, because the city boundary includes the Farallon Islands. A ZIP more than 30 miles from the city point is not used. 33,002 ZIP codes have a station distance. The others have a zone only, because the gazetteer has no center point for them.

Frost dates

Frost dates come from the NOAA NCEI 1991–2020 U.S. Climate Normals, annual and seasonal product, archive dated April 4, 2023, and the station files that carry the frost dates: archive, product page, calculation methodology, station-file guide.

NOAA’s methodology says a spring date is the probability that the last spring freeze occurs on or after that date, and a fall date is the probability that the first autumn freeze occurs on or before that date. The tables here use 36°F, 32°F, and 28°F at 10%, 50%, and 90%. On a last-freeze row, 10% is the later date and 90% is the earlier date. On a first-freeze row, 10% is the earlier date and 90% is the later date. The 50% date is the median. Growing-season length is NOAA’s published figure for the number of days the season meets or exceeds at that probability.

The dates are conditional on the temperature occurring at least once in the cold season. NOAA leaves the date blank when that chance is under 10%, and when a station is too cold to compute a date. Those stations are left out.

A station is included when all six 32°F dates (last and first, at 10%, 50%, and 90%) are real calendar dates, the record is standard or representative, at least 10 years were used, and the dates follow the seasonal order NOAA defines. Standard means the normal meets World Meteorological Organization practice with 24 or more years. Representative means 10 or more years. Provisional and estimated values are left out. 6,241 U.S. stations meet that standard. Each city, and each ZIP with a center point, is matched to the nearest of those stations. The page names the station and the miles. A city page shows a zone and frost dates together when the station is within 75 miles and a zoned ZIP is within 30 miles. 998 of the 1,000 largest incorporated places meet that test. The population floor is 40,923 in the Census Bureau’s 2024 estimates of incorporated places.

Austin-Bergstrom (USW00013904) shows how to read a row: last 32°F is February 20 at 90%, March 12 at 50%, and April 2 at 10%; first 32°F is November 1 at 10%, November 16 at 50%, and December 5 at 90%; the median growing season is 252 days. The Austin city page uses the nearest qualified station, which can be closer than Bergstrom.

Planting windows

A crop page follows an extension guide, and the window is the one that guide printed. When a guide says weeks before or after the frost-free date and does not name a 10%, 50%, or 90% probability, those weeks are applied to the median (50%) last 32°F date. Weeks before the first freeze use the median first 32°F date. The crop page says which date was used.

A month named without a day, such as March or April–June, is expanded to the first day and the last day of the named months, and the page says so. “All year” is January 1 through December 31. A phrase such as “late May” or “early April,” with no day, stays a phrase. When one end of a range names a month and the other names a day, as in “April–July 15,” the month end uses the first day of that month and the printed day is kept.

When a week instruction uses “or” or a slash, as in “6 weeks before or 2 weeks after,” the two ends are one continuous span. New Jersey’s fact sheet prints month abbreviations. Consecutive months become one range. A gap, such as April and then July, stays two windows. North Carolina’s calendars mark half-month cells. Cells that share the same mark are grouped into one run, and a mark at both the start and the end of the year is one window that crosses New Year’s.

A two-week shift that a guide prints only as a sentence, without its own column of dates, stays a sentence. That includes the coastal note on the eastern North Carolina calendar and the southern and northern Ohio note. Those shifts are not turned into extra dates.

Guides cited, gathered 2026-10-10:

What the calculators do

The window check compares today’s date with the dated window from the cited guide. The fall calculator counts back the days you enter, plus any extra days you add, from the first-32°F date you choose. The seed countdown counts back the weeks you enter from the median last 32°F date, or from the first day of a cited outdoor window. The weeks come from the packet.

When the figures change

The 1991–2020 normals remain NOAA’s current 30-year set until the next release. The zone map changes when USDA publishes a new one. The extension guides are checked about once a year.

More explanation: probabilities, the 2023 map, disclaimer.