U.S. Frost Dates by Weather Station

NOAA station USC00133438 · Iowa

Frost Dates for Greenfield, IA

NOAA weather station Greenfield (USC00133438), Iowa · elevation 1316 ft (401 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 7only 1 spring in 10 still has a frost later
  • Typical last frostApril 2550% chance of a frost after it
  • Typical first fall frostOctober 1250% chance of a frost before it
  • Frost-free season170 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Greenfield, IASpring: a frost after April 12 in 9 years out of 10, after April 25 in half of the years, after May 7 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 12 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 170 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 25First frost ~Oct 12Frost season at Greenfield, IASpring: a frost after April 12 in 9 years out of 10, after April 25 in half of the years, after May 7 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 12 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 170 days.JFMAMJJASONDLast frost ~Apr 25First frost ~Oct 12
frost likely chance fading 90% → 10% frost-free in a typical yearThe year at a glance. Blue: frost is likely; the gradient fades as the chance drops from 90% to 10%; green: the frost-free part of a typical year.

Frost dates (32°F)

Probability of frost, based on 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 7September 26
50% (typical)April 25October 12
90% (likely)April 12October 26
Frost-free season (32°F, 50% chance)
170 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 23

The last 15 years (2006–2020 normals)

Typical last frost April 26 (1 day later than the 30-year normal), typical first fall frost October 16 (4 days later). Frost-free season 172 days.

A shorter, more recent NOAA period. The 30-year normals above remain the main reference: 15 years carry more year-to-year noise.

Add these dates to your calendar Yearly reminders for the typical last frost, the lower-risk planting date and the typical first fall frost (.ics).

How the chance of frost changes with the date

Spring at Greenfield: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 7, 20% May 3, 30% May 1, 40% April 28, 50% April 25, 60% April 22, 70% April 19, 80% April 16, 90% April 12. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2024 April 21, 2025 April 16.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 7Apr 25Apr 122021: April 232022: April 272024: April 212025: April 16Fall at Greenfield: chance of a frost before this dateFall, chance of a frost before the date: 10% September 26, 20% October 1, 30% October 5, 40% October 9, 50% October 12, 60% October 15, 70% October 18, 80% October 22, 90% October 26. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2024 October 14, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 26Oct 12Oct 262021: October 222022: October 82024: October 142025: October 23
Two charts, because spring and fall answer different questions: in spring, the chance that a frost still comes after a date; in fall, the chance that the first frost has already come before it. NOAA publishes these odds from 10% to 90%, so the lines stop there. ◆ marks the actual date in each recent year.

What actually happened in recent years

Observed dates of the last spring and first fall frost (32°F) at this station; ◆ marks them on the charts above
YearLast spring frostFirst fall frost
2021April 23October 22
2022April 27October 8
2023incomplete recordincomplete record
2024April 21October 14
2025April 16October 23
2026incomplete recordseason not over yet

What these dates mean

The 170 days between the 50% dates in Greenfield bracket the period in which most garden work can be scheduled. The 32°F 50% date in spring is April 25, which carries a 50% chance of a light frost later than this date; the 32°F 50% date in fall is October 12, with a 50% chance of a light frost earlier than this date. Gardeners who prefer a cautious approach would wait until May 7, the spring date with only a 10% chance of a frost later, to set out tender crops, and would aim to finish harvesting tender crops by September 26, the fall date that has only a 10% chance of a frost earlier. The hard-frost 50% dates are April 16 and October 23, and a hard frost at 28 °F can damage plants more severely than a light frost at 32 °F.

How to read the probabilities

The dates are probabilities from 30 years of weather, not a forecast for this year.

  • Spring: "10% after May 7" means that in about one spring out of ten a frost still happens after that date. The 90% date is the earliest: a frost after it happens in most years.
  • Fall: "10% before September 26" means that in about one fall out of ten the first frost arrives before that date.
  • 50% is the typical date: half of the years are earlier, half are later.
  • A light frost (32°F) damages tender plants; a hard frost (28°F) also stops most hardy vegetables.

Nearby weather stations

Map of weather stations near Greenfield, IANumbered nearest stations: 1 — Creston, IA — 18 mi; 2 — Guthrie Center, IA — 26 mi; 3 — Atlantic, IA — 30 mi; 4 — Audubon, IA — 38 mi; 5 — Beaconsfield, IA — 40 mi.MONE25 mi · 40 km1. Creston, IA — 18 mi12. Guthrie Center, IA — 26 mi23. Atlantic, IA — 30 mi34. Audubon, IA — 38 mi45. Beaconsfield, IA — 40 mi5
  1. Creston, IA 18 mi (29 km)
  2. Guthrie Center, IA 26 mi (42 km)
  3. Atlantic, IA 30 mi (49 km)
  4. Audubon, IA 38 mi (61 km)
  5. Beaconsfield, IA 40 mi (64 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 41.2942, -94.4456.