Garden Bed Math

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It froze after the last frost date: how to read the odds

Quick answer

The "average" last frost date is NOAA's 50% date: in about half of springs, a 32°F night still comes after it. So a frost a week later means you landed in the other half of springs. NOAA also publishes a 10% date, which a freeze passes in only about 1 spring in 10. For Columbus, Ohio, those are April 20 and May 7. Plan tender plants around the later date, and check the three nearest stations, since dates can differ by weeks within a few miles.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026; NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026.

Updated October 8, 2026 Sources checked October 7, 2026 Printable checklist

Pepper and tomato plants in a May vegetable bed with leaves edged in ice crystals

Why it happens

The average date is a coin flip

NOAA doesn't publish one last frost date. For each station it publishes the date at several probabilities, from 10% to 90% in steps of 10, built from 30 years of readings, 1991 to 2020. The date most charts call "average" is the 50% one.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026; NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026.

The 50% date sits in the middle, so in about half of springs the last freezing night comes after it. If you planted on that date and got frost a week later, the data was right and you landed in the later half.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

COLUMBUS WCMH, OH: NOAA 32°F dates, 1991 to 2020 Past both 1 in 10 dates 90%50%10%10%50%90% Last spring frostFirst fall frost Typical: Apr 201 in 10 later than May 7 Typical: Oct 241 in 10 earlier than Oct 13 MarAprMayJunJulAugSepOctNov Apr 20 to Oct 24: 187 days between the typical dates
NOAA's three spring and three fall dates for the station nearest zip code 43215 (Columbus, Ohio), 1991 to 2020 normals.

Read the table

Three spring dates, three fall dates

NOAA columnSpring: a freeze still comes later inColumbus springFall: the first freeze has already come inColumbus fall
10%about 1 year in 10May 7about 1 year in 10October 13
50%about half of yearsApril 20about half of yearsOctober 24
90%about 9 years in 10April 5about 9 years in 10November 4

Columbus WCMH station, nearest to zip code 43215. The spring 10% date is the latest and the fall 10% date is the earliest: those two mark the cautious edges.

Source: NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026; NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

Between the two 10% dates, May 7 and October 13, Columbus has 159 days. Between the typical dates it has 187. The first is the season you can count on in 9 years out of 10. The second is the season you get in a middle-of-the-road year.

Source: NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026.

Where it happens

The station can be the problem

A frost date belongs to one weather station, not to your zip code. Stations sit on airports, rooftops, river bottoms and hills, and a few miles can change the date by weeks. For zip code 21201 in Baltimore, the nearest station is in the city by the harbor at 20 ft, with a typical last spring frost of March 24. Cylburn, 4.4 miles away at 235 ft, says April 2. The airport station, 9.4 miles out, says April 10.

Source: NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026.

Zip code 21201 (Baltimore): the three nearest NOAA stations MD SCI CTR BALTIMORE1.2 mi, 20 ft Mar 24Nov 21242 days CYLBURN4.4 mi, 235 ft Apr 2Nov 7219 days BALTIMORE WASH INTL AP9.4 mi, 156 ft Apr 10Oct 31204 days JFMAMJJASONDTypical last spring frost 17 days apart within 9 miles
Typical frost-free season at the three NOAA stations nearest zip code 21201, 1991 to 2020 normals. Distance from the zip code center and station height on the right.

A yard in a low spot or out in open country can frost before a city station reads 32°F, so a downtown date can run early for a suburban garden. Pick the station that looks most like your yard, not just the closest one.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

Before next spring

How to set your own date, step by step

  1. Look up your zip code

    Type it into the frost date lookup. It finds the three nearest NOAA stations within 100 miles.

    Source: NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026.

  2. Pick the station like your yard

    Compare distance and height. If your garden is in a dip, near a creek or out in the open, lean toward the later spring date among the three.

  3. Write down both spring dates

    Copy the typical date and the 1 in 10 date. The gap between them is your risk window.

    Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

  4. Plan by what each plant can take

    Cool-season and hardy plants go out near the typical date. Tender transplants wait for the 1 in 10 date or a clear forecast.

    Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

  5. Log the real frosts

    Print the frost date card and write down each year's actual last and first frost. After three or four years you'll know whether your yard runs early or late against the station.

Tender transplants in a flat moved into an open garage at night with frost cloth folded on a shelf
Tender transplants are the ones worth holding back to the later date.

The other end

The same odds in fall

Fall works in mirror image. At the typical first fall frost, about half of years have already had one. The 10% fall date is the early edge: only about 1 fall in 10 freezes before it. In Columbus that's October 13, so plans for the last harvest or bringing pots in are better counted back from there than from October 24.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026; NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026.

Print it, tick it off

My frost date plan

Fill this in from the lookup, then check it each spring and fall.

  • Station chosen, its distance and height
  • Spring: typical date and 1 in 10 later date
  • Fall: 1 in 10 earlier date and typical date
  • Plants that go out at the typical date
  • Plants that wait for the 1 in 10 date
  • Forecast checked the week before planting out
  • This year's real last and first frost, written down

Open the printable frost date odds checklist

What people learn the second year

Tips and tricks

  • Read all three stations. If they disagree by more than a week, your area has big local differences. Pick the one that matches your yard's height and setting.
  • Airport stations sit in the open. An airport is flat and open. A sheltered city lot can run earlier and an open suburban yard can run later, so treat the airport as a middle guess.
  • Plant in two waves. Put out a few tender plants at the typical date and hold the rest for the 1 in 10 date. A late frost then hits only half of them. (NOAA 1991-2020 annual/seasonal normals documentation)
  • Keep the forecast in charge. The calendar sets the window. The forecast for the coming week decides the day.
  • Note where the frost hit. When frost comes late, write down which bed got it. Low corners and open lawn often frost first.

Common questions

Questions

Why did it frost after the last frost date?

Because the usual "last frost date" is NOAA's 50% date. In about half of springs, a 32°F night still comes after it.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

What does the 1 in 10 frost date mean?

It's NOAA's 10% date. In spring, a freeze still comes after it in about 1 year out of 10. In fall, the first freeze has already come before it in about 1 year out of 10.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

How accurate are last frost dates?

They're accurate as 30-year statistics for one station, 1991 to 2020. They can't tell you what this spring will do, and your yard can differ from the station.

Source: NOAA 1991-2020 U.S. Climate Normals, annual/seasonal, checked October 7, 2026.

Which weather station should I use for frost dates?

The one most like your yard: similar height, similar setting (city, open country, valley, near water), and close by. The frost date lookup shows the three nearest with their distance and height so you can compare.

Should I plant on the last frost date?

For tender plants, the later 1 in 10 date plus a clear forecast is the cautious choice. Hardy plants can go out around the typical date.

Source: NOAA 1991-2020 annual/seasonal normals documentation, checked October 7, 2026.

The arithmetic, done for you

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Sources

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