Last Frost Date by ZIP Code: How to Find It and Use It

VNCNT Labs · Updated October 23, 2026 · 5 min read

Your last frost date decides almost every spring garden job: when to start seeds indoors, when to plant peas, and when it is finally safe to set out tomatoes. Here is what the date really means, how to look up the official number for your ZIP code, and how to turn it into a seed-starting calendar.

What a "last frost date" actually is

In the United States, frost dates come from NOAA's U.S. Climate Normals, which are 30-year statistics for thousands of weather stations. The current set covers 1991 to 2020 and is updated once a decade. For each station, NOAA's National Centers for Environmental Information (NCEI) calculates the date after which the chance of another freeze (an air temperature of 32°F or lower) drops below a given probability.

That last part matters. There isn't one last frost date. There are several, each tied to a level of risk:

• 90% date: there is still a 90% chance of a freeze after this day. Early and risky.
• 50% date (the median): the date most maps and seed packets call "the average last frost". After it, a freeze is less likely than not, but it is still a coin flip.
• 10% date: only a 1-in-10 chance of a later freeze. This is the safe date for tender plants.

The gap between them is often three to five weeks. The National Weather Service office in Wakefield, Virginia gives a clear example for Richmond International Airport: a 90% chance of still seeing a freeze after March 19, a median (50%) date of April 3, and only a 10% chance after April 18 (1991-2020 normals). Same station, same 30 years of data, a month apart.

How to find your last frost date by ZIP code

A ZIP code isn't a weather station, so every lookup works the same way: find the nearest station (or two) with frost normals and read its dates.

1. Go to the source. NCEI's Annual/Seasonal Normals (1991-2020) dataset publishes the freeze probabilities for each station. NOAA's Climate.gov explains how to pull them: open the Annual/Seasonal Normals page, choose your station, then under data types select the "probability date of last 32F occurrence" fields (10%, 50% and 90%) and preview the table.
2. Pick the right station. Choose one that is close and similar: same elevation band, same side of a ridge or lake. A station in a city center can run warmer than a valley garden a few miles away.
3. Note the 10%, 50% and 90% dates. Write all three down. You'll use different ones for different crops.
4. Adjust for your yard. Low spots collect cold air and frost later; south-facing walls and urban yards warm earlier. If you've gardened there a few years, trust your own notes too.

Some local NWS offices also publish 36°F "last potential frost" dates and 28°F "hard freeze" dates. Frost can form on plants when the air at thermometer height is a few degrees above freezing, which is why careful growers treat the 32°F dates as a minimum, not a guarantee.

Which date should you plan with?

• Frost-tender crops (tomatoes, peppers, eggplant, basil, squash, cucumbers, melons): plan around the 10% date, or at least one to two weeks after the 50% date. University of New Hampshire Extension lists tomatoes as safe to set out 1-2 weeks after the last frost, and peppers, eggplant, melons and squash about 2 weeks after.
• Hardy crops (peas, spinach, kale, cabbage, onions, lettuce): these go out before the last frost. UNH lists cabbage, kale, onions and leeks at about 4 weeks before, lettuce at 3-4 weeks before and broccoli at 2-4 weeks before.
• Somewhere in between: if a late cold snap would only cost you a few seedlings you can replace, the 50% date is a reasonable gamble. If it would cost a season, use the 10% date and keep a frost cloth handy.

Turn the date into a seed-starting calendar

Seed-starting dates are counted backwards from the day each crop goes into the garden, not from the frost date itself. First decide the transplant date (before or after frost, as above), then subtract the time the seedling needs indoors.

University of Maryland Extension gives slightly shorter indoor times for some crops (for example 5 to 6 weeks for tomatoes) and warns that sowing too early is one of the most common mistakes, because it produces tall, root-bound transplants. When two good sources differ, start with the shorter time if you grow under modest lights.

A worked example

Say your nearest station's 50% date is April 20 and its 10% date is May 4.

• Tomatoes: transplant around May 4 to 11 (after the 10% date). Count back 6 to 8 weeks: start seeds between March 9 and March 30.
• Peppers: transplant around May 4 (about 2 weeks after the 50% date). Count back 8 to 10 weeks: start seeds between February 23 and March 9.
• Broccoli: transplant around April 6 (2 weeks before the 50% date). Count back 4 to 6 weeks: start seeds between February 23 and March 9.
• Onions: transplant around March 23 (4 weeks before). Count back 8 to 10 weeks: start seeds between January 12 and January 26.

Before any transplant, harden seedlings off by giving them a little more outdoor time each day for about a week, so wind and sun don't shock them.

Don't forget the first fall frost

NOAA publishes first-freeze probabilities for autumn the same way. Count back from your first fall frost date using each crop's days to maturity to see whether a second sowing of beans, lettuce or broccoli will finish in time.

Frequently asked questions

Sources

1. NOAA Climate.gov: Interactive map, average date of last spring freeze
2. NOAA NCEI: U.S. Climate Normals (1991-2020)
3. NWS Wakefield, VA: Spring last freeze dates and probabilities (1991-2020)
4. University of New Hampshire Extension: When to plant your vegetable garden
5. University of Maryland Extension: Starting seeds indoors

More guides

• How Often to Water Houseplants (and Why a Fixed Schedule Fails)
• Home Maintenance Checklist: Monthly, Seasonal and Yearly Jobs
• Dog and Cat Vaccine Schedule: Puppies, Kittens and Adults