Boston, Massachusetts Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Boston?

The typical last 32°F night is Apr 4, and in 1 year out of 10 a freeze still comes after Apr 17. Cold 36°F nights (frost possible on plants) typically last longer, to around Apr 17. The last hard freeze (28°F) typically comes earlier, around Mar 28.

There are 13 days between the typical date (Apr 4) and the safer 1-in-10 date (Apr 17). Planting in that stretch is a gamble, so keep an eye on the 10-day forecast.

Cool nights hang on after the last freeze: the typical last 36°F night (frost possible on plants in low spots) is around Apr 17, 13 days later than the typical last 32°F night. Frost can form on leaves on clear, calm nights even with the thermometer above freezing.

These dates come from the station with the earliest typical last frost among the 15 eligible stations near Boston. If your yard sits in a cooler spot, lean toward Apr 17.

Is it too early to plant in Boston?

Before Apr 4 the odds of another 32°F night are better than even; after Apr 17 they are about 1 in 10 or less.

Today's risk is computed in your browser from the same NOAA probability table, shown as the range between the two nearest NOAA probability levels.

When is the first frost in Boston?

By Nov 9, half of years have had their first 32°F night. In 1 year out of 10, it comes as early as Oct 29. In a typical year, look for the first 36°F night (frost possible on plants) around Oct 29 and the first 28°F hard freeze around Nov 21.

To time a fall crop, count back from the typical first frost (Nov 9) or the safer Oct 29. The planting calendar works it out crop by crop.

How long is Boston's growing season?

A typical year in Boston has 218 days between the last spring and first fall 32°F nights. In about 1 year in 10, there are fewer than 201 days.

Most warm-season vegetables have time to finish if you plant on schedule. For long-season crops, transplants do best.

Each year the station logs an average of 3,050 growing degree days (base 50°F), a measure of the heat available for crop growth.

How does Boston's season compare?

Among the 56 U.S. cities with frost dates on this site, the typical frost-free season here is longer than in 31 of them and shorter than in 24.

Growing degree days (base 50°F)

Annual normal: 3,050 GDD (NOAA flag S, 27 years). Running total by the end of each month (sum of NOAA daily GDD normals, so the year-end total can differ slightly from the annual normal):

What growing zone is Boston? (USDA 2023)

The 2023 USDA map puts Boston in zone 6b–7a (-5 to 5°F average coldest winter night). On the 2012 map, most of the city was 6b. Comparing ZIPs listed in both tables, 16 of 31 moved up half a zone.

Zones: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 2026-10-08. Shown as published in the ZIP tables; this page does not show a zone map. Not the official USDA Plant Hardiness Zone Map (official map: planthardiness.ars.usda.gov).

Does the new zone change Boston's frost dates?

No. A hardiness zone reflects only the average coldest winter temperature, not the timing of spring or fall frost. Boston's frost dates come from NOAA's 1991–2020 frost probabilities, and the 2023 zone map didn't change them. Pick perennials that survive winter by zone; time your planting by frost dates.

Why do Boston frost dates differ between websites?

Some sources list Apr 8 for Boston. That's the 30%-risk date: about 3 years in 10 still see a 32°F night after it. We headline the 50% (median) date, Apr 4.

Apr 17 is the date we call 'safer': it's the 10%-risk date, with a 32°F night after it in only about 1 year in 10.

Apr 17 is the typical (50%) date for a 36°F night (frost possible on plants), not a 32°F freeze. Any site that draws the line at 36°F will show later dates.

The choice of weather station matters too. The 15 stations within 25 miles of the city center that pass our quality rules give typical (50%) last 32°F frost dates from Apr 4 to May 4; see the table below.

Which weather station is this based on?

Station

Boston Logan International Airport (NOAA USW00014739, WBAN/ASOS-AWOS)

Distance

1.6 mi NNE of the city center

Elevation

12 ft; city center 5 ft (USGS), difference +7 ft

Record

NOAA completeness flag S, 28 of 30 years (1991–2020)

Confidence

High (rule)

Confidence: High. At 1.6 miles from the city center and only 7 ft off in elevation, with frost statistics that meet our completeness rule (NOAA flag S, 28 of 30 years), this station is a close match.

Boston planting dates at a glance

Balanced dates use the 30%-risk last-frost date as the anchor. The Boston planting calendar has typical and safe dates, fall planting and a month-by-month list for 26 vegetables.

When to plant tomatoes in Boston · Fall planting dates for Boston

Frost dates near Boston

All Massachusetts cities

Frequently asked questions

What is the average last frost date in Boston?

Apr 4 is the median (50%) date for Boston's last 32°F night, from NOAA 1991–2020 normals at Boston Logan International Airport. To play it safe, use Apr 17: only about 1 year in 10 has a freeze after it.

When is the first frost in Boston?

Expect the first 32°F night by Nov 9 in a typical year, and as early as Oct 29 in about 1 year out of 10. Cold 36°F nights (frost possible on plants) typically start around Oct 29.

What growing zone is Boston, Massachusetts?

On the 2023 USDA map, Boston is in hardiness zone 6b–7a. Most of it was 6b on the 2012 map as well; 16 of the 31 city ZIPs listed in both tables changed zone.

Is it too early to plant in Boston?

Before Apr 4, yes, for anything frost-tender. Until then, the odds of another 32°F night are better than even. The risk falls from 50% to 10% between Apr 4 and Apr 17. Peas, lettuce and other cool-season crops can go in weeks earlier; the planting calendar has dates.

What temperature is a killing frost?

A light frost is enough to kill tender crops such as tomatoes. CSU Extension describes 28–32°F as a light frost and anything below 28°F as a heavy frost. We report NOAA odds at three thresholds: 36°F (frost possible on plants), 32°F (freeze, our headline) and 28°F (hard freeze).

Is first frost the same as first freeze?

Not quite. A 'freeze' means the air reached 32°F. 'Frost' is ice on surfaces, and it can form on calm, clear nights even when the air is a few degrees above freezing. So in Boston, the first 36°F night (frost possible on plants) typically comes around Oct 29, before the first 32°F night (Nov 9).

Download & sources

• Add Boston frost & planting dates to your calendar (.ics, 2027)
• Printable planting calendar (PDF)
• How these numbers are calculated

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal and daily normals, station USW00014739); USDA Plant Hardiness Zone ZIP tables 2023 and 2012 by the PRISM Group, Oregon State University; Census 2020 ZIP/place relationship file; USGS elevation. Long-term odds, not a forecast. Figures and sentences are generated from these data by fixed rules; see the methodology. Last updated 2026-10-08.