Frost dates Massachusetts Worcester

Frost dates in Worcester, Massachusetts

Last spring frost Apr 23 First fall frost Oct 21 NOAA 1991-2020

The average last spring frost in Worcester is Apr 23 and the average first fall frost is Oct 21, measured at WORCESTER RGNL AP, about 4 miles from the city centre. Below: how sure those dates are, and what to start, sow and set out each week.

Average last spring frostApr 2332°F, 50% probability
Average first fall frostOct 2132°F, 50% probability
Days between them181average frost-free season
How sure is that date? NOAA probability levels for a 32°F freeze
ProbabilityFreeze still comes after (spring)First freeze has come by (fall)
90%Apr 11Nov 3
50%Apr 23Oct 21
10%May 5Oct 6

Read it like this: in half of years the last 32°F freeze of spring comes after Apr 23, and in 1 year in 10 there is still a freeze after May 5. In 1 year in 10 the first fall freeze arrives before Oct 6.

Measured at: WORCESTER RGNL AP, MA (NOAA station USW00094746), about 4 miles away at 1,000 ft, 28 years of record in 1991-2020.

Other stations nearby, for comparison:

  • BUFFUMVILLE LAKE, MA (NOAA station USC00190998), about 11 miles away at 520 ft, 25 years of record in 1991-2020: last spring frost May 1, first fall frost Oct 10
  • BARRE FALLS DAM, MA (NOAA station USC00190408), about 16 miles away at 825 ft, 19 years of record in 1991-2020: last spring frost May 12, first fall frost Oct 1

Seed-starting schedule for Worcester, MA

Counted from a last frost date of Apr 23 (the average: a freeze comes later than this in half of years).

  1. Week of Jan 1514 weeks before last frost
    • Start seeds indoorsLeekJan 15 to Jan 29
    • Start seeds indoorsOnionJan 15 to Jan 29
  2. Week of Jan 2213 weeks before last frost
    • Start seeds indoorsParsleyJan 22 to Jan 29
  3. Week of Jan 2912 weeks before last frost
    • Start seeds indoorsCeleryJan 29 to Feb 12
    • Start seeds indoorsSpinachJan 29 to Feb 12
  4. Week of Feb 1210 weeks before last frost
    • Start seeds indoorsBroccoliFeb 12 to Feb 26
    • Start seeds indoorsBrussels sproutFeb 12 to Feb 26
    • Start seeds indoorsCabbageFeb 12 to Feb 26
    • Start seeds indoorsKaleFeb 12 to Feb 26
    • Start seeds indoorsKohlrabiFeb 12 to Feb 26
  5. Week of Feb 199 weeks before last frost
    • Start seeds indoorsLettuceFeb 19 to Feb 26
  6. Week of Feb 268 weeks before last frost
    • Start seeds indoorsCauliflowerFeb 26 to Mar 12
    • Start seeds indoorsEggplantFeb 26 to Mar 12
    • Start seeds indoorsPepperFeb 26 to Mar 12
    • Start seeds indoorsSwiss chardFeb 26 to Mar 12
  7. Week of Mar 57 weeks before last frost
    • Start seeds indoorsTomatoMar 5 to Mar 19
  8. Week of Mar 126 weeks before last frost
    • Start seeds indoorsBasilMar 12 to Mar 26
    • Set transplants outSpinachMar 12 to Apr 2
  9. Week of Mar 264 weeks before last frost
    • Sow seed outdoorsRadishMar 26 to Apr 9
    • Sow seed outdoorsSwiss chardfrom Mar 26
    • Sow seed outdoorsTurnipMar 26 to Apr 9
    • Set transplants outBroccoliMar 26 to Apr 9
    • Set transplants outBrussels sproutMar 26 to Apr 9
    • Set transplants outCabbagefrom Mar 26
    • Set transplants outKalefrom Mar 26
    • Set transplants outKohlrabifrom Mar 26
    • Set transplants outLeekfrom Mar 26
    • Set transplants outLettuceMar 26 to Apr 2
    • Set transplants outOnionfrom Mar 26
  10. Week of Apr 23 weeks before last frost
    • Start seeds indoorsCucumberApr 2 to Apr 9
    • Set transplants outParsleyApr 2 to Apr 9
  11. Week of Apr 92 weeks before last frost
    • Start seeds indoorsMelonApr 9 to Apr 16
    • Start seeds indoorsPumpkinApr 9 to Apr 16
    • Start seeds indoorsSummer squashApr 9 to Apr 16
    • Start seeds indoorsWinter squashApr 9 to Apr 16
    • Start seeds indoorsZucchiniApr 9 to Apr 16
    • Plant seed potatoes outdoorsPotatoApr 9 to Apr 16
    • Set transplants outCauliflowerfrom Apr 9
    • Set transplants outSwiss chardfrom Apr 9
  12. Week of Apr 23Last frost week
    • Sow seed outdoorsBeanfrom Apr 23
    • Sow seed outdoorsParsnipfrom Apr 23
    • Set transplants outCeleryfrom Apr 23
  13. Week of Apr 301 week after last frost
    • Plant slips outdoorsSweet potatoApr 30 to May 7
    • Set transplants outCucumberApr 30 to May 7
    • Set transplants outTomatoApr 30 to May 7
  14. Week of May 72 weeks after last frost
    • Set transplants outBasilfrom May 7
    • Set transplants outEggplantMay 7 to May 14
    • Set transplants outMelonfrom May 7
    • Set transplants outPepperfrom May 7
    • Set transplants outPumpkinfrom May 7
    • Set transplants outSummer squashfrom May 7
    • Set transplants outWinter squashfrom May 7
    • Set transplants outZucchinifrom May 7

Not in the city centre? Look up your own ZIP code

More in Massachusetts

Where the numbers come from

Sources and method

Frost dates. U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), NOAA National Centers for Environmental Information (Palecki, Durre, Applequist, Arguez and Lawrimore, 2021). These are 30-year station statistics for 1991 to 2020. "Frost" here means an air temperature of 32°F or lower at the station. We use 6,539 stations that have at least 10 years of record and a published date; 176 more are stations where a freeze is too rare for NOAA to date, and 180 are stations cold enough to have frost risk all year.

Probability level. The headline dates are NOAA's 50% level: in half of years the last spring freeze comes later than that date, and in half of years the first fall freeze comes earlier. The 10% and 90% levels are shown next to them. For tender plants, the 10% spring date is the safer one to plan from: a freeze follows it in only 1 year in 10.

Which station. Your ZIP code is matched to the nearest of those stations by straight-line distance from the ZIP code's centre point (GeoNames, geonames.org, CC BY 4.0; 40,979 ZIP codes in the 50 states and DC). Nearest is not always most alike: a station on a hill, in a valley or by the water can differ from your garden by a week or more. That is why the station's name, distance and elevation are shown with every result, along with two more stations nearby. NOAA makes the same point: the normals are limited between stations as distance grows horizontally and vertically.

Seed-starting offsets. Growing Vegetables: When to Plant Your Vegetable Garden, a fact sheet from University of New Hampshire Extension. It gives each crop's weeks from seed to transplant and when it is safe to set out or sow relative to the last frost. The method is theirs too: take the planting date and count back the seed-to-transplant weeks. Where the fact sheet gives a range of planting dates, the start-indoors dates count back from the earliest one. The figures used, as the fact sheet states them:

  • Basil: Seed to transplant 6-8 weeks; set out 2 weeks after last frost.
  • Bean: Plant seed in garden after last frost.
  • Broccoli: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Brussels sprout: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Cabbage: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Cauliflower: Seed to transplant 4-6 weeks; set out 2 weeks before last frost.
  • Celery: Seed to transplant 10-12 weeks; set out after last frost.
  • Cucumber: Seed to transplant 3-4 weeks; set out 1-2 weeks after last frost.
  • Eggplant: Seed to transplant 8-10 weeks; set out 2-3 weeks after last frost.
  • Kale: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Kohlrabi: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Leek: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Lettuce: Seed to transplant 4-5 weeks; set out 3-4 weeks before last frost.
  • Melon: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Onion: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Parsley: Seed to transplant 9-10 weeks; set out 2-3 weeks before last frost.
  • Parsnip: Plant seed in garden after last frost.
  • Pepper: Seed to transplant 8-10 weeks; set out 2 weeks after last frost.
  • Potato: Plant seed potatoes in garden 1-2 weeks before last frost.
  • Pumpkin: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Radish: Plant seed in garden 2-4 weeks before last frost.
  • Spinach: Seed to transplant 4-6 weeks; set out 3-6 weeks before last frost.
  • Summer squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Sweet potato: Plant slips in garden 1-2 weeks after last frost.
  • Swiss chard: Seed to transplant 4-6 weeks; set out 2 weeks before last frost; or plant seed in garden 4 weeks before last frost.
  • Tomato: Seed to transplant 6-8 weeks; set out 1-2 weeks after last frost.
  • Turnip: Plant seed in garden 2-4 weeks before last frost.
  • Winter squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Zucchini: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.

Not on the calendar. The same fact sheet times these by soil temperature, not by frost date, so they get no date here:

  • Pea: as soon as the soil thaws.
  • Beet: when the soil warms to 45°F.
  • Carrot: when the soil warms to 60°F.
  • Corn: when the soil warms to 60°F.
  • Cucumber, pumpkin, summer squash, winter squash, zucchini: direct-sow when the soil warms to 70°F.

Rutabaga is left out: the fact sheet gives it New Hampshire calendar dates, not a frost offset.

The fact sheet was written for New Hampshire. The offsets are relative to the last frost, so they carry to other places with a spring frost, but where winters are mild many cool-season crops are grown in fall and winter instead. Your state's extension service has the local calendar. Dates are 30-year statistics, not a forecast: check the forecast before setting tender plants out.

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