Frost dates for Portland, Maine
In Portland, half of springs have had their last frost by April 26 (and 1 spring in 10 still has one after May 7), and half of falls have had their first frost by October 15, leaving about 170 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Portland, Maine
Last spring frost
April 26
Half of springs have their last frost by this date. For a safer bet, wait until May 7: only 1 spring in 10 has a frost after that.
First fall frost
October 15
Half of falls have their first frost by this date. In 1 fall in 10 it comes by October 2.
Growing season
170 days
Frost-free days in a typical year. 9 years in 10 get at least 153.
Hardiness zone
6a
2023 USDA map: the coldest night of winter averages −10°F to −5°F. On the 2012 map it was 5b, half a zone colder. All 8 ZIP codes within about 6 miles of the city's center are in zone 6a.
Print a year planner for Portland
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | April 16 | April 26 | May 7 |
| First frost in fall | October 2 | October 15 | October 30 |
The frost-free season between them runs 170 days in a typical year. In 1 year in 10 it is 188 days or longer, and in 1 year in 10 it is 153 days or shorter.
- Hard freeze (28°F): typically last on April 14 and first on October 27. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on May 7 and first on October 4. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Portland comes between April 16 and May 7, a window of 21 days. That is narrower than at most NOAA stations (the typical window is 31 days), so the typical date is a steadier guide here than in most places.
Among Maine's 82 NOAA stations with a frost every year, 96 percent have their typical last frost later than Portland does.
Planting calendar for Portland
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
| When | What to do | Why then |
|---|---|---|
| February | ||
| February 8 to March 8 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February 22 to March 22 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March | ||
| March 8 to 29 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 15 to 29 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 22 to April 5 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| March 29 to April 12 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| March 29 to April 12 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April | ||
| April 12 to 26 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 12 to 26 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| April 26 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May | ||
| May 10 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 10 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| May 20 to June 3 | Cabbage for fall Start seeds | set the plants out by July 8 |
| June | ||
| June 9 to 23 | Broccoli for fall Start seeds | set the plants out by July 28 |
| July | ||
| July 19 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 23 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 24 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 28 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 29 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August | ||
| August 2 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August 12 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 22 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 1 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| October | ||
| October 2 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| November | ||
| November 3 to 10 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 11 days later. That plans around May 7, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Portland International Jetport (station USW00014764), 6 miles from the center of Portland. It sits at about the same elevation, 50 feet above sea level. NOAA rates this station's record as standard: at least 24 of the 30 years, with gaps filled from nearby stations.
The same station also gives the frost dates for South Portland, Westbrook and Saco.
Our ZIP code lookup matches these 18 ZIP codes to the same station, so they get the same dates: 04017, 04019, 04021, 04050, 04064, 04072, 04074, 04092, 04096, 04101, 04102, 04103, 04105, 04106, 04107, 04108, 04109, 04110. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Lewiston, Maine: last frost around April 25, first frost around October 19 (30 miles away)
- Concord, New Hampshire: last frost around May 8, first frost around October 3 (75 miles away)
- Manchester, New Hampshire: last frost around April 21, first frost around October 19 (80 miles away)
See frost dates across Maine, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.