Portland, Maine: planting zone & frost dates
Portland is in USDA plant hardiness zone 6a, where the average coldest winter night reaches -10 to -5°F (-23.3 to -20.6°C). The typical last spring frost is around May 1 and the first fall frost around Oct 9.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 7 | Oct 2 |
| Typical planning date (30% risk) | May 1 | Oct 9 |
| Median (50%) | Apr 26 | Oct 15 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station PORTLAND INTL JETPORT, ME (USW00014764), 5.8 mi (9.4 km) from the city center and 46 ft higher than the city center (+14 m). Record used for the 1991–2020 normals: 30 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Portland
All 6 ZIP codes covering Portland are in zone 6a.
Vegetable planting calendar for Portland
Dates are counted from the 30%-risk frost dates above (last frost May 1, first frost Oct 9). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 6 – Mar 20 | May 8 – May 22 | — | — |
| Pepper | Feb 20 – Mar 6 | May 15 – May 29 | — | — |
| Lettuce | Mar 20 – Apr 3 | Apr 17 – May 8 | Apr 3 – May 15 | Jul 31 – Aug 28 |
| Green Beans | — | — | May 8 – Jun 12 | Jul 17 – Jul 31 |
| Sweet Corn | — | — | May 8 – Jun 5 | — |
| Zucchini & Summer Squash | Apr 3 – Apr 10 | May 8 – May 22 | May 8 – May 29 | Jul 17 – Jul 31 |
| Cucumber | Apr 3 – Apr 10 | May 15 – May 22 | May 8 – May 29 | Jul 17 – Jul 31 |
| Carrot | — | — | Apr 10 – May 15 | Jul 17 – Jul 31 |
| Onion | Feb 6 – Feb 20 | Apr 3 – Apr 17 | — | — |
| Potato | — | Apr 3 – Apr 24 | — | — |
| Basil | Mar 20 – Apr 3 | May 15 – May 29 | May 15 – Jun 5 | — |
| Spinach | — | — | Mar 20 – Apr 17 | Aug 14 – Sep 11 |
| Kale | Mar 6 – Mar 20 | Apr 3 – Apr 24 | Apr 3 – Apr 24 | Jul 31 – Aug 28 |
| Broccoli | Mar 6 – Mar 20 | Apr 17 – May 8 | — | Jul 17 – Jul 31 |
| Peas | — | — | Mar 20 – Apr 10 | Jul 31 – Aug 14 |
| Eggplant | Feb 20 – Mar 6 | May 15 – May 29 | — | — |
| Cabbage | Mar 6 – Mar 20 | Apr 3 – Apr 17 | — | Jul 17 – Jul 31 |
| Radish | — | — | Mar 27 – May 15 | Aug 28 – Sep 25 |
| Strawberry | — | Apr 3 – Apr 24 | — | — |
| Beets | — | — | Apr 10 – May 22 | Jul 31 – Aug 14 |
Nearby cities in Maine
- Lewiston — zone 5b, last frost Apr 30, first frost Oct 13
More: all Maine cities · other zone 6a cities: Chicago, IL, Denver, CO, Milwaukee, WI, Colorado Springs, CO, Omaha, NE, Aurora, CO, Lincoln, NE, Fort Wayne, IN
Portland gardening questions
When is the last frost in Portland, ME?
Plan around May 1. At NOAA's Portland Int'l Jetport, ME station, 5.8 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 26, and after May 7 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 14. The last frost is fairly predictable here: only 21 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Portland, ME?
Start seeds indoors Mar 6 – Mar 20 and set transplants outside May 8 – May 22, once nights stay above 50°F and the soil is near 60°F. That leaves 161 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Portland?
About 170 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 153 days, and in 1 year in 10 it runs 188 days or more. In fall there is a 10% chance of frost by Oct 2 and a 30% chance by Oct 9.
When should I plant a fall garden in Portland?
Count back from the first fall frost (Oct 9): transplant broccoli Jul 17 – Jul 31; sow kale Jul 31 – Aug 28; sow lettuce Jul 31 – Aug 28; sow radishes Aug 28 – Sep 25. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 27. How the math works: succession and fall planting.
Did Portland's hardiness zone change on the 2023 map?
Yes. Most of Portland was zone 5b on the 2012 map and is zone 6a on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
How does Portland compare with Lewiston, ME?
Portland is zone 6a and Lewiston is zone 5b. The typical last spring frost in Portland (May 1) comes about the same time as in Lewiston, ME (Apr 30), 32 miles away, and the first fall frost is Oct 9 versus Oct 13. Portland sits about 299 ft lower, which explains part of the gap. The two cities use different NOAA stations.