When to plant in South Portland, ME
USDA Zone 6aSouth Portland, Maine frost dates, USDA zone, and a full-year planting calendar, drawn from the nearest NOAA station and tuned to the local season.
Zone 6a means South Portland sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
The average last spring frost in South Portland is now 5 days earlier than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
PORTLAND INTL JETPORT · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are South Portland’s own odds, recorded at PORTLAND INTL JETPORT.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 20 | May 7 | Apr 28 | Sep 24 | Oct 4 | Oct 17 |
| 32°F | May 7 | Apr 26 | Apr 16 | Oct 2 | Oct 15 | Oct 30 |
| 28°F | Apr 25 | Apr 14 | Apr 3 | Oct 14 | Oct 27 | Nov 9 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in South Portland, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 29 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
South Portland planting FAQ
When is the last spring frost in South Portland, ME?
South Portland's average last spring frost falls near April 26 — the 50% mark at 32°F in the 1991–2020 normals. Hold tender transplants until the risk has passed, then plant out.
When is the first fall frost in South Portland, ME?
Expect South Portland's first fall frost near October 15 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is South Portland in?
South Portland is in USDA hardiness zone 6a. In zone 6a, winters are moderate — most common vegetables grow well in season.
How long is the growing season in South Portland?
There are roughly 172 frost-free days in South Portland (a moderate growing season), running from the average last frost around April 26 to the first fall frost near October 15.
When should I plant tomatoes in South Portland?
In South Portland, start tomato seeds indoors around March 1–March 15, then transplant seedlings outdoors around May 3 once the danger of frost has passed.
Never miss a window in South Portland
An email when it’s time to start seeds, transplant, and sow — timed to South Portland’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reachFrost dates recorded at PORTLAND INTL JETPORT, 2 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in South Portland, ME — Frost Dates & Zone 6a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00014764. Retrieved from https://blissgarden.com/maine/south-portland.