Last and first frost dates in Portland, Maine

When is the last frost in Portland, Maine?

The last frost in Portland, Maine usually comes around 15 April: that is the median of 2016–2025, so in about half of those years the last night at or below 0 °C came later. Hardy crops start before it and frost-tender ones only after it: in the table below arugula can go into open ground from 25 March, while corn waits until 18 May. The first autumn frost follows around 4 November, about 203 days later: harvest or cover frost-tender crops before then.

When to sow and plant

Planting out: a week after the last frost once the soil is warm enough for the crop; frost-hardy crops three weeks before it; an unheated greenhouse three weeks earlier. Seedlings are sown so they are ready on that day. Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.

What planting zone is Portland, Maine?

The official USDA map (2023, 1991–2020 data) puts the centre of Portland, Maine (ZIP 04101) in zone 6a. Zone 6a stands for an average coldest night of -10 to -5 °F (-23.3 to -20.6 °C), so perennials hardy to zone 6a or a colder zone should come through a typical winter here.

Check the official USDA map for Portland, Maine: USDA Plant Hardiness Zone Map.

When the soil warms up in Portland, Maine

The day the top 7 cm of soil first averages each temperature over a week, median of 2016–2025 (ERA5 via Open-Meteo). The soil reaches 10 °C 23 days after the last spring frost and 15 °C 43 days after it.

Frost dates near Portland, Maine

Of the nearest cities on our list, the last spring frost ends earliest in Boston (9 April) and latest in Bangor (24 April).

Seeds, seedlings and markets in Portland, Maine

Within 15 km of Portland, Maine OpenStreetMap lists 5 garden centres, 6 markets and 1 farm shop (collected 20 October 2026). The nearest garden centre to the city centre is Allen Sterling & Lothrop, 7 km away.

• Allen Sterling & Lothrop — garden centre
  Route 1 191, 04105 Falmouth · 7 km
• Public Market House — market
  Monument Square 28, 04101 Portland · 0 km
• Harmons Vegetable Stand — farm shop
  Spurwink Road 1, 04074 Scarborough · 12 km
• Skillins Greenhouses (Trees) — garden centre
  Mon–Fri 08:00–18:00; Sat 08:00–17:00; Sun 09:00–17:00 · 7 km
• Portland Farmer's Market — market
  Wed, Sat 07:00–13:00 · 1 km · portlandmainefarmersmarket.org
• Skillens Greenhouses — garden centre
  Mon–Fri 08:00–18:00; Sat 08:00–17:00; Sun 09:00–17:00 · 7 km

• Where to buy seeds and seedlings in Portland, Maine
• Selling your own harvest in the United States

Places: © OpenStreetMap contributors, ODbL.

Weather in Portland, Maine by month

Average weather in Portland, Maine over 2016–2025: the warmest month is July. Months that average 20 °C or more by day: June–September (21.7–26.1 °C). Nights average below 0 °C in December–March (-7.5–-3.2 °C). About 1171 mm of rain falls in a year, on 123 days; December is the wettest month (130 mm) and September the driest (80 mm).

Average of the daily highs and lows, rain per month and days with at least 1 mm (ERA5 via Open-Meteo, the same grid cell as the frost dates).

Planted in autumn

From a month before the first autumn frost, so the roots grow before winter, to the late-planting limit on each crop’s page (about two weeks before the ground freezes, by ten years of weather).