USDA zone 6a in Maine
USDA plant hardiness zone 6a covers 13 locations across Maine (average annual extreme minimum −10 to −5 °F): Blue Hill, ME, Blue Hill, ME, Brunswick, ME, Brunswick, ME, Cape Neddick, ME, Eastport, ME, and 7 more. Average last spring frost across this group ranges April 26 (Saco) to May 9 (Saco), and growing seasons run 146–178 days (Saco to Waldoboro) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Maine location's own frost dates; the printable planting calendar uses Saco, this group's median-season location.
- USDA zone
- 6a−10 to −5 °F
- Last frost range
- Apr 26–May 9avg, 32°F
- First frost range
- Oct 3–Oct 25avg, 32°F
- Growing season range
- 146–178days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Blue Hill | Bar Harbor, Winter Harbor, Milbridge, Southwest Harbor, Northeast Harbor | Acadia Np | Apr 27 | Oct 22 | 177 |
| Blue Hill | Castine | Belfast | May 7 | Oct 5 | 151 |
| Brunswick | Cumberland Center, Freeport, Cousins Island, Littlejohn Island | Gray | Apr 28 | Oct 19 | 172 |
| Brunswick | Bath, Boothbay Harbor | Wiscasset Ap | May 8 | Oct 7 | 151 |
| Cape Neddick | — | Cape Neddick | May 1 | Oct 14 | 165 |
| Eastport | Lubec | Eastport | Apr 29 | Oct 25 | 178 |
| Eastport | Machias | Robbinston | May 5 | Oct 13 | 160 |
| Machias | Milbridge, Jonesport | Jonesboro | May 3 | Oct 9 | 158 |
| Rockland | Camden, Thomaston | W Rockport 1 Nnw | Apr 27 | Oct 19 | 175 |
| Saco | Biddeford, Cape Neddick, North Berwick | Kennebunkport | May 9 | Oct 3 | 146 |
| Saco * | Portland, South Portland, Oak Hill, Falmouth, Falmouth Foreside, Littlejohn Island | Portland Intl Jetport | Apr 26 | Oct 15 | 170 |
| Waldoboro | Damariscotta, Boothbay Harbor | Newcastle | Apr 27 | Oct 18 | 172 |
| Waldoboro | Thomaston | Tenants Harbor | Apr 27 | Oct 25 | 178 |
* Saco is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Saco, representative)
Computed from Saco's average frost dates — the median-season location in this Mainezone 6a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 1 – Mar 15 | May 3 – May 10 | Jul 2 – Jul 22 | — | matures comfortably |
| Pepper | Very tender | Feb 15 – Mar 1 | May 10 – May 17 | Jul 9 – Aug 8 | — | matures comfortably |
| Cucumber | Tender | Mar 29 – Apr 5 | May 3 – May 10 | Jun 22 – Jul 12 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 3 – May 10 | Jun 17 – Jul 2 | — | matures comfortably |
| Bush bean | Tender | — | May 3 – May 10 | Jun 22 – Jul 2 | Aug 16 – Aug 26 | matures comfortably |
| Sweet corn | Tender | — | Apr 26 – May 10 | Jun 25 – Jul 25 | — | matures comfortably |
| Basil | Very tender | Mar 15 – Mar 29 | May 3 – May 10 | Jun 2 – Jun 17 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 15 – Mar 29 | Mar 29 – Apr 12 | May 13 – May 28 | Aug 2 – Aug 17 | matures comfortably |
| Pea | Hardy | — | Mar 15 – Mar 29 | May 9 – May 24 | Jul 23 – Aug 7 | matures comfortably |
| Spinach | Hardy | — | Mar 15 – Mar 29 | Apr 24 – May 4 | Aug 12 – Aug 22 | matures comfortably |
| Carrot | Half-hardy | — | Apr 5 – Apr 12 | Jun 4 – Jun 24 | Jul 13 – Aug 2 | matures comfortably |
| Broccoli | Half-hardy | Mar 1 – Mar 15 | Mar 29 – Apr 12 | May 23 – Jun 12 | Jul 18 – Aug 7 | matures comfortably |
Which crops fit this growing season
Using Saco's own 170-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Saco)
From NOAA's 1991–2020 Climate Normals at station USW00014764. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | May 7 | May 20 | Oct 4 | Oct 17 | 149 |
| 32°F (freeze) | Apr 26 | May 7 | Oct 15 | Oct 30 | 170 |
| 28°F | Apr 14 | Apr 25 | Oct 27 | Nov 9 | 195 |
| 24°F | Apr 3 | Apr 16 | Nov 8 | Nov 23 | 220 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 13 locations is 2,043; Saco's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 2,327 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,335 | cool-season crops (brassicas, greens) |
Hardiness zone 6a in Maine
Zone 6a means an average annual extreme minimum winter temperature of about −10 to −5 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Maine spans 8 hardiness zones in this dataset — see all Maine locations for the full range, including zones3b, 4a, 4b, 5a, 5b, 6b, 7a.
Explore zone 6a in other states at zone 6a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 6a mean in Maine?
- Zone 6a means an average annual extreme minimum winter temperature of −10 to −5 °F — the standard USDA measure of which perennials survive winter. 13 locations in Maine fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Maine's zone 6a is the growing season longest?
- Waldoboro runs the longest season on this page at about 178 days; Saco is shortest at about 146 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Maine's zone 6a?
- Using Saco's frost dates (this page's median-season location): start seeds indoors about Mar 1 – Mar 15, then transplant outside about May 3 – May 10. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Maine's zone 6a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 13 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.