Caribou, ME planting calendar
- USDA zone
- 4a−30 to −25 °F
- Last frost
- May 7avg, 32°F
- First frost
- Oct 1avg, 32°F
- Growing season
- 143days
Caribou, Maine is in USDA plant hardiness zone 4a. Its average last spring frost is around May 7 and the first fall frost around October 1, giving a growing season of about 143 days (NOAA 1991–2020 normals, 32°F, median). Start tender crops like tomatoes and peppers indoors weeks before the last frost and set them out afterward; sow hardy crops such as peas, spinach, and lettuce before it. The planner below turns those frost dates into a printable per-crop planting calendar.
Caribou planting calendar
Each crop's windows are counted from Caribou's average frost dates. 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.
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting |
|---|---|---|---|---|---|
| Tomato | Tender | Mar 12 – Mar 26 | May 14 – May 21 | Jul 13 – Aug 2 | — |
| Pepper | Very tender | Feb 26 – Mar 12 | May 21 – May 28 | Jul 20 – Aug 19 | — |
| Cucumber | Tender | Apr 9 – Apr 16 | May 14 – May 21 | Jul 3 – Jul 23 | — |
| Summer squash / zucchini | Tender | — | May 14 – May 21 | Jun 28 – Jul 13 | — |
| Bush bean | Tender | — | May 14 – May 21 | Jul 3 – Jul 13 | Aug 2 – Aug 12 |
| Sweet corn | Tender | — | May 7 – May 21 | Jul 6 – Aug 5 | — |
| Basil | Very tender | Mar 26 – Apr 9 | May 14 – May 21 | Jun 13 – Jun 28 | — |
| Lettuce | Half-hardy | Mar 26 – Apr 9 | Apr 9 – Apr 23 | May 24 – Jun 8 | Jul 19 – Aug 3 |
| Pea | Hardy | — | Mar 26 – Apr 9 | May 20 – Jun 4 | Jul 9 – Jul 24 |
| Spinach | Hardy | — | Mar 26 – Apr 9 | May 5 – May 15 | Jul 29 – Aug 8 |
| Carrot | Half-hardy | — | Apr 16 – Apr 23 | Jun 15 – Jul 5 | Jun 29 – Jul 19 |
| Broccoli | Half-hardy | Mar 12 – Mar 26 | Apr 9 – Apr 23 | Jun 3 – Jun 23 | Jul 4 – Jul 24 |
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.
Frost & freeze dates
From NOAA's 1991–2020 Climate Normals at station USW00014607. 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 (p10 for spring, p90 for fall) — 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 24 | Jun 7 | Sep 19 | Oct 1 | 117 |
| 32°F (freeze) | May 7 | May 24 | Oct 1 | Oct 14 | 143 |
| 28°F | Apr 26 | May 7 | Oct 12 | Oct 30 | 167 |
| 24°F | Apr 17 | Apr 27 | Oct 29 | Nov 10 | 193 |
32°F is the standard "freeze" line that damages tender crops; lighter 36°F frost can nip the most cold-sensitive plants, while hardy crops shrug off light frost down toward 28°F. Use the threshold that matches what you are protecting.
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. Warm-season crops need a long, warm GDD total; a short, cool GDD total favors greens and brassicas.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 1,726 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,418 | cool-season crops (brassicas, greens) |
Hardiness zone 4a
Caribou sits in USDA plant hardiness zone 4a on the 2023 map — meaning its average annual extreme minimum winter temperature is about −30 to −25 °F. That number 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.
Explore more places in zone 4a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Caribou?
- Caribou, Maine is in USDA plant hardiness zone 4a on the 2023 map (average annual extreme minimum temperature −30 to −25 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.
- When is the last frost in Caribou?
- The average (median) last spring frost at 32°F is around May 7, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as May 24, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Caribou?
- The average first fall frost at 32°F is around October 1. That leaves a growing season of about 143 days between the average last spring and first fall frosts.
- When should I start tomatoes in Caribou?
- Start tomato seeds indoors about Mar 12 – Mar 26 and transplant them outside about May 14 – May 21, once the danger of frost has passed. Estimated first harvest is around Jul 13 – Aug 2.
- How long is the growing season in Caribou?
- About 143 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 7) and the average first fall frost (~October 1). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020 for station USW00014607 (Caribou Muni Ap, 4.6 km away). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to this 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.