Plymouth, NH 03245 planting calendar
- USDA zone
- 5b−15 to −10 °F
- Last frost
- May 20avg, 32°F
- First frost
- Sep 27avg, 32°F
- Growing season
- 128days
Plymouth, New Hampshire is in USDA plant hardiness zone 5b. Its average last spring frost is around May 20 and the first fall frost around September 27, giving a growing season of about 128 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.
Plymouth planting calendar
Each crop's windows are counted from Plymouth'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 25 – Apr 8 | May 27 – Jun 3 | Jul 26 – Aug 15 | — |
| Pepper | Very tender | Mar 11 – Mar 25 | Jun 3 – Jun 10 | Aug 2 – Sep 1 | — |
| Cucumber | Tender | Apr 22 – Apr 29 | May 27 – Jun 3 | Jul 16 – Aug 5 | — |
| Summer squash / zucchini | Tender | — | May 27 – Jun 3 | Jul 11 – Jul 26 | — |
| Bush bean | Tender | — | May 27 – Jun 3 | Jul 16 – Jul 26 | Jul 29 – Aug 8 |
| Sweet corn | Tender | — | May 20 – Jun 3 | Jul 19 – Aug 18 | — |
| Basil | Very tender | Apr 8 – Apr 22 | May 27 – Jun 3 | Jun 26 – Jul 11 | — |
| Lettuce | Half-hardy | Apr 8 – Apr 22 | Apr 22 – May 6 | Jun 6 – Jun 21 | Jul 15 – Jul 30 |
| Pea | Hardy | — | Apr 8 – Apr 22 | Jun 2 – Jun 17 | Jul 5 – Jul 20 |
| Spinach | Hardy | — | Apr 8 – Apr 22 | May 18 – May 28 | Jul 25 – Aug 4 |
| Carrot | Half-hardy | — | Apr 29 – May 6 | Jun 28 – Jul 18 | Jun 25 – Jul 15 |
| Broccoli | Half-hardy | Mar 25 – Apr 8 | Apr 22 – May 6 | Jun 16 – Jul 6 | Jun 30 – Jul 20 |
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 USC00276945. 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 31 | Jun 13 | Sep 15 | Sep 28 | 107 |
| 32°F (freeze) | May 20 | Jun 4 | Sep 27 | Oct 7 | 128 |
| 28°F | May 7 | May 24 | Oct 6 | Oct 22 | 151 |
| 24°F | Apr 23 | May 9 | Oct 19 | Nov 6 | 178 |
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) | 1,837 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,625 | cool-season crops (brassicas, greens) |
Hardiness zone 5b
Plymouth sits in USDA plant hardiness zone 5b on the 2023 map — meaning its average annual extreme minimum winter temperature is about −15 to −10 °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 5b, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Plymouth?
- Plymouth, New Hampshire is in USDA plant hardiness zone 5b on the 2023 map (average annual extreme minimum temperature −15 to −10 °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 Plymouth?
- The average (median) last spring frost at 32°F is around May 20, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as June 4, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Plymouth?
- The average first fall frost at 32°F is around September 27. That leaves a growing season of about 128 days between the average last spring and first fall frosts.
- When should I start tomatoes in Plymouth?
- Start tomato seeds indoors about Mar 25 – Apr 8 and transplant them outside about May 27 – Jun 3, once the danger of frost has passed. Estimated first harvest is around Jul 26 – Aug 15.
- How long is the growing season in Plymouth?
- About 128 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 20) and the average first fall frost (~September 27). 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 USC00276945 (Plymouth, 5.9 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.