Poplar, MT planting calendar
- USDA zone
- 4a−30 to −25 °F
- Last frost
- May 24avg, 32°F
- First frost
- Sep 14avg, 32°F
- Growing season
- 110days
Poplar, Montana is in USDA plant hardiness zone 4a. Its average last spring frost is around May 24 and the first fall frost around September 14, giving a growing season of about 110 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.
Poplar planting calendar
Each crop's windows are counted from Poplar'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 29 – Apr 12 | May 31 – Jun 7 | Jul 30 – Aug 19 | — |
| Pepper | Very tender | Mar 15 – Mar 29 | Jun 7 – Jun 14 | Aug 6 – Sep 5 | — |
| Cucumber | Tender | Apr 26 – May 3 | May 31 – Jun 7 | Jul 20 – Aug 9 | — |
| Summer squash / zucchini | Tender | — | May 31 – Jun 7 | Jul 15 – Jul 30 | — |
| Bush bean | Tender | — | May 31 – Jun 7 | Jul 20 – Jul 30 | Jul 16 – Jul 26 |
| Sweet corn | Tender | — | May 24 – Jun 7 | Jul 23 – Aug 22 | — |
| Basil | Very tender | Apr 12 – Apr 26 | May 31 – Jun 7 | Jun 30 – Jul 15 | — |
| Lettuce | Half-hardy | Apr 12 – Apr 26 | Apr 26 – May 10 | Jun 10 – Jun 25 | Jul 2 – Jul 17 |
| Pea | Hardy | — | Apr 12 – Apr 26 | Jun 6 – Jun 21 | Jun 22 – Jul 7 |
| Spinach | Hardy | — | Apr 12 – Apr 26 | May 22 – Jun 1 | Jul 12 – Jul 22 |
| Carrot | Half-hardy | — | May 3 – May 10 | Jul 2 – Jul 22 | Jun 12 – Jul 2 |
| Broccoli | Half-hardy | Mar 29 – Apr 12 | Apr 26 – May 10 | Jun 20 – Jul 10 | Jun 17 – Jul 7 |
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 USW00094060. 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 | Jun 3 | Jun 24 | Sep 4 | Sep 16 | 90 |
| 32°F (freeze) | May 24 | Jun 6 | Sep 14 | Sep 25 | 110 |
| 28°F | May 14 | May 26 | Sep 22 | Oct 4 | 130 |
| 24°F | May 3 | May 15 | Sep 29 | Oct 13 | 147 |
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) | 1,888 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,599 | cool-season crops (brassicas, greens) |
Hardiness zone 4a
Poplar 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 Poplar?
- Poplar, Montana 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 Poplar?
- The average (median) last spring frost at 32°F is around May 24, 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 6, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Poplar?
- The average first fall frost at 32°F is around September 14. That leaves a growing season of about 110 days between the average last spring and first fall frosts.
- When should I start tomatoes in Poplar?
- Start tomato seeds indoors about Mar 29 – Apr 12 and transplant them outside about May 31 – Jun 7, once the danger of frost has passed. Estimated first harvest is around Jul 30 – Aug 19.
- How long is the growing season in Poplar?
- About 110 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 24) and the average first fall frost (~September 14). 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 USW00094060 (Wolf Point 29 Ene, 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.