Miles, MT planting calendar
- USDA zone
- 4b−25 to −20 °F
- Last frost
- May 8avg, 32°F
- First frost
- Sep 30avg, 32°F
- Growing season
- 144days
Miles, Montana is in USDA plant hardiness zone 4b. Its average last spring frost is around May 8 and the first fall frost around September 30, giving a growing season of about 144 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.
Miles planting calendar
Each crop's windows are counted from Miles'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 13 – Mar 27 | May 15 – May 22 | Jul 14 – Aug 3 | — |
| Pepper | Very tender | Feb 27 – Mar 13 | May 22 – May 29 | Jul 21 – Aug 20 | — |
| Cucumber | Tender | Apr 10 – Apr 17 | May 15 – May 22 | Jul 4 – Jul 24 | — |
| Summer squash / zucchini | Tender | — | May 15 – May 22 | Jun 29 – Jul 14 | — |
| Bush bean | Tender | — | May 15 – May 22 | Jul 4 – Jul 14 | Aug 1 – Aug 11 |
| Sweet corn | Tender | — | May 8 – May 22 | Jul 7 – Aug 6 | — |
| Basil | Very tender | Mar 27 – Apr 10 | May 15 – May 22 | Jun 14 – Jun 29 | — |
| Lettuce | Half-hardy | Mar 27 – Apr 10 | Apr 10 – Apr 24 | May 25 – Jun 9 | Jul 18 – Aug 2 |
| Pea | Hardy | — | Mar 27 – Apr 10 | May 21 – Jun 5 | Jul 8 – Jul 23 |
| Spinach | Hardy | — | Mar 27 – Apr 10 | May 6 – May 16 | Jul 28 – Aug 7 |
| Carrot | Half-hardy | — | Apr 17 – Apr 24 | Jun 16 – Jul 6 | Jun 28 – Jul 18 |
| Broccoli | Half-hardy | Mar 13 – Mar 27 | Apr 10 – Apr 24 | Jun 4 – Jun 24 | Jul 3 – Jul 23 |
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 USW00024037. 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 18 | May 31 | Sep 23 | Oct 4 | 124 |
| 32°F (freeze) | May 8 | May 21 | Sep 30 | Oct 14 | 144 |
| 28°F | Apr 29 | May 12 | Oct 8 | Oct 23 | 163 |
| 24°F | Apr 17 | May 3 | Oct 18 | Oct 31 | 183 |
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) | 2,630 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,566 | cool-season crops (brassicas, greens) |
Hardiness zone 4b
Miles sits in USDA plant hardiness zone 4b on the 2023 map — meaning its average annual extreme minimum winter temperature is about −25 to −20 °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 4b, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Miles?
- Miles, Montana is in USDA plant hardiness zone 4b on the 2023 map (average annual extreme minimum temperature −25 to −20 °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 Miles?
- The average (median) last spring frost at 32°F is around May 8, 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 21, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Miles?
- The average first fall frost at 32°F is around September 30. That leaves a growing season of about 144 days between the average last spring and first fall frosts.
- When should I start tomatoes in Miles?
- Start tomato seeds indoors about Mar 13 – Mar 27 and transplant them outside about May 15 – May 22, once the danger of frost has passed. Estimated first harvest is around Jul 14 – Aug 3.
- How long is the growing season in Miles?
- About 144 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 8) and the average first fall frost (~September 30). 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 USW00024037 (Miles City F Wiley Fld, 7.5 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.