Butte-Silver Bow, MT 59701 planting calendar
- USDA zone
- 5a−20 to −15 °F
- Last frost
- Jun 13avg, 32°F
- First frost
- Sep 5avg, 32°F
- Growing season
- 83days
Butte-Silver Bow, Montana is in USDA plant hardiness zone 5a. Its average last spring frost is around June 13 and the first fall frost around September 5, giving a growing season of about 83 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.
Butte-Silver Bow planting calendar
Each crop's windows are counted from Butte-Silver Bow'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 | Apr 18 – May 2 | Jun 20 – Jun 27 | Aug 19 – Sep 8 | — |
| Pepper | Very tender | Apr 4 – Apr 18 | Jun 27 – Jul 4 | Aug 26 – Sep 25 | — |
| Cucumber | Tender | May 16 – May 23 | Jun 20 – Jun 27 | Aug 9 – Aug 29 | — |
| Summer squash / zucchini | Tender | — | Jun 20 – Jun 27 | Aug 4 – Aug 19 | — |
| Bush bean | Tender | — | Jun 20 – Jun 27 | Aug 9 – Aug 19 | Jul 7 – Jul 17 |
| Sweet corn | Tender | — | Jun 13 – Jun 27 | Aug 12 – Sep 11 | — |
| Basil | Very tender | May 2 – May 16 | Jun 20 – Jun 27 | Jul 20 – Aug 4 | — |
| Lettuce | Half-hardy | May 2 – May 16 | May 16 – May 30 | Jun 30 – Jul 15 | Jun 23 – Jul 8 |
| Pea | Hardy | — | May 2 – May 16 | Jun 26 – Jul 11 | Jun 13 – Jun 28 |
| Spinach | Hardy | — | May 2 – May 16 | Jun 11 – Jun 21 | Jul 3 – Jul 13 |
| Carrot | Half-hardy | — | May 23 – May 30 | Jul 22 – Aug 11 | Jun 3 – Jun 23 |
| Broccoli | Half-hardy | Apr 18 – May 2 | May 16 – May 30 | Jul 10 – Jul 30 | Jun 8 – Jun 28 |
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 USW00024135. 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 | — | — | — | — | 49 |
| 32°F (freeze) | Jun 13 | Jul 1 | Sep 5 | Sep 19 | 83 |
| 28°F | May 21 | Jun 10 | Sep 17 | Oct 1 | 117 |
| 24°F | May 7 | May 19 | Oct 1 | Oct 15 | 146 |
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) | 1,210 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 2,742 | cool-season crops (brassicas, greens) |
Hardiness zone 5a
Butte-Silver Bow sits in USDA plant hardiness zone 5a on the 2023 map — meaning its average annual extreme minimum winter temperature is about −20 to −15 °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 5a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Butte-Silver Bow?
- Butte-Silver Bow, Montana is in USDA plant hardiness zone 5a on the 2023 map (average annual extreme minimum temperature −20 to −15 °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 Butte-Silver Bow?
- The average (median) last spring frost at 32°F is around June 13, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as July 1, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Butte-Silver Bow?
- The average first fall frost at 32°F is around September 5. That leaves a growing season of about 83 days between the average last spring and first fall frosts.
- When should I start tomatoes in Butte-Silver Bow?
- Start tomato seeds indoors about Apr 18 – May 2 and transplant them outside about Jun 20 – Jun 27, once the danger of frost has passed. Estimated first harvest is around Aug 19 – Sep 8.
- How long is the growing season in Butte-Silver Bow?
- About 83 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~June 13) and the average first fall frost (~September 5). 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 USW00024135 (Butte Bert Mooney Ap, 8.1 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.