Belle Plaine, IA planting calendar
- USDA zone
- 5a−20 to −15 °F
- Last frost
- Apr 28avg, 32°F
- First frost
- Oct 10avg, 32°F
- Growing season
- 165days
Belle Plaine, Iowa is in USDA plant hardiness zone 5a. Its average last spring frost is around April 28 and the first fall frost around October 10, giving a growing season of about 165 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.
Belle Plaine planting calendar
Each crop's windows are counted from Belle Plaine'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 3 – Mar 17 | May 5 – May 12 | Jul 4 – Jul 24 | — |
| Pepper | Very tender | Feb 17 – Mar 3 | May 12 – May 19 | Jul 11 – Aug 10 | — |
| Cucumber | Tender | Mar 31 – Apr 7 | May 5 – May 12 | Jun 24 – Jul 14 | — |
| Summer squash / zucchini | Tender | — | May 5 – May 12 | Jun 19 – Jul 4 | — |
| Bush bean | Tender | — | May 5 – May 12 | Jun 24 – Jul 4 | Aug 11 – Aug 21 |
| Sweet corn | Tender | — | Apr 28 – May 12 | Jun 27 – Jul 27 | — |
| Basil | Very tender | Mar 17 – Mar 31 | May 5 – May 12 | Jun 4 – Jun 19 | — |
| Lettuce | Half-hardy | Mar 17 – Mar 31 | Mar 31 – Apr 14 | May 15 – May 30 | Jul 28 – Aug 12 |
| Pea | Hardy | — | Mar 17 – Mar 31 | May 11 – May 26 | Jul 18 – Aug 2 |
| Spinach | Hardy | — | Mar 17 – Mar 31 | Apr 26 – May 6 | Aug 7 – Aug 17 |
| Carrot | Half-hardy | — | Apr 7 – Apr 14 | Jun 6 – Jun 26 | Jul 8 – Jul 28 |
| Broccoli | Half-hardy | Mar 3 – Mar 17 | Mar 31 – Apr 14 | May 25 – Jun 14 | Jul 13 – Aug 2 |
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 USC00130600. 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 6 | May 20 | Oct 1 | Oct 13 | 147 |
| 32°F (freeze) | Apr 28 | May 11 | Oct 10 | Oct 23 | 165 |
| 28°F | Apr 16 | May 2 | Oct 21 | Nov 1 | 185 |
| 24°F | Apr 5 | Apr 23 | Oct 30 | Nov 12 | 207 |
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) | 2,989 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 5,065 | cool-season crops (brassicas, greens) |
Hardiness zone 5a
Belle Plaine 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 Belle Plaine?
- Belle Plaine, Iowa 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 Belle Plaine?
- The average (median) last spring frost at 32°F is around April 28, 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 11, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Belle Plaine?
- The average first fall frost at 32°F is around October 10. That leaves a growing season of about 165 days between the average last spring and first fall frosts.
- When should I start tomatoes in Belle Plaine?
- Start tomato seeds indoors about Mar 3 – Mar 17 and transplant them outside about May 5 – May 12, once the danger of frost has passed. Estimated first harvest is around Jul 4 – Jul 24.
- How long is the growing season in Belle Plaine?
- About 165 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~April 28) and the average first fall frost (~October 10). 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 USC00130600 (Belle Plaine, 1.7 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.