Marvel, CO planting calendar
- USDA zone
- 6a−10 to −5 °F
- Last frost
- Jun 1avg, 32°F
- First frost
- Sep 27avg, 32°F
- Growing season
- 116days
Marvel, Colorado is in USDA plant hardiness zone 6a. Its average last spring frost is around June 1 and the first fall frost around September 27, giving a growing season of about 116 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.
Marvel planting calendar
Each crop's windows are counted from Marvel'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 6 – Apr 20 | Jun 8 – Jun 15 | Aug 7 – Aug 27 | — |
| Pepper | Very tender | Mar 23 – Apr 6 | Jun 15 – Jun 22 | Aug 14 – Sep 13 | — |
| Cucumber | Tender | May 4 – May 11 | Jun 8 – Jun 15 | Jul 28 – Aug 17 | — |
| Summer squash / zucchini | Tender | — | Jun 8 – Jun 15 | Jul 23 – Aug 7 | — |
| Bush bean | Tender | — | Jun 8 – Jun 15 | Jul 28 – Aug 7 | Jul 29 – Aug 8 |
| Sweet corn | Tender | — | Jun 1 – Jun 15 | Jul 31 – Aug 30 | — |
| Basil | Very tender | Apr 20 – May 4 | Jun 8 – Jun 15 | Jul 8 – Jul 23 | — |
| Lettuce | Half-hardy | Apr 20 – May 4 | May 4 – May 18 | Jun 18 – Jul 3 | Jul 15 – Jul 30 |
| Pea | Hardy | — | Apr 20 – May 4 | Jun 14 – Jun 29 | Jul 5 – Jul 20 |
| Spinach | Hardy | — | Apr 20 – May 4 | May 30 – Jun 9 | Jul 25 – Aug 4 |
| Carrot | Half-hardy | — | May 11 – May 18 | Jul 10 – Jul 30 | Jun 25 – Jul 15 |
| Broccoli | Half-hardy | Apr 6 – Apr 20 | May 4 – May 18 | Jun 28 – Jul 18 | 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 USC00053016. 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 15 | Jul 1 | Sep 19 | Sep 29 | 93 |
| 32°F (freeze) | Jun 1 | Jun 19 | Sep 27 | Oct 8 | 116 |
| 28°F | May 17 | Jun 8 | Oct 6 | Oct 20 | 139 |
| 24°F | Apr 30 | May 19 | Oct 15 | Oct 31 | 165 |
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) | 1,577 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,376 | cool-season crops (brassicas, greens) |
Hardiness zone 6a
Marvel sits in USDA plant hardiness zone 6a on the 2023 map — meaning its average annual extreme minimum winter temperature is about −10 to −5 °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 6a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Marvel?
- Marvel, Colorado is in USDA plant hardiness zone 6a on the 2023 map (average annual extreme minimum temperature −10 to −5 °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 Marvel?
- The average (median) last spring frost at 32°F is around June 1, 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 19, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Marvel?
- The average first fall frost at 32°F is around September 27. That leaves a growing season of about 116 days between the average last spring and first fall frosts.
- When should I start tomatoes in Marvel?
- Start tomato seeds indoors about Apr 6 – Apr 20 and transplant them outside about Jun 8 – Jun 15, once the danger of frost has passed. Estimated first harvest is around Aug 7 – Aug 27.
- How long is the growing season in Marvel?
- About 116 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~June 1) 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 USC00053016 (Ft Lewis, 11.1 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.