Frost dates for 52301Marengo, IA
The average last spring frost in Marengo is April 28 and the average first fall frost is October 9, giving a typical growing season of about 164 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 28
- Average first fall frost
- Oct 9
- Growing season
- 164 days
Safer after May 12 (1-in-10 risk)
Possible by Sep 24 (1-in-10 risk)
Last frost typically in 176 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 24 · May 7 · May 21 | Sep 17 · Sep 30 · Oct 11 | 145 days | 100% |
| Frost / freeze (32°F) | Apr 14 · Apr 28 · May 12 | Sep 24 · Oct 9 · Oct 21 | 164 days | 100% |
| Hard freeze (28°F) | Apr 4 · Apr 18 · May 2 | Oct 4 · Oct 19 · Oct 31 | 182 days | 100% |
Planting calendar for Marengo
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 28 – Jun 3 |
| Tomatoes | Transplant outdoors | May 14 – Jun 19 |
| Peppers | Start seeds indoors | Mar 28 – Apr 28 |
| Peppers | Transplant outdoors | May 28 – Jun 28 |
| Eggplant | Start seeds indoors | Apr 14 – May 13 |
| Eggplant | Transplant outdoors | May 28 – Jun 28 |
| Cucumbers | Sow outdoors | May 28 – Jun 29 |
| Summer squash | Sow outdoors | May 14 – Jun 28 |
| Winter squash & pumpkins | Sow outdoors | May 28 – Jun 28 |
| Snap beans | Sow outdoors | May 14 – Jul 22 |
| Sweet corn | Sow outdoors | May 14 – Jun 19 |
| Watermelon & cantaloupe | Sow outdoors | May 28 – Jun 28 |
| Okra | Sow outdoors | May 21 – Jun 13 |
| Peas | Sow outdoors (spring) | Mar 28 – May 13 |
| Potatoes | Plant outdoors (spring) | Mar 28 – May 28 |
| Onions | Start seeds indoors (spring) | Feb 14 – Mar 13 |
| Onions | Transplant outdoors (spring) | Apr 14 – May 13 |
| Broccoli | Start seeds indoors (spring) | Mar 10 – Apr 13 |
| Broccoli | Transplant outdoors (spring) | Apr 14 – May 13 |
| Broccoli | Start seeds indoors (fall) | Jun 9 – Jun 19 |
| Broccoli | Transplant outdoors (fall) | Jul 9 – Jul 20 |
| Cabbage | Start seeds indoors (spring) | Feb 28 – Mar 28 |
| Cabbage | Transplant outdoors (spring) | Mar 28 – Apr 28 |
| Cabbage | Start seeds indoors (fall) | May 30 – Jun 29 |
| Cabbage | Transplant outdoors (fall) | Jun 29 – Jul 30 |
| Leaf lettuce | Sow outdoors (spring) | Mar 28 – Jun 13 |
| Leaf lettuce | Sow outdoors (fall) | Jun 29 – Aug 15 |
| Spinach | Sow outdoors (spring) | Mar 21 – May 4 |
| Spinach | Sow outdoors (fall) | Jul 16 – Aug 20 |
| Radishes | Sow outdoors (spring) | Mar 28 – May 18 |
| Radishes | Sow outdoors (fall) | Jun 29 – Aug 30 |
| Kale | Sow outdoors (spring) | Apr 14 – May 4 |
| Kale | Sow outdoors (fall) | Jun 22 – Jul 30 |
| Carrots | Sow outdoors (spring) | Apr 28 – Jun 13 |
| Carrots | Sow outdoors (fall) | May 30 – Jul 15 |
| Garlic | Plant outdoors (fall) | Sep 29 – Oct 30 |
Where these dates come from
ZIP code 52301 is matched to the NOAA station Williamsburg 1E, IA, 14.8 km away, at 780 ft elevation (29 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Williamsburg 1E, IA (used) | 780 ft | Apr 28 | Oct 9 |
| Belle Plaine, IA | 810 ft | Apr 28 | Oct 10 |
| Cedar Rapids Muni Ap, IA | 868 ft | Apr 27 | Oct 11 |
| Vinton, IA | 850 ft | May 3 | Oct 3 |
Frost dates near Marengo
- Conroy, IA 52220 · last Apr 28, first Oct 9
- Ladora, IA 52251 · last Apr 28, first Oct 10
- South Amana, IA 52334 · last Apr 28, first Oct 9
- Blairstown, IA 52209 · last Apr 28, first Oct 10
- Middle Amana, IA 52307 · last Apr 28, first Oct 9
- Watkins, IA 52354 · last Apr 27, first Oct 11
- Luzerne, IA 52257 · last Apr 28, first Oct 10
- Amana, IA 52203 · last Apr 27, first Oct 11
Frequently asked questions
- When is the last frost in Marengo, IA?
- For ZIP code 52301, the average last spring frost (32°F) is April 28, based on NOAA 1991-2020 climate normals for the Williamsburg 1E, IA weather station. There is a 1-in-10 chance of a frost after May 12.
- When is the first frost in Marengo, IA?
- The average first fall frost (32°F) is October 9. There is a 1-in-10 chance of frost by September 24, so tender plants are at risk from that point on.
- How long is the growing season in 52301?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 164 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.