Frost dates for 52140Dorchester, IA
The average last spring frost in Dorchester is April 22 and the average first fall frost is October 17, giving a typical growing season of about 178 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 22
- Average first fall frost
- Oct 17
- Growing season
- 178 days
Safer after May 5 (1-in-10 risk)
Possible by Oct 4 (1-in-10 risk)
Last frost typically in 177 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 19 · May 2 · May 15 | Sep 23 · Oct 7 · Oct 21 | 157 days | 100% |
| Frost / freeze (32°F) | Apr 6 · Apr 22 · May 5 | Oct 4 · Oct 17 · Oct 31 | 178 days | 100% |
| Hard freeze (28°F) | Mar 29 · Apr 10 · Apr 24 | Oct 13 · Oct 28 · Nov 9 | 200 days | 100% |
Planting calendar for Dorchester
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 22 – May 28 |
| Tomatoes | Transplant outdoors | May 8 – Jun 27 |
| Peppers | Start seeds indoors | Mar 22 – Apr 22 |
| Peppers | Transplant outdoors | May 22 – Jun 22 |
| Eggplant | Start seeds indoors | Apr 8 – May 7 |
| Eggplant | Transplant outdoors | May 22 – Jun 22 |
| Cucumbers | Sow outdoors | May 22 – Jul 7 |
| Summer squash | Sow outdoors | May 8 – Jun 22 |
| Winter squash & pumpkins | Sow outdoors | May 22 – Jun 22 |
| Snap beans | Sow outdoors | May 8 – Jul 30 |
| Sweet corn | Sow outdoors | May 8 – Jun 27 |
| Watermelon & cantaloupe | Sow outdoors | May 22 – Jun 22 |
| Okra | Sow outdoors | May 15 – Jun 7 |
| Peas | Sow outdoors (spring) | Mar 22 – May 7 |
| Potatoes | Plant outdoors (spring) | Mar 22 – May 22 |
| Onions | Start seeds indoors (spring) | Feb 8 – Mar 7 |
| Onions | Transplant outdoors (spring) | Apr 8 – May 7 |
| Broccoli | Start seeds indoors (spring) | Mar 4 – Apr 7 |
| Broccoli | Transplant outdoors (spring) | Apr 8 – May 7 |
| Broccoli | Start seeds indoors (fall) | Jun 17 – Jun 27 |
| Broccoli | Transplant outdoors (fall) | Jul 17 – Jul 28 |
| Cabbage | Start seeds indoors (spring) | Feb 22 – Mar 22 |
| Cabbage | Transplant outdoors (spring) | Mar 22 – Apr 22 |
| Cabbage | Start seeds indoors (fall) | Jun 7 – Jul 7 |
| Cabbage | Transplant outdoors (fall) | Jul 7 – Aug 7 |
| Leaf lettuce | Sow outdoors (spring) | Mar 22 – Jun 7 |
| Leaf lettuce | Sow outdoors (fall) | Jul 7 – Aug 23 |
| Spinach | Sow outdoors (spring) | Mar 15 – Apr 28 |
| Spinach | Sow outdoors (fall) | Jul 24 – Aug 28 |
| Radishes | Sow outdoors (spring) | Mar 22 – May 12 |
| Radishes | Sow outdoors (fall) | Jul 7 – Sep 7 |
| Kale | Sow outdoors (spring) | Apr 8 – Apr 28 |
| Kale | Sow outdoors (fall) | Jun 30 – Aug 7 |
| Carrots | Sow outdoors (spring) | Apr 22 – Jun 7 |
| Carrots | Sow outdoors (fall) | Jun 7 – Jul 23 |
| Garlic | Plant outdoors (fall) | Oct 7 – Nov 7 |
Where these dates come from
ZIP code 52140 is matched to the NOAA station Genoa Dam 8, WI, 26.6 km away, at 639 ft elevation (73 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Genoa Dam 8, WI (used) | 639 ft | Apr 22 | Oct 17 |
| Waukon, IA | 1,275 ft | May 2 | Oct 11 |
| Caledonia, MN | 1,166 ft | Apr 29 | Oct 10 |
| Mabel, MN | 1,112 ft | May 10 | Sep 28 |
Frost dates near Dorchester
- Eitzen, MN 55931 · last Apr 29, first Oct 10
- Highlandville, IA 52149 · last Apr 29, first Oct 10
- Spring Grove, MN 55974 · last Apr 29, first Oct 10
- New Albin, IA 52160 · last Apr 22, first Oct 17
- Waukon, IA 52172 · last May 2, first Oct 11
- Caledonia, MN 55921 · last Apr 29, first Oct 10
- Lansing, IA 52151 · last Apr 24, first Oct 17
- Mabel, MN 55954 · last May 10, first Sep 28
Frequently asked questions
- When is the last frost in Dorchester, IA?
- For ZIP code 52140, the average last spring frost (32°F) is April 22, based on NOAA 1991-2020 climate normals for the Genoa Dam 8, WI weather station. There is a 1-in-10 chance of a frost after May 5.
- When is the first frost in Dorchester, IA?
- The average first fall frost (32°F) is October 17. There is a 1-in-10 chance of frost by October 4, so tender plants are at risk from that point on.
- How long is the growing season in 52140?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 178 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.