Frost dates for 50129Jefferson, IA
The average last spring frost in Jefferson is April 26 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 26
- Average first fall frost
- Oct 9
- Growing season
- 164 days
Safer after May 8 (1-in-10 risk)
Possible by Sep 23 (1-in-10 risk)
Last frost typically in 175 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 22 · May 4 · May 17 | Sep 16 · Sep 29 · Oct 13 | 147 days | 100% |
| Frost / freeze (32°F) | Apr 12 · Apr 26 · May 8 | Sep 23 · Oct 9 · Oct 24 | 164 days | 100% |
| Hard freeze (28°F) | Apr 1 · Apr 15 · Apr 29 | Oct 3 · Oct 21 · Nov 2 | 185 days | 100% |
Planting calendar for Jefferson
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 26 – Jun 1 |
| Tomatoes | Transplant outdoors | May 12 – Jun 19 |
| Peppers | Start seeds indoors | Mar 26 – Apr 26 |
| Peppers | Transplant outdoors | May 26 – Jun 26 |
| Eggplant | Start seeds indoors | Apr 12 – May 11 |
| Eggplant | Transplant outdoors | May 26 – Jun 26 |
| Cucumbers | Sow outdoors | May 26 – Jun 29 |
| Summer squash | Sow outdoors | May 12 – Jun 26 |
| Winter squash & pumpkins | Sow outdoors | May 26 – Jun 26 |
| Snap beans | Sow outdoors | May 12 – Jul 22 |
| Sweet corn | Sow outdoors | May 12 – Jun 19 |
| Watermelon & cantaloupe | Sow outdoors | May 26 – Jun 26 |
| Okra | Sow outdoors | May 19 – Jun 11 |
| Peas | Sow outdoors (spring) | Mar 26 – May 11 |
| Potatoes | Plant outdoors (spring) | Mar 26 – May 26 |
| Onions | Start seeds indoors (spring) | Feb 12 – Mar 11 |
| Onions | Transplant outdoors (spring) | Apr 12 – May 11 |
| Broccoli | Start seeds indoors (spring) | Mar 8 – Apr 11 |
| Broccoli | Transplant outdoors (spring) | Apr 12 – May 11 |
| Broccoli | Start seeds indoors (fall) | Jun 9 – Jun 19 |
| Broccoli | Transplant outdoors (fall) | Jul 9 – Jul 20 |
| Cabbage | Start seeds indoors (spring) | Feb 26 – Mar 26 |
| Cabbage | Transplant outdoors (spring) | Mar 26 – Apr 26 |
| Cabbage | Start seeds indoors (fall) | May 30 – Jun 29 |
| Cabbage | Transplant outdoors (fall) | Jun 29 – Jul 30 |
| Leaf lettuce | Sow outdoors (spring) | Mar 26 – Jun 11 |
| Leaf lettuce | Sow outdoors (fall) | Jun 29 – Aug 15 |
| Spinach | Sow outdoors (spring) | Mar 19 – May 2 |
| Spinach | Sow outdoors (fall) | Jul 16 – Aug 20 |
| Radishes | Sow outdoors (spring) | Mar 26 – May 16 |
| Radishes | Sow outdoors (fall) | Jun 29 – Aug 30 |
| Kale | Sow outdoors (spring) | Apr 12 – May 2 |
| Kale | Sow outdoors (fall) | Jun 22 – Jul 30 |
| Carrots | Sow outdoors (spring) | Apr 26 – Jun 11 |
| Carrots | Sow outdoors (fall) | May 30 – Jul 15 |
| Garlic | Plant outdoors (fall) | Sep 29 – Oct 30 |
Where these dates come from
ZIP code 50129 is matched to the NOAA station Jefferson, IA, 0.5 km away, at 1,055 ft elevation (68 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Jefferson, IA (used) | 1,055 ft | Apr 26 | Oct 9 |
| Perry, IA | 950 ft | Apr 25 | Oct 10 |
| Carroll, IA | 1,240 ft | Apr 27 | Oct 10 |
| Guthrie Ctr, IA | 1,065 ft | May 2 | Oct 3 |
Frost dates near Jefferson
- Cooper, IA 50059 · last Apr 26, first Oct 9
- Grand Junction, IA 50107 · last Apr 26, first Oct 9
- Scranton, IA 51462 · last Apr 26, first Oct 9
- Dana, IA 50064 · last Apr 26, first Oct 9
- Rippey, IA 50235 · last Apr 25, first Oct 10
- Churdan, IA 50050 · last Apr 26, first Oct 9
- Jamaica, IA 50128 · last Apr 26, first Oct 9
- Paton, IA 50217 · last Apr 26, first Oct 9
Frequently asked questions
- When is the last frost in Jefferson, IA?
- For ZIP code 50129, the average last spring frost (32°F) is April 26, based on NOAA 1991-2020 climate normals for the Jefferson, IA weather station. There is a 1-in-10 chance of a frost after May 8.
- When is the first frost in Jefferson, IA?
- The average first fall frost (32°F) is October 9. There is a 1-in-10 chance of frost by September 23, so tender plants are at risk from that point on.
- How long is the growing season in 50129?
- 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.