Frost dates for 50116Hamilton, IA
The average last spring frost in Hamilton is April 20 and the average first fall frost is October 19, giving a typical growing season of about 180 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 20
- Average first fall frost
- Oct 19
- Growing season
- 180 days
Safer after May 4 (1-in-10 risk)
Possible by Oct 1 (1-in-10 risk)
Last frost typically in 169 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 15 · Apr 30 · May 12 | Sep 23 · Oct 7 · Oct 21 | 159 days | 100% |
| Frost / freeze (32°F) | Apr 6 · Apr 20 · May 4 | Oct 1 · Oct 19 · Nov 1 | 180 days | 100% |
| Hard freeze (28°F) | Mar 28 · Apr 10 · Apr 24 | Oct 14 · Oct 29 · Nov 9 | 199 days | 100% |
Planting calendar for Hamilton
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 20 – May 26 |
| Tomatoes | Transplant outdoors | May 6 – Jun 29 |
| Peppers | Start seeds indoors | Mar 20 – Apr 20 |
| Peppers | Transplant outdoors | May 20 – Jun 20 |
| Eggplant | Start seeds indoors | Apr 6 – May 5 |
| Eggplant | Transplant outdoors | May 20 – Jun 20 |
| Cucumbers | Sow outdoors | May 20 – Jul 9 |
| Summer squash | Sow outdoors | May 6 – Jun 20 |
| Winter squash & pumpkins | Sow outdoors | May 20 – Jun 20 |
| Snap beans | Sow outdoors | May 6 – Aug 1 |
| Sweet corn | Sow outdoors | May 6 – Jun 29 |
| Watermelon & cantaloupe | Sow outdoors | May 20 – Jun 20 |
| Okra | Sow outdoors | May 13 – Jun 5 |
| Peas | Sow outdoors (spring) | Mar 20 – May 5 |
| Potatoes | Plant outdoors (spring) | Mar 20 – May 20 |
| Onions | Start seeds indoors (spring) | Feb 6 – Mar 5 |
| Onions | Transplant outdoors (spring) | Apr 6 – May 5 |
| Broccoli | Start seeds indoors (spring) | Mar 2 – Apr 5 |
| Broccoli | Transplant outdoors (spring) | Apr 6 – May 5 |
| Broccoli | Start seeds indoors (fall) | Jun 19 – Jun 29 |
| Broccoli | Transplant outdoors (fall) | Jul 19 – Jul 30 |
| Cabbage | Start seeds indoors (spring) | Feb 20 – Mar 20 |
| Cabbage | Transplant outdoors (spring) | Mar 20 – Apr 20 |
| Cabbage | Start seeds indoors (fall) | Jun 9 – Jul 9 |
| Cabbage | Transplant outdoors (fall) | Jul 9 – Aug 9 |
| Leaf lettuce | Sow outdoors (spring) | Mar 20 – Jun 5 |
| Leaf lettuce | Sow outdoors (fall) | Jul 9 – Aug 25 |
| Spinach | Sow outdoors (spring) | Mar 13 – Apr 26 |
| Spinach | Sow outdoors (fall) | Jul 26 – Aug 30 |
| Radishes | Sow outdoors (spring) | Mar 20 – May 10 |
| Radishes | Sow outdoors (fall) | Jul 9 – Sep 9 |
| Kale | Sow outdoors (spring) | Apr 6 – Apr 26 |
| Kale | Sow outdoors (fall) | Jul 2 – Aug 9 |
| Carrots | Sow outdoors (spring) | Apr 20 – Jun 5 |
| Carrots | Sow outdoors (fall) | Jun 9 – Jul 25 |
| Garlic | Plant outdoors (fall) | Oct 9 – Nov 9 |
Where these dates come from
ZIP code 50116 is matched to the NOAA station Knoxville, IA, 19.1 km away, at 895 ft elevation (58 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Knoxville, IA (used) | 895 ft | Apr 20 | Oct 19 |
| Albia 3 Nne, IA | 880 ft | Apr 24 | Oct 16 |
| Oskaloosa, IA | 830 ft | Apr 21 | Oct 16 |
| Chariton 1 E, IA | 965 ft | May 5 | Oct 5 |
Frost dates near Hamilton
- Bussey, IA 50044 · last Apr 24, first Oct 16
- Lovilia, IA 50150 · last Apr 24, first Oct 16
- Tracy, IA 50256 · last Apr 21, first Oct 16
- Harvey, IA 50119 · last Apr 20, first Oct 19
- Columbia, IA 50057 · last Apr 20, first Oct 19
- Knoxville, IA 50138 · last Apr 20, first Oct 19
- Albia, IA 52531 · last Apr 24, first Oct 16
- Leighton, IA 50143 · last Apr 21, first Oct 16
Frequently asked questions
- When is the last frost in Hamilton, IA?
- For ZIP code 50116, the average last spring frost (32°F) is April 20, based on NOAA 1991-2020 climate normals for the Knoxville, IA weather station. There is a 1-in-10 chance of a frost after May 4.
- When is the first frost in Hamilton, IA?
- The average first fall frost (32°F) is October 19. There is a 1-in-10 chance of frost by October 1, so tender plants are at risk from that point on.
- How long is the growing season in 50116?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 180 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.