Frost dates for 61327Hennepin, IL
The average last spring frost in Hennepin is April 24 and the average first fall frost is October 17, giving a typical growing season of about 174 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 24
- Average first fall frost
- Oct 17
- Growing season
- 174 days
Safer after May 10 (1-in-10 risk)
Possible by Oct 1 (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 22 · May 5 · May 20 | Sep 23 · Oct 7 · Oct 19 | 154 days | 100% |
| Frost / freeze (32°F) | Apr 11 · Apr 24 · May 10 | Oct 1 · Oct 17 · Oct 29 | 174 days | 100% |
| Hard freeze (28°F) | Apr 1 · Apr 13 · Apr 29 | Oct 14 · Oct 27 · Nov 9 | 196 days | 100% |
Planting calendar for Hennepin
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 24 – May 30 |
| Tomatoes | Transplant outdoors | May 10 – Jun 27 |
| Peppers | Start seeds indoors | Mar 24 – Apr 24 |
| Peppers | Transplant outdoors | May 24 – Jun 24 |
| Eggplant | Start seeds indoors | Apr 10 – May 9 |
| Eggplant | Transplant outdoors | May 24 – Jun 24 |
| Cucumbers | Sow outdoors | May 24 – Jul 7 |
| Summer squash | Sow outdoors | May 10 – Jun 24 |
| Winter squash & pumpkins | Sow outdoors | May 24 – Jun 24 |
| Snap beans | Sow outdoors | May 10 – Jul 30 |
| Sweet corn | Sow outdoors | May 10 – Jun 27 |
| Watermelon & cantaloupe | Sow outdoors | May 24 – Jun 24 |
| Okra | Sow outdoors | May 17 – Jun 9 |
| Peas | Sow outdoors (spring) | Mar 24 – May 9 |
| Potatoes | Plant outdoors (spring) | Mar 24 – May 24 |
| Onions | Start seeds indoors (spring) | Feb 10 – Mar 9 |
| Onions | Transplant outdoors (spring) | Apr 10 – May 9 |
| Broccoli | Start seeds indoors (spring) | Mar 6 – Apr 9 |
| Broccoli | Transplant outdoors (spring) | Apr 10 – May 9 |
| Broccoli | Start seeds indoors (fall) | Jun 17 – Jun 27 |
| Broccoli | Transplant outdoors (fall) | Jul 17 – Jul 28 |
| Cabbage | Start seeds indoors (spring) | Feb 24 – Mar 24 |
| Cabbage | Transplant outdoors (spring) | Mar 24 – Apr 24 |
| Cabbage | Start seeds indoors (fall) | Jun 7 – Jul 7 |
| Cabbage | Transplant outdoors (fall) | Jul 7 – Aug 7 |
| Leaf lettuce | Sow outdoors (spring) | Mar 24 – Jun 9 |
| Leaf lettuce | Sow outdoors (fall) | Jul 7 – Aug 23 |
| Spinach | Sow outdoors (spring) | Mar 17 – Apr 30 |
| Spinach | Sow outdoors (fall) | Jul 24 – Aug 28 |
| Radishes | Sow outdoors (spring) | Mar 24 – May 14 |
| Radishes | Sow outdoors (fall) | Jul 7 – Sep 7 |
| Kale | Sow outdoors (spring) | Apr 10 – Apr 30 |
| Kale | Sow outdoors (fall) | Jun 30 – Aug 7 |
| Carrots | Sow outdoors (spring) | Apr 24 – Jun 9 |
| Carrots | Sow outdoors (fall) | Jun 7 – Jul 23 |
| Garlic | Plant outdoors (fall) | Oct 7 – Nov 7 |
Where these dates come from
ZIP code 61327 is matched to the NOAA station Hennepin Wtr Trmt Plt, IL, 3.6 km away, at 460 ft elevation (65 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Hennepin Wtr Trmt Plt, IL (used) | 460 ft | Apr 24 | Oct 17 |
| Hennepin, IL | 515 ft | Apr 18 | Oct 22 |
| Princeton, IL | 697 ft | Apr 22 | Oct 17 |
| Peru, IL | 620 ft | Apr 24 | Oct 18 |
Frost dates near Hennepin
- Mark, IL 61340 · last Apr 24, first Oct 17
- Bureau, IL 61315 · last Apr 24, first Oct 17
- Depue, IL 61322 · last Apr 24, first Oct 17
- Granville, IL 61326 · last Apr 24, first Oct 18
- Putnam, IL 61560 · last Apr 24, first Oct 17
- Mc Nabb, IL 61335 · last Apr 24, first Oct 17
- Standard, IL 61363 · last Apr 24, first Oct 18
- Spring Valley, IL 61362 · last Apr 24, first Oct 18
Frequently asked questions
- When is the last frost in Hennepin, IL?
- For ZIP code 61327, the average last spring frost (32°F) is April 24, based on NOAA 1991-2020 climate normals for the Hennepin Wtr Trmt Plt, IL weather station. There is a 1-in-10 chance of a frost after May 10.
- When is the first frost in Hennepin, IL?
- The average first fall frost (32°F) is October 17. 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 61327?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 174 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.