Frost dates for 50459Northwood, IA
The average last spring frost in Northwood is May 4 and the average first fall frost is October 4, giving a typical growing season of about 152 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 4
- Average first fall frost
- Oct 4
- Growing season
- 152 days
Safer after May 16 (1-in-10 risk)
Possible by Sep 20 (1-in-10 risk)
Last frost typically in 189 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) | May 1 · May 13 · May 27 | Sep 13 · Sep 25 · Oct 7 | 133 days | 100% |
| Frost / freeze (32°F) | Apr 21 · May 4 · May 16 | Sep 20 · Oct 4 · Oct 17 | 152 days | 100% |
| Hard freeze (28°F) | Apr 9 · Apr 24 · May 7 | Oct 1 · Oct 13 · Oct 25 | 172 days | 100% |
Planting calendar for Northwood
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 | Apr 3 – Jun 9 |
| Tomatoes | Transplant outdoors | May 20 – Jun 14 |
| Peppers | Start seeds indoors | Apr 3 – May 4 |
| Peppers | Transplant outdoors | Jun 3 – Jul 4 |
| Eggplant | Start seeds indoors | Apr 20 – May 19 |
| Eggplant | Transplant outdoors | Jun 3 – Jul 4 |
| Cucumbers | Sow outdoors | Jun 3 – Jun 24 |
| Summer squash | Sow outdoors | May 20 – Jul 4 |
| Winter squash & pumpkins | Sow outdoors | Jun 3 – Jul 4 |
| Snap beans | Sow outdoors | May 20 – Jul 17 |
| Sweet corn | Sow outdoors | May 20 – Jun 14 |
| Watermelon & cantaloupe | Sow outdoors | Jun 3 – Jul 4 |
| Okra | Sow outdoors | May 27 – Jun 19 |
| Peas | Sow outdoors (spring) | Apr 3 – May 19 |
| Potatoes | Plant outdoors (spring) | Apr 3 – Jun 3 |
| Onions | Start seeds indoors (spring) | Feb 20 – Mar 19 |
| Onions | Transplant outdoors (spring) | Apr 20 – May 19 |
| Broccoli | Start seeds indoors (spring) | Mar 16 – Apr 19 |
| Broccoli | Transplant outdoors (spring) | Apr 20 – May 19 |
| Broccoli | Start seeds indoors (fall) | Jun 4 – Jun 14 |
| Broccoli | Transplant outdoors (fall) | Jul 4 – Jul 15 |
| Cabbage | Start seeds indoors (spring) | Mar 6 – Apr 3 |
| Cabbage | Transplant outdoors (spring) | Apr 3 – May 4 |
| Cabbage | Start seeds indoors (fall) | May 25 – Jun 24 |
| Cabbage | Transplant outdoors (fall) | Jun 24 – Jul 25 |
| Leaf lettuce | Sow outdoors (spring) | Apr 3 – Jun 19 |
| Leaf lettuce | Sow outdoors (fall) | Jun 24 – Aug 10 |
| Spinach | Sow outdoors (spring) | Mar 27 – May 10 |
| Spinach | Sow outdoors (fall) | Jul 11 – Aug 15 |
| Radishes | Sow outdoors (spring) | Apr 3 – May 24 |
| Radishes | Sow outdoors (fall) | Jun 24 – Aug 25 |
| Kale | Sow outdoors (spring) | Apr 20 – May 10 |
| Kale | Sow outdoors (fall) | Jun 17 – Jul 25 |
| Carrots | Sow outdoors (spring) | May 4 – Jun 19 |
| Carrots | Sow outdoors (fall) | May 25 – Jul 10 |
| Garlic | Plant outdoors (fall) | Sep 24 – Oct 25 |
Where these dates come from
ZIP code 50459 is matched to the NOAA station Northwood, IA, 1.9 km away, at 1,190 ft elevation (17 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Northwood, IA (used) | 1,190 ft | May 4 | Oct 4 |
| Albert Lea 3Se, MN | 1,230 ft | Apr 27 | Oct 9 |
| Austin Waste Wtp Facility, MN | 1,199 ft | Apr 30 | Oct 5 |
| Mason City, IA | 1,105 ft | Apr 29 | Oct 7 |
Frost dates near Northwood
- Kensett, IA 50448 · last May 4, first Oct 4
- Glenville, MN 56036 · last Apr 27, first Oct 9
- Manly, IA 50456 · last May 4, first Oct 4
- Joice, IA 50446 · last Apr 30, first Oct 7
- Carpenter, IA 50426 · last May 4, first Oct 4
- Twin Lakes, MN 56089 · last Apr 27, first Oct 9
- Grafton, IA 50440 · last May 4, first Oct 4
- Emmons, MN 56029 · last Apr 27, first Oct 9
Frequently asked questions
- When is the last frost in Northwood, IA?
- For ZIP code 50459, the average last spring frost (32°F) is May 4, based on NOAA 1991-2020 climate normals for the Northwood, IA weather station. There is a 1-in-10 chance of a frost after May 16.
- When is the first frost in Northwood, IA?
- The average first fall frost (32°F) is October 4. There is a 1-in-10 chance of frost by September 20, so tender plants are at risk from that point on.
- How long is the growing season in 50459?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 152 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.