Frost dates for 51357Royal, IA
The average last spring frost in Royal is May 2 and the average first fall frost is October 2, giving a typical growing season of about 154 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 2
- Average first fall frost
- Oct 2
- Growing season
- 154 days
Safer after May 15 (1-in-10 risk)
Possible by Sep 18 (1-in-10 risk)
Last frost typically in 187 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 28 · May 9 · May 22 | Sep 9 · Sep 24 · Oct 7 | 136 days | 100% |
| Frost / freeze (32°F) | Apr 17 · May 2 · May 15 | Sep 18 · Oct 2 · Oct 16 | 154 days | 100% |
| Hard freeze (28°F) | Apr 8 · Apr 22 · May 7 | Sep 26 · Oct 12 · Oct 27 | 172 days | 100% |
Planting calendar for Royal
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 1 – Jun 7 |
| Tomatoes | Transplant outdoors | May 18 – Jun 12 |
| Peppers | Start seeds indoors | Apr 1 – May 2 |
| Peppers | Transplant outdoors | Jun 1 – Jul 2 |
| Eggplant | Start seeds indoors | Apr 18 – May 17 |
| Eggplant | Transplant outdoors | Jun 1 – Jul 2 |
| Cucumbers | Sow outdoors | Jun 1 – Jun 22 |
| Summer squash | Sow outdoors | May 18 – Jul 2 |
| Winter squash & pumpkins | Sow outdoors | Jun 1 – Jul 2 |
| Snap beans | Sow outdoors | May 18 – Jul 15 |
| Sweet corn | Sow outdoors | May 18 – Jun 12 |
| Watermelon & cantaloupe | Sow outdoors | Jun 1 – Jul 2 |
| Okra | Sow outdoors | May 25 – Jun 17 |
| Peas | Sow outdoors (spring) | Apr 1 – May 17 |
| Potatoes | Plant outdoors (spring) | Apr 1 – Jun 1 |
| Onions | Start seeds indoors (spring) | Feb 18 – Mar 17 |
| Onions | Transplant outdoors (spring) | Apr 18 – May 17 |
| Broccoli | Start seeds indoors (spring) | Mar 14 – Apr 17 |
| Broccoli | Transplant outdoors (spring) | Apr 18 – May 17 |
| Broccoli | Start seeds indoors (fall) | Jun 2 – Jun 12 |
| Broccoli | Transplant outdoors (fall) | Jul 2 – Jul 13 |
| Cabbage | Start seeds indoors (spring) | Mar 4 – Apr 1 |
| Cabbage | Transplant outdoors (spring) | Apr 1 – May 2 |
| Cabbage | Start seeds indoors (fall) | May 23 – Jun 22 |
| Cabbage | Transplant outdoors (fall) | Jun 22 – Jul 23 |
| Leaf lettuce | Sow outdoors (spring) | Apr 1 – Jun 17 |
| Leaf lettuce | Sow outdoors (fall) | Jun 22 – Aug 8 |
| Spinach | Sow outdoors (spring) | Mar 25 – May 8 |
| Spinach | Sow outdoors (fall) | Jul 9 – Aug 13 |
| Radishes | Sow outdoors (spring) | Apr 1 – May 22 |
| Radishes | Sow outdoors (fall) | Jun 22 – Aug 23 |
| Kale | Sow outdoors (spring) | Apr 18 – May 8 |
| Kale | Sow outdoors (fall) | Jun 15 – Jul 23 |
| Carrots | Sow outdoors (spring) | May 2 – Jun 17 |
| Carrots | Sow outdoors (fall) | May 23 – Jul 8 |
| Garlic | Plant outdoors (fall) | Sep 22 – Oct 23 |
Where these dates come from
ZIP code 51357 is matched to the NOAA station Spencer Muni Ap, IA, 13.9 km away, at 1,338 ft elevation (73 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Spencer Muni Ap, IA (used) | 1,338 ft | May 2 | Oct 2 |
| Spencer 1 N, IA | 1,326 ft | May 1 | Oct 3 |
| Sioux Rapids 4 E, IA | 1,420 ft | Apr 30 | Oct 5 |
| Primghar, IA | 1,520 ft | Apr 29 | Oct 10 |
Frost dates near Royal
- Fostoria, IA 51340 · last May 1, first Oct 3
- Everly, IA 51338 · last May 2, first Oct 2
- Peterson, IA 51047 · last Apr 30, first Oct 5
- Spencer, IA 51301 · last May 1, first Oct 3
- Greenville, IA 51343 · last Apr 30, first Oct 5
- Gillett Grove, IA 51341 · last Apr 30, first Oct 5
- Sutherland, IA 51058 · last Apr 29, first Oct 10
- Sioux Rapids, IA 50585 · last Apr 30, first Oct 5
Frequently asked questions
- When is the last frost in Royal, IA?
- For ZIP code 51357, the average last spring frost (32°F) is May 2, based on NOAA 1991-2020 climate normals for the Spencer Muni Ap, IA weather station. There is a 1-in-10 chance of a frost after May 15.
- When is the first frost in Royal, IA?
- The average first fall frost (32°F) is October 2. There is a 1-in-10 chance of frost by September 18, so tender plants are at risk from that point on.
- How long is the growing season in 51357?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 154 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.