Frost dates for 63473Williamstown, MO
The average last spring frost in Williamstown is April 17 and the average first fall frost is October 19, giving a typical growing season of about 184 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 17
- Average first fall frost
- Oct 19
- Growing season
- 184 days
Safer after May 4 (1-in-10 risk)
Possible by Sep 30 (1-in-10 risk)
Last frost typically in 168 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 13 | Sep 20 · Oct 7 · Oct 22 | 160 days | 100% |
| Frost / freeze (32°F) | Apr 3 · Apr 17 · May 4 | Sep 30 · Oct 19 · Oct 31 | 184 days | 100% |
| Hard freeze (28°F) | Mar 22 · Apr 7 · Apr 23 | Oct 14 · Oct 30 · Nov 12 | 205 days | 100% |
Planting calendar for Williamstown
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 17 – May 23 |
| Tomatoes | Transplant outdoors | May 3 – Jun 29 |
| Peppers | Start seeds indoors | Mar 17 – Apr 17 |
| Peppers | Transplant outdoors | May 17 – Jun 17 |
| Eggplant | Start seeds indoors | Apr 3 – May 2 |
| Eggplant | Transplant outdoors | May 17 – Jun 17 |
| Cucumbers | Sow outdoors | May 17 – Jul 9 |
| Summer squash | Sow outdoors | May 3 – Jun 17 |
| Winter squash & pumpkins | Sow outdoors | May 17 – Jun 17 |
| Snap beans | Sow outdoors | May 3 – Aug 1 |
| Sweet corn | Sow outdoors | May 3 – Jun 29 |
| Watermelon & cantaloupe | Sow outdoors | May 17 – Jun 17 |
| Okra | Sow outdoors | May 10 – Jun 2 |
| Peas | Sow outdoors (spring) | Mar 17 – May 2 |
| Potatoes | Plant outdoors (spring) | Mar 17 – May 17 |
| Onions | Start seeds indoors (spring) | Feb 3 – Mar 2 |
| Onions | Transplant outdoors (spring) | Apr 3 – May 2 |
| Broccoli | Start seeds indoors (spring) | Feb 27 – Apr 2 |
| Broccoli | Transplant outdoors (spring) | Apr 3 – May 2 |
| Broccoli | Start seeds indoors (fall) | Jun 19 – Jun 29 |
| Broccoli | Transplant outdoors (fall) | Jul 19 – Jul 30 |
| Cabbage | Start seeds indoors (spring) | Feb 17 – Mar 17 |
| Cabbage | Transplant outdoors (spring) | Mar 17 – Apr 17 |
| Cabbage | Start seeds indoors (fall) | Jun 9 – Jul 9 |
| Cabbage | Transplant outdoors (fall) | Jul 9 – Aug 9 |
| Leaf lettuce | Sow outdoors (spring) | Mar 17 – Jun 2 |
| Leaf lettuce | Sow outdoors (fall) | Jul 9 – Aug 25 |
| Spinach | Sow outdoors (spring) | Mar 10 – Apr 23 |
| Spinach | Sow outdoors (fall) | Jul 26 – Aug 30 |
| Radishes | Sow outdoors (spring) | Mar 17 – May 7 |
| Radishes | Sow outdoors (fall) | Jul 9 – Sep 9 |
| Kale | Sow outdoors (spring) | Apr 3 – Apr 23 |
| Kale | Sow outdoors (fall) | Jul 2 – Aug 9 |
| Carrots | Sow outdoors (spring) | Apr 17 – Jun 2 |
| Carrots | Sow outdoors (fall) | Jun 9 – Jul 25 |
| Garlic | Plant outdoors (fall) | Oct 9 – Nov 9 |
Where these dates come from
ZIP code 63473 is matched to the NOAA station Steffenville, MO, 32.2 km away, at 705 ft elevation (7 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Steffenville, MO (used) | 705 ft | Apr 17 | Oct 19 |
| Canton L&D 20, MO | 490 ft | Apr 11 | Oct 23 |
| Keokuk Lock Dam 19, IA | 527 ft | Apr 10 | Oct 27 |
| Memphis, MO | 770 ft | Apr 23 | Oct 17 |
Frost dates near Williamstown
- Monticello, MO 63457 · last Apr 11, first Oct 23
- Wyaconda, MO 63474 · last Apr 23, first Oct 17
- Lewistown, MO 63452 · last Apr 17, first Oct 19
- La Belle, MO 63447 · last Apr 17, first Oct 19
- Kahoka, MO 63445 · last Apr 17, first Oct 22
- Saint Patrick, MO 63466 · last Apr 17, first Oct 22
- Knox City, MO 63446 · last Apr 17, first Oct 19
- Gorin, MO 63543 · last Apr 23, first Oct 17
Frequently asked questions
- When is the last frost in Williamstown, MO?
- For ZIP code 63473, the average last spring frost (32°F) is April 17, based on NOAA 1991-2020 climate normals for the Steffenville, MO weather station. There is a 1-in-10 chance of a frost after May 4.
- When is the first frost in Williamstown, MO?
- The average first fall frost (32°F) is October 19. There is a 1-in-10 chance of frost by September 30, so tender plants are at risk from that point on.
- How long is the growing season in 63473?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 184 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.