Frost dates for 99357Royal City, WA
The average last spring frost in Royal City is April 23 and the average first fall frost is October 12, giving a typical growing season of about 172 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 23
- Average first fall frost
- Oct 12
- Growing season
- 172 days
Safer after May 7 (1-in-10 risk)
Possible by Oct 1 (1-in-10 risk)
Last frost typically in 171 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 23 · May 6 · May 18 | Sep 21 · Oct 2 · Oct 14 | 148 days | 100% |
| Frost / freeze (32°F) | Apr 3 · Apr 23 · May 7 | Oct 1 · Oct 12 · Oct 25 | 172 days | 100% |
| Hard freeze (28°F) | Mar 13 · Apr 3 · Apr 24 | Oct 6 · Oct 24 · Nov 6 | 202 days | 100% |
Planting calendar for Royal City
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 23 – May 29 |
| Tomatoes | Transplant outdoors | May 9 – Jun 22 |
| Peppers | Start seeds indoors | Mar 23 – Apr 23 |
| Peppers | Transplant outdoors | May 23 – Jun 23 |
| Eggplant | Start seeds indoors | Apr 9 – May 8 |
| Eggplant | Transplant outdoors | May 23 – Jun 23 |
| Cucumbers | Sow outdoors | May 23 – Jul 2 |
| Summer squash | Sow outdoors | May 9 – Jun 23 |
| Winter squash & pumpkins | Sow outdoors | May 23 – Jun 23 |
| Snap beans | Sow outdoors | May 9 – Jul 25 |
| Sweet corn | Sow outdoors | May 9 – Jun 22 |
| Watermelon & cantaloupe | Sow outdoors | May 23 – Jun 23 |
| Okra | Sow outdoors | May 16 – Jun 8 |
| Peas | Sow outdoors (spring) | Mar 23 – May 8 |
| Potatoes | Plant outdoors (spring) | Mar 23 – May 23 |
| Onions | Start seeds indoors (spring) | Feb 9 – Mar 8 |
| Onions | Transplant outdoors (spring) | Apr 9 – May 8 |
| Broccoli | Start seeds indoors (spring) | Mar 5 – Apr 8 |
| Broccoli | Transplant outdoors (spring) | Apr 9 – May 8 |
| Broccoli | Start seeds indoors (fall) | Jun 12 – Jun 22 |
| Broccoli | Transplant outdoors (fall) | Jul 12 – Jul 23 |
| Cabbage | Start seeds indoors (spring) | Feb 23 – Mar 23 |
| Cabbage | Transplant outdoors (spring) | Mar 23 – Apr 23 |
| Cabbage | Start seeds indoors (fall) | Jun 2 – Jul 2 |
| Cabbage | Transplant outdoors (fall) | Jul 2 – Aug 2 |
| Leaf lettuce | Sow outdoors (spring) | Mar 23 – Jun 8 |
| Leaf lettuce | Sow outdoors (fall) | Jul 2 – Aug 18 |
| Spinach | Sow outdoors (spring) | Mar 16 – Apr 29 |
| Spinach | Sow outdoors (fall) | Jul 19 – Aug 23 |
| Radishes | Sow outdoors (spring) | Mar 23 – May 13 |
| Radishes | Sow outdoors (fall) | Jul 2 – Sep 2 |
| Kale | Sow outdoors (spring) | Apr 9 – Apr 29 |
| Kale | Sow outdoors (fall) | Jun 25 – Aug 2 |
| Carrots | Sow outdoors (spring) | Apr 23 – Jun 8 |
| Carrots | Sow outdoors (fall) | Jun 2 – Jul 18 |
| Garlic | Plant outdoors (fall) | Oct 2 – Nov 2 |
Where these dates come from
ZIP code 99357 is matched to the NOAA station Smyrna, WA, 10.8 km away, at 560 ft elevation (582 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Smyrna, WA (used) | 560 ft | Apr 23 | Oct 12 |
| Moses Lake Grant Co Ap, WA | 1,196 ft | Apr 27 | Oct 8 |
| Priest Rapids Dam, WA | 428 ft | Mar 24 | Nov 4 |
| Quincy, WA | 1,286 ft | Apr 21 | Oct 16 |
Frost dates near Royal City
- Mattawa, WA 99349 · last Apr 23, first Oct 12
- Beverly, WA 99321 · last Apr 23, first Oct 12
- George, WA 98824 · last Apr 21, first Oct 16
- Vantage, WA 98950 · last Apr 23, first Oct 12
- Moses Lake, WA 98837 · last Apr 27, first Oct 8
- Quincy, WA 98848 · last Apr 21, first Oct 16
- Ephrata, WA 98823 · last Apr 22, first Oct 17
- Warden, WA 98857 · last Apr 27, first Oct 8
Frequently asked questions
- When is the last frost in Royal City, WA?
- For ZIP code 99357, the average last spring frost (32°F) is April 23, based on NOAA 1991-2020 climate normals for the Smyrna, WA weather station. There is a 1-in-10 chance of a frost after May 7.
- When is the first frost in Royal City, WA?
- The average first fall frost (32°F) is October 12. 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 99357?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 172 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.