Frost dates for 99139Ione, WA
The average last spring frost in Ione is May 4 and the average first fall frost is October 4, giving a typical growing season of about 153 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 4
- Average first fall frost
- Oct 4
- Growing season
- 153 days
Safer after May 18 (1-in-10 risk)
Possible by Sep 21 (1-in-10 risk)
Last frost typically in 186 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 6 · May 19 · Jun 2 | Sep 4 · Sep 21 · Oct 5 | 123 days | 100% |
| Frost / freeze (32°F) | Apr 20 · May 4 · May 18 | Sep 21 · Oct 4 · Oct 20 | 153 days | 100% |
| Hard freeze (28°F) | Apr 1 · Apr 17 · May 2 | Oct 1 · Oct 19 · Nov 4 | 184 days | 100% |
Planting calendar for Ione
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 99139 is matched to the NOAA station Boundary Dam, WA, 28.6 km away, at 1,837 ft elevation (243 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Boundary Dam, WA (used) | 1,837 ft | May 4 | Oct 4 |
| Northport, WA | 1,497 ft | May 8 | Oct 1 |
| Colville, WA | 1,554 ft | May 2 | Oct 2 |
| Chewelah, WA | 1,670 ft | May 16 | Sep 15 |
Frost dates near Ione
- Metaline, WA 99152 · last May 4, first Oct 4
- Metaline Falls, WA 99153 · last May 4, first Oct 4
- Northport, WA 99157 · last May 8, first Oct 1
- Nordman, ID 83848 · last May 20, first Sep 13
- Colville, WA 99114 · last May 2, first Oct 2
- Cusick, WA 99119 · last May 12, first Sep 21
- Evans, WA 99126 · last May 2, first Oct 2
- Kettle Falls, WA 99141 · last May 2, first Oct 2
Frequently asked questions
- When is the last frost in Ione, WA?
- For ZIP code 99139, the average last spring frost (32°F) is May 4, based on NOAA 1991-2020 climate normals for the Boundary Dam, WA weather station. There is a 1-in-10 chance of a frost after May 18.
- When is the first frost in Ione, WA?
- The average first fall frost (32°F) is October 4. There is a 1-in-10 chance of frost by September 21, so tender plants are at risk from that point on.
- How long is the growing season in 99139?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 153 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.