Frost dates for 97914Ontario, OR
The average last spring frost in Ontario is April 22 and the average first fall frost is October 9, giving a typical growing season of about 168 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 22
- Average first fall frost
- Oct 9
- Growing season
- 168 days
Safer after May 7 (1-in-10 risk)
Possible by Sep 26 (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 21 · May 5 · May 21 | Sep 16 · Sep 30 · Oct 12 | 145 days | 100% |
| Frost / freeze (32°F) | Apr 7 · Apr 22 · May 7 | Sep 26 · Oct 9 · Oct 23 | 168 days | 100% |
| Hard freeze (28°F) | Mar 18 · Apr 6 · Apr 23 | Oct 6 · Oct 21 · Nov 4 | 196 days | 100% |
Planting calendar for Ontario
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 22 – May 28 |
| Tomatoes | Transplant outdoors | May 8 – Jun 19 |
| Peppers | Start seeds indoors | Mar 22 – Apr 22 |
| Peppers | Transplant outdoors | May 22 – Jun 22 |
| Eggplant | Start seeds indoors | Apr 8 – May 7 |
| Eggplant | Transplant outdoors | May 22 – Jun 22 |
| Cucumbers | Sow outdoors | May 22 – Jun 29 |
| Summer squash | Sow outdoors | May 8 – Jun 22 |
| Winter squash & pumpkins | Sow outdoors | May 22 – Jun 22 |
| Snap beans | Sow outdoors | May 8 – Jul 22 |
| Sweet corn | Sow outdoors | May 8 – Jun 19 |
| Watermelon & cantaloupe | Sow outdoors | May 22 – Jun 22 |
| Okra | Sow outdoors | May 15 – Jun 7 |
| Peas | Sow outdoors (spring) | Mar 22 – May 7 |
| Potatoes | Plant outdoors (spring) | Mar 22 – May 22 |
| Onions | Start seeds indoors (spring) | Feb 8 – Mar 7 |
| Onions | Transplant outdoors (spring) | Apr 8 – May 7 |
| Broccoli | Start seeds indoors (spring) | Mar 4 – Apr 7 |
| Broccoli | Transplant outdoors (spring) | Apr 8 – May 7 |
| Broccoli | Start seeds indoors (fall) | Jun 9 – Jun 19 |
| Broccoli | Transplant outdoors (fall) | Jul 9 – Jul 20 |
| Cabbage | Start seeds indoors (spring) | Feb 22 – Mar 22 |
| Cabbage | Transplant outdoors (spring) | Mar 22 – Apr 22 |
| Cabbage | Start seeds indoors (fall) | May 30 – Jun 29 |
| Cabbage | Transplant outdoors (fall) | Jun 29 – Jul 30 |
| Leaf lettuce | Sow outdoors (spring) | Mar 22 – Jun 7 |
| Leaf lettuce | Sow outdoors (fall) | Jun 29 – Aug 15 |
| Spinach | Sow outdoors (spring) | Mar 15 – Apr 28 |
| Spinach | Sow outdoors (fall) | Jul 16 – Aug 20 |
| Radishes | Sow outdoors (spring) | Mar 22 – May 12 |
| Radishes | Sow outdoors (fall) | Jun 29 – Aug 30 |
| Kale | Sow outdoors (spring) | Apr 8 – Apr 28 |
| Kale | Sow outdoors (fall) | Jun 22 – Jul 30 |
| Carrots | Sow outdoors (spring) | Apr 22 – Jun 7 |
| Carrots | Sow outdoors (fall) | May 30 – Jul 15 |
| Garlic | Plant outdoors (fall) | Sep 29 – Oct 30 |
Where these dates come from
ZIP code 97914 is matched to the NOAA station Ontario Ksrv, OR, 0.6 km away, at 2,145 ft elevation (1 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Ontario Ksrv, OR (used) | 2,145 ft | Apr 22 | Oct 9 |
| Ontario Muni Ap, OR | 2,190 ft | Apr 21 | Oct 14 |
| Payette, ID | 2,150 ft | Apr 19 | Oct 20 |
| Malheur Branch Exp Stn, OR | 2,260 ft | Apr 23 | Oct 13 |
Frost dates near Ontario
- Payette, ID 83661 · last Apr 19, first Oct 20
- Fruitland, ID 83619 · last Apr 21, first Oct 14
- New Plymouth, ID 83655 · last Apr 23, first Oct 13
- Nyssa, OR 97913 · last Apr 18, first Oct 18
- Weiser, ID 83672 · last Apr 23, first Oct 13
- Vale, OR 97918 · last May 8, first Sep 29
- Parma, ID 83660 · last Apr 27, first Oct 9
- Letha, ID 83636 · last Apr 30, first Oct 17
Frequently asked questions
- When is the last frost in Ontario, OR?
- For ZIP code 97914, the average last spring frost (32°F) is April 22, based on NOAA 1991-2020 climate normals for the Ontario Ksrv, OR weather station. There is a 1-in-10 chance of a frost after May 7.
- When is the first frost in Ontario, OR?
- The average first fall frost (32°F) is October 9. There is a 1-in-10 chance of frost by September 26, so tender plants are at risk from that point on.
- How long is the growing season in 97914?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 168 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.