Frost dates for 97883Union, OR
The average last spring frost in Union is May 11 and the average first fall frost is September 26, giving a typical growing season of about 136 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 11
- Average first fall frost
- Sep 26
- Growing season
- 136 days
Safer after May 31 (1-in-10 risk)
Possible by Sep 9 (1-in-10 risk)
Last frost typically in 190 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 14 · Jun 2 · Jun 23 | Aug 29 · Sep 10 · Sep 26 | 101 days | 100% |
| Frost / freeze (32°F) | Apr 26 · May 11 · May 31 | Sep 9 · Sep 26 · Oct 10 | 136 days | 100% |
| Hard freeze (28°F) | Apr 7 · Apr 24 · May 10 | Sep 23 · Oct 7 · Oct 23 | 166 days | 100% |
Planting calendar for Union
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 10 – Jun 16 |
| Tomatoes | Transplant outdoors | May 27 – Jun 6 |
| Peppers | Start seeds indoors | Apr 10 – May 11 |
| Peppers | Transplant outdoors | Jun 10 – Jul 11 |
| Eggplant | Start seeds indoors | Apr 27 – May 26 |
| Eggplant | Transplant outdoors | Jun 10 – Jul 11 |
| Cucumbers | Sow outdoors | Jun 10 – Jun 16 |
| Summer squash | Sow outdoors | May 27 – Jul 11 |
| Winter squash & pumpkins | Sow outdoors | Jun 10 – Jul 11 |
| Snap beans | Sow outdoors | May 27 – Jul 9 |
| Sweet corn | Sow outdoors | May 27 – Jun 6 |
| Watermelon & cantaloupe | Sow outdoors | Jun 10 – Jul 11 |
| Okra | Sow outdoors | Jun 3 – Jun 26 |
| Peas | Sow outdoors (spring) | Apr 10 – May 26 |
| Potatoes | Plant outdoors (spring) | Apr 10 – Jun 10 |
| Onions | Start seeds indoors (spring) | Feb 27 – Mar 26 |
| Onions | Transplant outdoors (spring) | Apr 27 – May 26 |
| Broccoli | Start seeds indoors (spring) | Mar 23 – Apr 26 |
| Broccoli | Transplant outdoors (spring) | Apr 27 – May 26 |
| Broccoli | Start seeds indoors (fall) | May 27 – Jun 6 |
| Broccoli | Transplant outdoors (fall) | Jun 26 – Jul 7 |
| Cabbage | Start seeds indoors (spring) | Mar 13 – Apr 10 |
| Cabbage | Transplant outdoors (spring) | Apr 10 – May 11 |
| Cabbage | Start seeds indoors (fall) | May 17 – Jun 16 |
| Cabbage | Transplant outdoors (fall) | Jun 16 – Jul 17 |
| Leaf lettuce | Sow outdoors (spring) | Apr 10 – Jun 26 |
| Leaf lettuce | Sow outdoors (fall) | Jun 16 – Aug 2 |
| Spinach | Sow outdoors (spring) | Apr 3 – May 17 |
| Spinach | Sow outdoors (fall) | Jul 3 – Aug 7 |
| Radishes | Sow outdoors (spring) | Apr 10 – May 31 |
| Radishes | Sow outdoors (fall) | Jun 16 – Aug 17 |
| Kale | Sow outdoors (spring) | Apr 27 – May 17 |
| Kale | Sow outdoors (fall) | Jun 9 – Jul 17 |
| Carrots | Sow outdoors (spring) | May 11 – Jun 26 |
| Carrots | Sow outdoors (fall) | May 17 – Jul 2 |
| Garlic | Plant outdoors (fall) | Sep 16 – Oct 17 |
Where these dates come from
ZIP code 97883 is matched to the NOAA station Union, OR, 0.9 km away, at 2,777 ft elevation (120 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Union, OR (used) | 2,777 ft | May 11 | Sep 26 |
| La Grande, OR | 2,755 ft | May 6 | Oct 1 |
| Baker City Muni Ap, OR | 3,361 ft | May 25 | Sep 15 |
| Elgin, OR | 2,697 ft | May 24 | Sep 18 |
Frost dates near Union
- Cove, OR 97824 · last May 11, first Sep 26
- North Powder, OR 97867 · last May 25, first Sep 15
- La Grande, OR 97850 · last May 6, first Oct 1
- Imbler, OR 97841 · last May 6, first Oct 1
- Summerville, OR 97876 · last May 6, first Oct 1
- Haines, OR 97833 · last May 25, first Sep 15
- Elgin, OR 97827 · last May 24, first Sep 18
- Lostine, OR 97857 · last Jun 7, first Sep 9
Frequently asked questions
- When is the last frost in Union, OR?
- For ZIP code 97883, the average last spring frost (32°F) is May 11, based on NOAA 1991-2020 climate normals for the Union, OR weather station. There is a 1-in-10 chance of a frost after May 31.
- When is the first frost in Union, OR?
- The average first fall frost (32°F) is September 26. There is a 1-in-10 chance of frost by September 9, so tender plants are at risk from that point on.
- How long is the growing season in 97883?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 136 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.