Frost dates for 97906Harper, OR
The average last spring frost in Harper is May 7 and the average first fall frost is October 5, giving a typical growing season of about 150 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 7
- Average first fall frost
- Oct 5
- Growing season
- 150 days
Safer after May 27 (1-in-10 risk)
Possible by Sep 19 (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 9 · May 29 · Jun 19 | Sep 6 · Sep 21 · Oct 5 | 114 days | 100% |
| Frost / freeze (32°F) | Apr 23 · May 7 · May 27 | Sep 19 · Oct 5 · Oct 20 | 150 days | 100% |
| Hard freeze (28°F) | Apr 2 · Apr 21 · May 7 | Oct 3 · Oct 18 · Nov 1 | 179 days | 100% |
Planting calendar for Harper
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 6 – Jun 12 |
| Tomatoes | Transplant outdoors | May 23 – Jun 15 |
| Peppers | Start seeds indoors | Apr 6 – May 7 |
| Peppers | Transplant outdoors | Jun 6 – Jul 7 |
| Eggplant | Start seeds indoors | Apr 23 – May 22 |
| Eggplant | Transplant outdoors | Jun 6 – Jul 7 |
| Cucumbers | Sow outdoors | Jun 6 – Jun 25 |
| Summer squash | Sow outdoors | May 23 – Jul 7 |
| Winter squash & pumpkins | Sow outdoors | Jun 6 – Jul 7 |
| Snap beans | Sow outdoors | May 23 – Jul 18 |
| Sweet corn | Sow outdoors | May 23 – Jun 15 |
| Watermelon & cantaloupe | Sow outdoors | Jun 6 – Jul 7 |
| Okra | Sow outdoors | May 30 – Jun 22 |
| Peas | Sow outdoors (spring) | Apr 6 – May 22 |
| Potatoes | Plant outdoors (spring) | Apr 6 – Jun 6 |
| Onions | Start seeds indoors (spring) | Feb 23 – Mar 22 |
| Onions | Transplant outdoors (spring) | Apr 23 – May 22 |
| Broccoli | Start seeds indoors (spring) | Mar 19 – Apr 22 |
| Broccoli | Transplant outdoors (spring) | Apr 23 – May 22 |
| Broccoli | Start seeds indoors (fall) | Jun 5 – Jun 15 |
| Broccoli | Transplant outdoors (fall) | Jul 5 – Jul 16 |
| Cabbage | Start seeds indoors (spring) | Mar 9 – Apr 6 |
| Cabbage | Transplant outdoors (spring) | Apr 6 – May 7 |
| Cabbage | Start seeds indoors (fall) | May 26 – Jun 25 |
| Cabbage | Transplant outdoors (fall) | Jun 25 – Jul 26 |
| Leaf lettuce | Sow outdoors (spring) | Apr 6 – Jun 22 |
| Leaf lettuce | Sow outdoors (fall) | Jun 25 – Aug 11 |
| Spinach | Sow outdoors (spring) | Mar 30 – May 13 |
| Spinach | Sow outdoors (fall) | Jul 12 – Aug 16 |
| Radishes | Sow outdoors (spring) | Apr 6 – May 27 |
| Radishes | Sow outdoors (fall) | Jun 25 – Aug 26 |
| Kale | Sow outdoors (spring) | Apr 23 – May 13 |
| Kale | Sow outdoors (fall) | Jun 18 – Jul 26 |
| Carrots | Sow outdoors (spring) | May 7 – Jun 22 |
| Carrots | Sow outdoors (fall) | May 26 – Jul 11 |
| Garlic | Plant outdoors (fall) | Sep 25 – Oct 26 |
Where these dates come from
ZIP code 97906 is matched to the NOAA station Owyhee Dam, OR, 33.6 km away, at 2,400 ft elevation (162 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Owyhee Dam, OR (used) | 2,400 ft | May 7 | Oct 5 |
| Westfall, OR | 3,040 ft | May 7 | Oct 3 |
| Vale, OR | 2,240 ft | May 8 | Sep 29 |
| Malheur Branch Exp Stn, OR | 2,260 ft | Apr 23 | Oct 13 |
Frost dates near Harper
- Westfall, OR 97920 · last May 7, first Oct 3
- Vale, OR 97918 · last May 8, first Sep 29
- Brogan, OR 97903 · last May 7, first Oct 3
- Jamieson, OR 97909 · last Apr 23, first Oct 13
- Nyssa, OR 97913 · last Apr 18, first Oct 18
- Adrian, OR 97901 · last Apr 24, first Oct 9
- Juntura, OR 97911 · last Jun 5, first Sep 5
- Ontario, OR 97914 · last Apr 22, first Oct 9
Frequently asked questions
- When is the last frost in Harper, OR?
- For ZIP code 97906, the average last spring frost (32°F) is May 7, based on NOAA 1991-2020 climate normals for the Owyhee Dam, OR weather station. There is a 1-in-10 chance of a frost after May 27.
- When is the first frost in Harper, OR?
- The average first fall frost (32°F) is October 5. There is a 1-in-10 chance of frost by September 19, so tender plants are at risk from that point on.
- How long is the growing season in 97906?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 150 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.