Frost dates for 97838Hermiston, OR
The average last spring frost in Hermiston is April 27 and the average first fall frost is October 7, giving a typical growing season of about 163 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 27
- Average first fall frost
- Oct 7
- Growing season
- 163 days
Safer after May 11 (1-in-10 risk)
Possible by Sep 25 (1-in-10 risk)
Last frost typically in 177 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 29 · May 11 · May 26 | Sep 11 · Sep 26 · Oct 9 | 136 days | 100% |
| Frost / freeze (32°F) | Apr 11 · Apr 27 · May 11 | Sep 25 · Oct 7 · Oct 21 | 163 days | 100% |
| Hard freeze (28°F) | Mar 25 · Apr 10 · Apr 29 | Oct 5 · Oct 20 · Nov 2 | 193 days | 100% |
Planting calendar for Hermiston
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 27 – Jun 2 |
| Tomatoes | Transplant outdoors | May 13 – Jun 17 |
| Peppers | Start seeds indoors | Mar 27 – Apr 27 |
| Peppers | Transplant outdoors | May 27 – Jun 27 |
| Eggplant | Start seeds indoors | Apr 13 – May 12 |
| Eggplant | Transplant outdoors | May 27 – Jun 27 |
| Cucumbers | Sow outdoors | May 27 – Jun 27 |
| Summer squash | Sow outdoors | May 13 – Jun 27 |
| Winter squash & pumpkins | Sow outdoors | May 27 – Jun 27 |
| Snap beans | Sow outdoors | May 13 – Jul 20 |
| Sweet corn | Sow outdoors | May 13 – Jun 17 |
| Watermelon & cantaloupe | Sow outdoors | May 27 – Jun 27 |
| Okra | Sow outdoors | May 20 – Jun 12 |
| Peas | Sow outdoors (spring) | Mar 27 – May 12 |
| Potatoes | Plant outdoors (spring) | Mar 27 – May 27 |
| Onions | Start seeds indoors (spring) | Feb 13 – Mar 12 |
| Onions | Transplant outdoors (spring) | Apr 13 – May 12 |
| Broccoli | Start seeds indoors (spring) | Mar 9 – Apr 12 |
| Broccoli | Transplant outdoors (spring) | Apr 13 – May 12 |
| Broccoli | Start seeds indoors (fall) | Jun 7 – Jun 17 |
| Broccoli | Transplant outdoors (fall) | Jul 7 – Jul 18 |
| Cabbage | Start seeds indoors (spring) | Feb 27 – Mar 27 |
| Cabbage | Transplant outdoors (spring) | Mar 27 – Apr 27 |
| Cabbage | Start seeds indoors (fall) | May 28 – Jun 27 |
| Cabbage | Transplant outdoors (fall) | Jun 27 – Jul 28 |
| Leaf lettuce | Sow outdoors (spring) | Mar 27 – Jun 12 |
| Leaf lettuce | Sow outdoors (fall) | Jun 27 – Aug 13 |
| Spinach | Sow outdoors (spring) | Mar 20 – May 3 |
| Spinach | Sow outdoors (fall) | Jul 14 – Aug 18 |
| Radishes | Sow outdoors (spring) | Mar 27 – May 17 |
| Radishes | Sow outdoors (fall) | Jun 27 – Aug 28 |
| Kale | Sow outdoors (spring) | Apr 13 – May 3 |
| Kale | Sow outdoors (fall) | Jun 20 – Jul 28 |
| Carrots | Sow outdoors (spring) | Apr 27 – Jun 12 |
| Carrots | Sow outdoors (fall) | May 28 – Jul 13 |
| Garlic | Plant outdoors (fall) | Sep 27 – Oct 28 |
Where these dates come from
ZIP code 97838 is matched to the NOAA station Hermiston 2 Nw, OR, 2.8 km away, at 460 ft elevation (14 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Hermiston 2 Nw, OR (used) | 460 ft | Apr 27 | Oct 7 |
| Hermiston Muni Ap, OR | 641 ft | Apr 26 | Oct 10 |
| Mcnary Dam #2, OR | 361 ft | Mar 30 | Nov 4 |
| Mcnary Dam, WA | 361 ft | Mar 27 | Nov 4 |
Frost dates near Hermiston
- Umatilla, OR 97882 · last Apr 27, first Oct 7
- Stanfield, OR 97875 · last Apr 26, first Oct 10
- Plymouth, WA 99346 · last Mar 27, first Nov 4
- Echo, OR 97826 · last Apr 26, first Oct 10
- Irrigon, OR 97844 · last Apr 14, first Oct 21
- Boardman, OR 97818 · last Apr 14, first Oct 21
- Kennewick, WA 99338 · last Mar 28, first Oct 30
- Wallula, WA 99363 · last Apr 7, first Oct 22
Frequently asked questions
- When is the last frost in Hermiston, OR?
- For ZIP code 97838, the average last spring frost (32°F) is April 27, based on NOAA 1991-2020 climate normals for the Hermiston 2 Nw, OR weather station. There is a 1-in-10 chance of a frost after May 11.
- When is the first frost in Hermiston, OR?
- The average first fall frost (32°F) is October 7. There is a 1-in-10 chance of frost by September 25, so tender plants are at risk from that point on.
- How long is the growing season in 97838?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 163 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.