Frost dates for 97124Hillsboro, OR
The average last spring frost in Hillsboro is April 16 and the average first fall frost is October 23, giving a typical growing season of about 191 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 16
- Average first fall frost
- Oct 23
- Growing season
- 191 days
Safer after May 3 (1-in-10 risk)
Possible by Oct 3 (1-in-10 risk)
Last frost typically in 168 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 27 | Sep 20 · Oct 6 · Oct 31 | 153 days | 100% |
| Frost / freeze (32°F) | Mar 25 · Apr 16 · May 3 | Oct 3 · Oct 23 · Nov 18 | 191 days | 100% |
| Hard freeze (28°F) | Feb 15 · Mar 13 · Apr 9 | Oct 20 · Nov 12 · Dec 10 | 243 days | 100% |
Planting calendar for Hillsboro
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 16 – May 22 |
| Tomatoes | Transplant outdoors | May 2 – Jul 3 |
| Peppers | Start seeds indoors | Mar 16 – Apr 16 |
| Peppers | Transplant outdoors | May 16 – Jun 16 |
| Eggplant | Start seeds indoors | Apr 2 – May 1 |
| Eggplant | Transplant outdoors | May 16 – Jun 16 |
| Cucumbers | Sow outdoors | May 16 – Jul 13 |
| Summer squash | Sow outdoors | May 2 – Jun 16 |
| Winter squash & pumpkins | Sow outdoors | May 16 – Jun 16 |
| Snap beans | Sow outdoors | May 2 – Aug 5 |
| Sweet corn | Sow outdoors | May 2 – Jul 3 |
| Watermelon & cantaloupe | Sow outdoors | May 16 – Jun 16 |
| Okra | Sow outdoors | May 9 – Jun 1 |
| Peas | Sow outdoors (spring) | Mar 16 – May 1 |
| Potatoes | Plant outdoors (spring) | Mar 16 – May 16 |
| Onions | Start seeds indoors (spring) | Feb 2 – Mar 1 |
| Onions | Transplant outdoors (spring) | Apr 2 – May 1 |
| Broccoli | Start seeds indoors (spring) | Feb 26 – Apr 1 |
| Broccoli | Transplant outdoors (spring) | Apr 2 – May 1 |
| Broccoli | Start seeds indoors (fall) | Jun 23 – Jul 3 |
| Broccoli | Transplant outdoors (fall) | Jul 23 – Aug 3 |
| Cabbage | Start seeds indoors (spring) | Feb 16 – Mar 16 |
| Cabbage | Transplant outdoors (spring) | Mar 16 – Apr 16 |
| Cabbage | Start seeds indoors (fall) | Jun 13 – Jul 13 |
| Cabbage | Transplant outdoors (fall) | Jul 13 – Aug 13 |
| Leaf lettuce | Sow outdoors (spring) | Mar 16 – Jun 1 |
| Leaf lettuce | Sow outdoors (fall) | Jul 13 – Aug 29 |
| Spinach | Sow outdoors (spring) | Mar 9 – Apr 22 |
| Spinach | Sow outdoors (fall) | Jul 30 – Sep 3 |
| Radishes | Sow outdoors (spring) | Mar 16 – May 6 |
| Radishes | Sow outdoors (fall) | Jul 13 – Sep 13 |
| Kale | Sow outdoors (spring) | Apr 2 – Apr 22 |
| Kale | Sow outdoors (fall) | Jul 6 – Aug 13 |
| Carrots | Sow outdoors (spring) | Apr 16 – Jun 1 |
| Carrots | Sow outdoors (fall) | Jun 13 – Jul 29 |
| Garlic | Plant outdoors (fall) | Oct 13 – Nov 13 |
Where these dates come from
ZIP code 97124 is matched to the NOAA station Portland-Hillsboro Ap, OR, 1.2 km away, at 204 ft elevation (4 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Portland-Hillsboro Ap, OR (used) | 204 ft | Apr 16 | Oct 23 |
| Nature Park-Beaverton, OR | 185 ft | Feb 11 | Dec 5 |
| Forest Grove, OR | 180 ft | Apr 16 | Oct 26 |
| Beaverton 2 Ssw, OR | 270 ft | Apr 1 | Nov 6 |
Frost dates near Hillsboro
- Hillsboro, OR 97129 · last Apr 16, first Oct 23
- Cornelius, OR 97113 · last Apr 16, first Oct 26
- Beaverton, OR 97003 · last Apr 16, first Oct 23
- Portland, OR 97229 · last Apr 16, first Oct 23
- North Plains, OR 97133 · last May 8, first Oct 1
- Banks, OR 97106 · last Apr 16, first Oct 26
- Forest Grove, OR 97116 · last Apr 16, first Oct 26
- Gaston, OR 97119 · last Apr 16, first Oct 26
Frequently asked questions
- When is the last frost in Hillsboro, OR?
- For ZIP code 97124, the average last spring frost (32°F) is April 16, based on NOAA 1991-2020 climate normals for the Portland-Hillsboro Ap, OR weather station. There is a 1-in-10 chance of a frost after May 3.
- When is the first frost in Hillsboro, OR?
- The average first fall frost (32°F) is October 23. There is a 1-in-10 chance of frost by October 3, so tender plants are at risk from that point on.
- How long is the growing season in 97124?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 191 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.