Hillsboro, Oregon: planting zone & frost dates
Hillsboro is in USDA plant hardiness zone 8b, where the average coldest winter night reaches 15 to 20°F (-9.4 to -6.7°C). The typical last spring frost is around Apr 25 and the first fall frost around Oct 14.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 3 | Oct 3 |
| Typical planning date (30% risk) | Apr 25 | Oct 14 |
| Median (50%) | Apr 16 | Oct 23 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station PORTLAND-HILLSBORO AP, OR (USW00094261), 1.1 mi (1.8 km) from the city center and 26 ft higher than the city center (+8 m). Record used for the 1991–2020 normals: 20 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Hillsboro
All 3 ZIP codes covering Hillsboro are in zone 8b.
Vegetable planting calendar for Hillsboro
Dates are counted from the 30%-risk frost dates above (last frost Apr 25, first frost Oct 14). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Feb 28 – Mar 14 | May 2 – May 16 | — | — |
| Pepper | Feb 14 – Feb 28 | May 9 – May 23 | — | — |
| Lettuce | Mar 14 – Mar 28 | Apr 11 – May 2 | Mar 28 – May 9 | Aug 5 – Sep 2 |
| Green Beans | — | — | May 2 – Jun 6 | Jul 22 – Aug 5 |
| Sweet Corn | — | — | May 2 – May 30 | — |
| Zucchini & Summer Squash | Mar 28 – Apr 4 | May 2 – May 16 | May 2 – May 23 | Jul 22 – Aug 5 |
| Cucumber | Mar 28 – Apr 4 | May 9 – May 16 | May 2 – May 23 | Jul 22 – Aug 5 |
| Carrot | — | — | Apr 4 – May 9 | Jul 22 – Aug 5 |
| Onion | Jan 31 – Feb 14 | Mar 28 – Apr 11 | — | — |
| Potato | — | Mar 28 – Apr 18 | — | — |
| Basil | Mar 14 – Mar 28 | May 9 – May 23 | May 9 – May 30 | — |
| Spinach | — | — | Mar 14 – Apr 11 | Aug 19 – Sep 16 |
| Kale | Feb 28 – Mar 14 | Mar 28 – Apr 18 | Mar 28 – Apr 18 | Aug 5 – Sep 2 |
| Broccoli | Feb 28 – Mar 14 | Apr 11 – May 2 | — | Jul 22 – Aug 5 |
| Peas | — | — | Mar 14 – Apr 4 | Aug 5 – Aug 19 |
| Eggplant | Feb 14 – Feb 28 | May 9 – May 23 | — | — |
| Cabbage | Feb 28 – Mar 14 | Mar 28 – Apr 11 | — | Jul 22 – Aug 5 |
| Radish | — | — | Mar 21 – May 9 | Sep 2 – Sep 30 |
| Strawberry | — | Mar 28 – Apr 18 | — | — |
| Beets | — | — | Apr 4 – May 16 | Aug 5 – Aug 19 |
Nearby cities in Oregon
- Beaverton — zone 9a, last frost Apr 11, first frost Oct 29
- Portland — zone 9a, last frost Mar 6, first frost Nov 22
- Gresham — zone 9a, last frost Mar 27, first frost Nov 9
- Salem — zone 8b, last frost Apr 13, first frost Oct 26
- Eugene — zone 8b, last frost Apr 25, first frost Oct 15
- Bend — zone 6b, last frost Jun 14, first frost Sep 12
More: all Oregon cities · other zone 8b cities: Dallas, TX, Fort Worth, TX, El Paso, TX, Virginia Beach, VA, Arlington, TX, Plano, TX, Irving, TX, Garland, TX
Hillsboro gardening questions
When is the last frost in Hillsboro, OR?
Plan around Apr 25. At NOAA's Portland-hillsboro Airport, OR station, 1.1 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 16, and after May 3 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Mar 13. The 90% and 10% dates are 39 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Hillsboro, OR?
Start seeds indoors Feb 28 – Mar 14 and set transplants outside May 2 – May 16, once nights stay above 50°F and the soil is near 60°F. That leaves 172 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Hillsboro?
About 191 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 161 days, and in 1 year in 10 it runs 223 days or more. In fall there is a 10% chance of frost by Oct 3 and a 30% chance by Oct 14. That ranks 7th longest of 8 Oregon cities on this site.
When should I plant a fall garden in Hillsboro?
Count back from the first fall frost (Oct 14): transplant broccoli Jul 22 – Aug 5; sow kale Aug 5 – Sep 2; sow lettuce Aug 5 – Sep 2; sow radishes Sep 2 – Sep 30. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Nov 12. How the math works: succession and fall planting.
Did Hillsboro's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Hillsboro is zone 8b on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
How does Hillsboro compare with Beaverton, OR?
Hillsboro is zone 8b and Beaverton is zone 9a. The typical last spring frost in Hillsboro (Apr 25) comes about 14 days later than in Beaverton, OR (Apr 11), 7 miles away, and the first fall frost is Oct 14 versus Oct 29. The two cities use different NOAA stations.