Hillsboro, OR planting zone & frost dates
Hillsboro is in USDA hardiness zone 8b. The last spring frost usually comes around April 16 and the first fall frost around October 23, for a growing season of about 191 days.
Planting calendar for Hillsboro
Dates are counted from the average last spring frost (April 16) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Feb 19 – Mar 5 Transplant outdoors: Apr 23 – Apr 30 |
| Peppers | Start seeds indoors: Feb 5 – Feb 19 Transplant outdoors: Apr 30 – May 7 |
| Eggplant | Start seeds indoors: Feb 5 – Feb 19 Transplant outdoors: Apr 30 – May 7 |
| Broccoli | Start seeds indoors: Feb 5 – Feb 19 Transplant outdoors: Mar 19 – Apr 2 |
| Cabbage | Start seeds indoors: Feb 5 – Feb 19 Transplant outdoors: Mar 19 – Apr 2 |
| Onions (sets) | Plant outdoors: Mar 19 – Apr 2 |
| Peas | Sow outdoors: Mar 5 – Mar 19 |
| Spinach | Sow outdoors: Mar 5 – Mar 19 |
| Lettuce | Sow outdoors: Mar 19 – Apr 2 |
| Carrots | Sow outdoors: Mar 19 – Apr 2 |
| Potatoes | Plant outdoors: Mar 19 – Apr 2 |
| Beans | Sow outdoors: Apr 23 – Apr 30 |
| Sweet corn | Sow outdoors: Apr 23 – Apr 30 |
| Cucumbers | Sow outdoors: Apr 23 – Apr 30 |
| Squash & zucchini | Sow outdoors: Apr 23 – Apr 30 |
| Basil | Start seeds indoors: Mar 5 – Mar 19 Transplant outdoors: Apr 23 – Apr 30 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 28 (8 weeks before the average first fall frost on Oct 23).
Useful for zone 8b gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Mar 25 | Apr 16 | May 3 |
| First 32°F frost in fall is before | Nov 18 | Oct 23 | Oct 3 |
How to read it: in spring there is a 10% chance of a frost after May 3, so that is a safe date for tender plants. In fall there is a 10% chance of frost before October 3. A hard freeze (28°F) usually ends around March 13.
Hardiness zone by ZIP code in Hillsboro
- 97123 zone 8b
- 97124 zone 8b
- 97129 zone 8b
Nearby cities
- Cornelius zone 8b, last frost Apr 16
- Forest Grove zone 8b, last frost Apr 16
- Aloha zone 9a, last frost Feb 11
- Bethany zone 8b, last frost Apr 16
- Oak Hills zone 8b, last frost Feb 11
- Cedar Mill zone 8b, last frost Feb 11
- Beaverton zone 9a, last frost Feb 11
- Newberg zone 8b, last frost Mar 21
Questions
What growing zone is Hillsboro, OR?
Hillsboro is in USDA Plant Hardiness Zone 8b (average extreme winter low 15°F to 20°F), according to the USDA 2023 map.
When is the last frost in Hillsboro?
The average last spring frost (32°F) in Hillsboro is April 16. There is still a 10% chance of frost until May 3.
When can I plant tomatoes in Hillsboro?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Apr 23 – Apr 30. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Portland-Hillsboro Ap, OR (USW00094261), 3.8 km (2.4 mi) from the city center, elevation 62 m, based on 20 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.