Frost Dates for Hillsboro, OR
In Hillsboro, OR, the average last spring frost is around Apr 16 and the average first fall frost around Oct 23, for a growing season of about 191 days. For frost-tender plants, wait until May 3, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Portland-Hillsboro Airport, OR weather station, 1 mile away, elevation 204 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | May 3 | Oct 3 |
| 20% | Apr 29 | Oct 9 |
| 30% | Apr 25 | Oct 14 |
| 40% | Apr 20 | Oct 18 |
| 50% | Apr 16 | Oct 23 |
| 60% | Apr 11 | Oct 28 |
| 70% | Apr 5 | Nov 2 |
| 80% | Mar 31 | Nov 8 |
| 90% | Mar 25 | Nov 18 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | May 5 | Oct 6 |
| Frost / freeze (32°F) | Apr 16 | Oct 23 |
| Hard freeze (28°F) | Mar 13 | Nov 12 |
Planting calendar for Hillsboro
Transplant Apr 23 – May 7
Transplant Apr 30 – May 14
Transplant Apr 30 – May 14
Transplant Apr 23 – May 7
Sow or transplant Apr 23 – May 7
Sow or transplant Apr 23 – May 7
Sow or transplant Apr 30 – May 14
Sow or transplant Mar 19 – Apr 2
Fall sowing Aug 28 – Sep 25
Fall sowing Aug 28 – Sep 18
Fall sowing Aug 14 – Aug 28
Sow or transplant Mar 19 – Apr 2
Fall sowing Aug 14 – Sep 11
Transplant Apr 2 – Apr 16
Fall sowing Jul 31 – Aug 14
Transplant Mar 26 – Apr 9
Fall sowing Jul 31 – Aug 14
Fall sowing Jul 31 – Aug 14
Fall sowing Sep 11 – Oct 2
Fall sowing Aug 14 – Aug 28
Plant Mar 19 – Apr 2
Based on the average last frost (Apr 16) and first frost (Oct 23). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.