Frost dates for Hillsboro, Oregon
In Hillsboro, half of springs have had their last frost by April 16 (and 1 spring in 10 still has one after May 3), and half of falls have had their first frost by October 23, leaving about 191 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Hillsboro, Oregon
Last spring frost
April 16
Half of springs have their last frost by this date. For a safer bet, wait until May 3: only 1 spring in 10 has a frost after that.
First fall frost
October 23
Half of falls have their first frost by this date. In 1 fall in 10 it comes by October 3.
Growing season
191 days
Frost-free days in a typical year. 9 years in 10 get at least 161.
Hardiness zone
8b
2023 USDA map: the coldest night of winter averages 15°F to 20°F. It was 8b on the 2012 map too. ZIP codes within about 6 miles of the city's center: 6 in 8b and 1 in 9a.
Stations near you disagree. NOAA's Portland-Hillsboro Airport (1 mile away, at 200 feet above sea level), the one we used, gives a typical last frost of April 16 and a typical first frost of October 23. NOAA's Nature Park-Beaverton (5 miles away, at 180 feet above sea level) gives a typical last frost of February 11 and a typical first frost of December 5. So the typical last frost could fall anywhere from February 11 to April 16 and the typical first frost from October 23 to December 5, depending on whether your garden is more like one or the other. Local terrain matters: hillsides, valley floors, water and city heat can change frost dates a lot over a few miles. Treat the dates here as a starting point, and compare with a nearby gardener or your county extension office.
Print a year planner for Hillsboro
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | March 25 | April 16 | May 3 |
| First frost in fall | October 3 | October 23 | November 18 |
The frost-free season between them runs 191 days in a typical year. In 1 year in 10 it is 223 days or longer, and in 1 year in 10 it is 161 days or shorter.
- Hard freeze (28°F): typically last on March 13 and first on November 12. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on May 5 and first on October 6. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Hillsboro comes between March 25 and May 3, a window of 39 days. That is wider than at most NOAA stations (the typical window is 31 days), so spring here is less predictable than average: lean toward the later date.
Among Oregon's 162 NOAA stations with a frost every year, 59 percent have their typical last frost later than Hillsboro does.
Planting calendar for Hillsboro
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
| When | What to do | Why then |
|---|---|---|
| January | ||
| January 29 to February 26 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February | ||
| February 12 to March 12 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| February 26 to March 19 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March | ||
| March 5 to 19 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 12 to 26 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| March 19 to April 2 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| March 19 to April 2 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April | ||
| April 2 to 16 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 2 to 16 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| April 16 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| April 30 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| April 30 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| May | ||
| May 28 to June 11 | Cabbage for fall Start seeds | set the plants out by July 16 |
| June | ||
| June 17 to July 1 | Broccoli for fall Start seeds | set the plants out by August 5 |
| July | ||
| July 27 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 31 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 1 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 5 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| August 6 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 10 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August 20 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 30 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 9 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| October | ||
| October 3 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| November | ||
| November 19 to 26 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 17 days later. That plans around May 3, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Portland-Hillsboro Airport (station USW00094261), 1 mile from the center of Hillsboro. It sits at about the same elevation, 200 feet above sea level. NOAA rates this station's record as representative: at least 10 of the 30 years, with the gaps filled from nearby stations.
The same station also gives the frost dates for Beaverton and Cornelius.
Our ZIP code lookup matches these 3 ZIP codes to the same station, so they get the same dates: 97123, 97124, 97133. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Portland, Oregon: last frost around March 13, first frost around November 19 (15 miles away)
- Vancouver, Washington: last frost around March 29, first frost around November 9 (20 miles away)
- Gresham, Oregon: last frost around March 16, first frost around November 20 (25 miles away)
See frost dates across Oregon, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.