When is the last frost in Hillsboro, OR?

The average last spring frost (50% probability of 32°F) in Hillsboro is around April 16, based on NOAA/NCEI 1991–2020 normals at the Portland-hillsboro Ap, OR station (6.8 mi away). Half of years it falls outside that date, so wait 1–2 weeks past it before setting out frost-tender plants.

When is the first fall frost in Hillsboro?

The average first fall frost in Hillsboro, OR is around October 23, giving roughly a 191-day frost-free growing season.

What planting zone is Hillsboro, OR?

Hillsboro is in USDA plant hardiness zone 8b (average annual extreme minimum temperature 15 to 20°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in Hillsboro?

In Hillsboro, OR the warmest month is August (avg high 82.2°F) and the coldest is January (avg low 32.6°F). It averages about 46.7″ of precipitation a year and 2.7″ of snow.

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Hillsboro, OR Planting Calendar & Frost Dates

USDA hardiness zone 8b · ZIP 97123 · elevation 55′ · NOAA & USDA data

Hillsboro is in USDA hardiness zone 8b (winters can dip to 15 to 20°F), with a growing season of about 191 days between the average last spring frost (April 16) and first fall frost (October 23). The warmest month is August (avg high 82.2°F); the coldest is January (avg low 32.6°F). It averages 46.7″ of precipitation a year and 2.7″ of snow, mostly mid-winter. Start cool-season crops several weeks before the last frost; wait until after it for tomatoes, peppers and other tender crops.

Hardiness zone

min temp 15 to 20°F

Last spring frost

April 16

avg (50% prob, 32°F)

First fall frost

October 23

avg (50% prob, 32°F)

Growing season

191 days

frost-free window

Warmest month

August

avg high 82.2°F

Month-by-month typical weather in Hillsboro

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Forest Grove, OR (8.3 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	45	32.6	38.8	7.2	0.6
February	49.4	33.1	41.2	5.8	0.6
March	54.6	35.9	45.2	5	0
April	60.1	39.2	49.6	3.3	0
May	68.1	45.3	56.7	2.2	0
June	73.1	49.7	61.4	1.4	0
July	81.4	53.8	67.6	0.3	0
August	82.2	53.5	67.9	0.5	0
September	76.1	48.7	62.4	1.3	0
October	63.3	41.6	52.4	3.7	0.2
November	50.9	36.3	43.6	7.2	0
December	44	32.8	38.4	8.7	1.3

What to plant when in Hillsboro

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: March 5 · Transplant out: April 23
Peppers	warm	Start seeds indoors: February 19 · Transplant out: April 30
Cucumbers	warm	Direct sow: April 23
Zucchini / squash	warm	Direct sow: April 23
Bush beans	warm	Direct sow: April 23
Sweet corn	warm	Direct sow: April 23
Basil	warm	Transplant out: April 23
Peas	cool	Sow (spring): March 12 · Sow (fall): August 28
Spinach	cool	Sow (spring): March 5 · Sow (fall): August 28
Lettuce	cool	Sow (spring): March 19 · Sow (fall): August 28
Kale	cool	Transplant (spring): March 26 · Sow (fall): August 14
Broccoli	cool	Transplant (spring): April 2
Carrots	cool	Sow (spring): March 26 · Sow (fall): August 14
Onions	cool	Transplant (spring): March 19
Potatoes	cool	Plant seed potatoes: April 2
Radishes	cool	Sow (spring): March 19 · Sow (fall): September 11

Dates are computed from Hillsboro's average frost dates using standard cool-/warm-season timing. They're a starting point — a cold spring, a warm microclimate, or a fast-maturing variety can shift them by a week or two.

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Gear that helps you plant on time

Some links below are Amazon affiliate links (tag theboringthin-20). If you buy through them we may earn a small commission at no extra cost to you — it keeps this almanac free. We only list generic, genuinely-useful categories.

Soil thermometer →Know when the ground is warm enough to sow — the honest signal, not the calendar.Seed-starting trays + dome →Start tomatoes & peppers indoors on the schedule below.Seedling heat mat →Warms the soil for faster, more even germination indoors.Floating row cover / frost cloth →Buys you 4–8°F to beat an early or late frost.Raised garden bed kit →Warms and drains faster in spring than in-ground soil.Garden gloves →Basic kit for transplant day.

Nearby cities in Oregon

Beaverton, OR Lake Oswego, OR Portland, OR Gresham, OR Salem, OR Albany, OR Corvallis, OR Eugene, OR

Sources & method. Hardiness zone: 2023 USDA Plant Hardiness Zone Map (PRISM Climate Group, Oregon State University). Frost dates & growing season: NOAA/NCEI 1991–2020 U.S. Climate Normals, nearest station with published freeze normals — Portland-hillsboro Ap, OR, 6.8 mi (confidence: high). Monthly weather normals: Forest Grove, OR, 8.3 mi (confidence: high). ZIP centroid from U.S. Census 2023 ZCTA data. Frost dates are the 50%-probability date — half of years frost occurs outside the stated date. Nothing here is invented; where the nearest station is far, we say so. Last updated 2026-07-22.