Portland OR Frost Dates — When to Plant & Protect Your Garden
Portland gardeners work with a 246-day frost-free growing season (noaa_frost_dates) in USDA zone 8b (usda_phzm_2023). The data below comes from NOAA weather station USW00024229, representing conditions across Portland’s ZIP codes 97201-97208 (hud_zip_crosswalk).
Your Last Spring Frost
Portland’s last spring frost dates show the probability of frost occurring after each date. Use the 80% confidence level for tender transplants, 50% for moderate risk tolerance.
| Confidence Level | Last Frost Date | Risk Profile |
|---|---|---|
| 90% confident | February 22 | Ultra-conservative |
| 80% confident | March 1 | Safe for tender plants |
| 70% confident | March 8 | Standard planning |
| 50% confident | March 16 | Moderate risk |
| 10% confident | April 6 | High risk |
Data source: NOAA Climate Normals 1991-2020 (noaa_frost_dates)
The 50% confidence date (March 16) represents the median last frost — half the years see frost after this date, half before.
Your First Fall Frost
Portland’s first fall frost probabilities help you plan harvest timing and protection strategies for late-season crops.
| Confidence Level | First Frost Date | Planning Use |
|---|---|---|
| 10% confident | October 26 | First possible frost |
| 50% confident | November 17 | Median first frost |
| 80% confident | December 1 | Conservative planning |
| 90% confident | December 8 | Very late frost |
Data source: NOAA Climate Normals 1991-2020 (noaa_frost_dates)
Your Growing Season
Portland’s frost-free season spans 246 days from the median last spring frost (March 16) to the median first fall frost (November 17) (noaa_frost_dates).
Monthly Growing Conditions
Portland’s climate data shows distinct seasonal patterns for garden planning:
| Month | Avg Temp | Avg High | Avg Low | Precipitation | Growing Degree Days |
|---|---|---|---|---|---|
| March | 48.2°F | 56.7°F | 39.6°F | 3.68” | 34 |
| April | 52.3°F | 61.4°F | 43.1°F | 2.73” | 100 |
| May | 58.3°F | 68.0°F | 48.6°F | 2.47” | 261 |
| June | 63.6°F | 73.5°F | 53.6°F | 1.70” | 407 |
| July | 69.2°F | 80.6°F | 57.8°F | 0.65” | 595 |
| August | 69.5°F | 81.1°F | 58.0°F | 0.67” | 606 |
| September | 64.5°F | 75.8°F | 53.1°F | 1.47” | 433 |
| October | 54.9°F | 63.8°F | 46.0°F | 3.00” | 168 |
Data source: NOAA Climate Normals 1991-2020 (noaa_cdo_historical)
Growing degree days accumulate rapidly from May through August, with peak accumulation in July (595) and August (606).
What This Means for Your Garden
Zone 8b Characteristics
Portland sits in USDA hardiness zone 8b, with minimum winter temperatures between 15°F and 20°F (usda_phzm_2023). This zone supports a wide range of perennial plants and allows for year-round growing of cool-season crops.
Chill Hour Accumulation
Zone 8b typically receives 350-600 chill hours annually, with 500 hours being typical (zone_chill_estimates). This supports most temperate fruit trees and berry crops.
This Week in Portland
Current Conditions (as of April 2, 2026 at 3:00 PM):
- Temperature: 53.2°F
- Humidity: 59%
- Wind: 9.6 mph
- Soil temperature (6”): 53.1°F
7-Day Forecast:
| Date | High | Low | Precip Chance | Frost Risk |
|---|---|---|---|---|
| Apr 2 | 53°F | 41°F | 52% | No |
| Apr 3 | 57°F | 38°F | 7% | No |
| Apr 4 | 67°F | 42°F | 1% | No |
| Apr 5 | 74°F | 46°F | 1% | No |
| Apr 6 | 74°F | 52°F | 3% | No |
| Apr 7 | 59°F | 44°F | 11% | No |
| Apr 8 | 61°F | 40°F | 10% | No |
Data source: Open-Meteo Forecast API (open_meteo_forecast)
No frost risk is forecast for the next seven days. April 6 matches the 10% confidence last frost date historically.
Your Growing Season: How’s It Going?
Spring Growing Degree Day Accumulation
Based on monthly normals, Portland accumulates growing degree days (base 50°F) as follows:
- March: 34 GDD
- April: 100 GDD
- May: 261 GDD
Peak accumulation occurs during summer months, with July and August each contributing over 595 growing degree days (noaa_cdo_historical).
About This Data
This page uses cross-referenced government data to provide location-specific frost dates for Portland, Oregon.
Primary Data Sources:
- Frost dates: NOAA Climate Normals 1991-2020, station USW00024229 (noaa_frost_dates)
- Hardiness zone: USDA Plant Hardiness Zone Map 2023 (usda_phzm_2023)
- Geographic coverage: HUD ZIP-USPS Crosswalk Q1 2024 for ZIP codes 97201-97208 (hud_zip_crosswalk)
- Climate data: NOAA CDO Climate Normals 1991-2020 (noaa_cdo_historical)
- Current forecast: Open-Meteo Forecast API (open_meteo_forecast)
- Demographics: Census ACS 5-Year 2022 (census_acs_5yr)
- Plant data: USDA PLANTS Database 2026-Q1 (usda_plants)
Geographic Coverage: Multnomah County, Oregon, specifically Portland ZIP codes 97201-97208, representing 808,098 residents (census_acs_5yr).
Station Details: NOAA weather station USW00024229 provides the 30-year climate normals used for frost date calculations. All frost probabilities represent historical frequencies from 1991-2020.
Data Vintage: Frost dates and climate normals reflect the official 1991-2020 averaging period. Forecast data updates hourly.
Frost Date Planner Calculator
Interactive planting date calculator coming soon. Will use pre-computed frost probability data to recommend optimal planting windows for your specific crops.
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