Best days to spray weeds in Portland, OR this week
Here's the next 7 days for spraying weeds in Portland, checked hour by hour against the published thresholds. Below it: what Portland's 1991–2020 climate averages say about the months that usually work.
This week in Portland
Asking the sky…
Fairsky is not a substitute for official warnings. For warnings, go to weather.gov. Verdicts are guidance, not guarantees. Your product's label always wins.
When spraying weeds usually works in Portland
- On 1991–2020 averages, Portland's normal highs fall inside Fairsky's 45–85°F spray band in every month of the year.
- January is the rainiest of the spray months, averaging 13.8 days with 0.10" or more; Fairsky wants 4 rain-free hours after spraying.
- Averages can't tell you about wind, and wind decides most spray days (3–10 mph is the target), so lean on the live verdict.
| Month | Avg high | Avg low | Days ≥0.10" rain | Highs 45–85°F |
|---|---|---|---|---|
| January | 47° | 37° | 13.8 | Yes |
| February | 51° | 39° | 10.3 | Yes |
| March | 56° | 41° | 12.1 | Yes |
| April | 61° | 44° | 10.5 | Yes |
| May | 68° | 49° | 7.5 | Yes |
| June | 73° | 53° | 4.9 | Yes |
| July | 80° | 58° | 1.5 | Yes |
| August | 81° | 59° | 1.6 | Yes |
| September | 75° | 55° | 4.1 | Yes |
| October | 63° | 48° | 8.5 | Yes |
| November | 52° | 42° | 13.4 | Yes |
| December | 46° | 37° | 13.8 | Yes |
Station: Portland Kgw-Tv (NOAA NCEI USC00356749), about 1 km from central Portland. “Rain days” count days with 0.10" or more of precipitation. “Highs 45–85°F” checks the monthly averages only; any given week can be warmer, colder or wetter.
The rules we check
- Needs 2 hours in a row of daylight.
- Air at least 45°F.
- No hotter than 85°F (86–90°F is borderline).
- Wind between 3 and 10 mph (calmer air can mean a temperature inversion that carries drift).
- Gusts at or under 15 mph. (Fairsky default: no source gave a number)
- Rain chance at or below 20%. (Fairsky default: no source gave a number)
- No rain for 4 hours after you finish.
Your product's label always wins. Labels differ by product; in the app you can enter your label's temperature range and rain-free hours, and the verdict uses them instead.
Sources: NC State Extension: spray drift and wind speed · UNL CropWatch: avoiding herbicide drift · UNL CropWatch: managing applications to avoid drift · Rutgers: herbicide drift and temperature · Roundup concentrate label (rainfast time)
More home and yard jobs in Portland
- Stain a deckDeck and fence stain: 50–90°F, dry wood, 24 rain-free hours after.
- Paint a house exteriorExterior latex paint: 40°F and up, 5°F above the dew point, 4 dry hours after.
- Pour concreteConcrete: 40–85°F, no rain for 24 hours, no freezing for 48.
- Apply pre-emergentCrabgrass pre-emergent: before soil holds 55°F (about 200 GDD), then water it in.
- Plant grass seedCool-season grass seed: soil about 50–65°F, highs 60–80°F, no washout rain.
- Seal a drivewayAsphalt sealcoat: 55°F and rising, 50°F overnight, 36 rain-free hours.
- Cover plants for frostFrost watch: cover at 34°F, or 36°F on clear, calm nights; 28°F is a hard freeze.
The app covers 47 activities in all, from mowing to a round of golf: see every activity and its rules.
Spray weeds in nearby cities
- Seattle, WA145 miles away
- Spokane, WA290 miles away
- Boise, ID345 miles away
- Sacramento, CA483 miles away
- Stockton, CA527 miles away
- San Francisco, CA535 miles away
All spray weeds cities: Spray weeds, by city · Home and yard in Oregon
Questions
What's the best month to spray weeds in Portland?
On 1991–2020 averages, July usually fits best in Portland. Any given week can still be wrong for it, which is what the live verdict above is for.
How is this verdict made?
We take the National Weather Service hourly forecast for Portland and check each hour against the thresholds listed above. The result is guidance, not a guarantee; your product's label always wins.
Is it too windy to spray weeds in Portland today?
Look for steady winds of about 3–10 mph with low gusts and no rain for a few hours after. The hourly verdict above shows when Portland gets there.
Fairsky is not a substitute for official warnings. For warnings, go to weather.gov.
Live forecasts: National Weather Service / NOAA (public domain), fetched by your browser. Climate averages: NOAA NCEI U.S. Climate Normals, 1991–2020 (public domain). Activity thresholds: product data sheets, ACI and university extension guidance, linked on each page; your product’s label wins.