Best days to spray weeds in Chicago, IL this week
Here's the next 7 days for spraying weeds in Chicago, checked hour by hour against the published thresholds. Below it: what Chicago's 1991–2020 climate averages say about the months that usually work.
This week in Chicago
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 Chicago
- On 1991–2020 averages, Chicago's normal highs fall inside Fairsky's 45–85°F spray band in March–November.
- In December–February, normal highs stay under 45°F, below the 45°F daytime minimum on common homeowner weed-killer labels.
- May is the rainiest of the spray months, averaging 8.2 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 | 33° | 19° | 3.4 | – |
| February | 37° | 23° | 3.4 | – |
| March | 48° | 32° | 5.0 | Yes |
| April | 60° | 41° | 6.9 | Yes |
| May | 71° | 52° | 8.2 | Yes |
| June | 81° | 62° | 8.0 | Yes |
| July | 85° | 68° | 5.5 | Yes |
| August | 83° | 66° | 6.4 | Yes |
| September | 76° | 59° | 5.4 | Yes |
| October | 63° | 47° | 6.3 | Yes |
| November | 49° | 35° | 4.7 | Yes |
| December | 38° | 25° | 4.3 | – |
Station: Chicago Midway Airport (NOAA NCEI USW00014819), about 14 km from central Chicago. “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 Chicago
- 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
- Milwaukee, WI81 miles away
- Madison, WI122 miles away
- Grand Rapids, MI125 miles away
- Indianapolis, IN165 miles away
- Toledo, OH211 miles away
- Dayton, OH232 miles away
All spray weeds cities: Spray weeds, by city · Home and yard in Illinois
Questions
What's the best month to spray weeds in Chicago?
On 1991–2020 averages, November usually fits best in Chicago. 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 Chicago 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 Chicago 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 Chicago 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.