Chicago
Treat broadleaf58°F↓ cooling
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 10 – Nov 7
Illinois Weed Watch · updated Nov 3, 1:18 AM CT
When to apply pre-emergent in Illinois
Live soil temperatures for Chicago, Peoria, Springfield and Carbondale, updated every three hours. Weeds sprout by soil temperature, not by the calendar, so the right week moves from year to year.
In Illinois, pre-emergent is a spring job: it stops crabgrass. Fall is seeding season here, so fall weed control means treating broadleaf weeds instead.
Spring pre-emergentNext season
Typically Mar 15 – Apr 24
Stops crabgrass and other summer weeds before they sprout.
Fall: no pre-emergentThis season
Treat broadleaf weeds Sep 1 – Nov 7
Fall is seeding season here, and pre-emergent would stop grass seed too.
Right now · fall (seeding season)
Treat broadleaf weeds now across Illinois
Soil is 58–62°F now. In fall, dandelions, clover and creeping Charlie pull sugars — and weed killer — down to their roots. Seeding this fall? Skip pre-emergent; it stops grass seed too.
Soil temperature by city
Soil 2 inches down, 5-day average: solid line = the last two weeks, dashed = the six-day forecast.
Peoria
Treat broadleaf59°F↓ cooling
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 1 – Oct 31
Springfield
Treat broadleaf60°F↓ cooling
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 4 – Oct 31
Carbondale
Treat broadleaf62°F↓ cooling
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 2 – Oct 31
Illinois pre-emergent calendar
Spring pre-emergent stops crabgrass. The window runs from the typical day soil warms to 50°F to the day it holds 55°F, when crabgrass starts germinating (2016–2025). In fall Illinois lawns are in seeding season, so there is no fall pre-emergent; the window shown is for treating broadleaf weeds instead, from September until two weeks after soil usually cools to 55°F.
| City | Spring pre-emergent (crabgrass) | Fall (seeding season) |
|---|---|---|
| Chicago | Apr 14 – Apr 24 | None (seeding season) · treat broadleaf Sep 10 – Nov 7 |
| Peoria | Apr 3 – Apr 19 | None (seeding season) · treat broadleaf Sep 1 – Oct 31 |
| Springfield | Mar 29 – Apr 15 | None (seeding season) · treat broadleaf Sep 4 – Oct 31 |
| Carbondale | Mar 15 – Apr 7 | None (seeding season) · treat broadleaf Sep 2 – Oct 31 |
These are typical-year dates (the median of 2016–2025); any one year can run a couple of weeks earlier or later, which is what the live readings above are for. For your exact yard, check soil temperature by ZIP.
What people in Illinois are identifying
We record the state each identification comes from. Illinois's list appears here once it has at least 40 identifications spread over 7 or more days — so no single scan stands out. Until then, see the national list, or add yours:
Identify a weed from a photoWeeds to watch in Illinois this fall
Questions about Illinois
When should I apply crabgrass pre-emergent in Illinois?
Put crabgrass pre-emergent down as soil warms to 50°F, before it holds 55°F and crabgrass starts germinating. In a typical year (2016–2025) that window is Apr 14 – Apr 24 in Chicago; Apr 3 – Apr 19 in Peoria; Mar 29 – Apr 15 in Springfield; Mar 15 – Apr 7 in Carbondale.
Should I put down pre-emergent in the fall in Illinois?
Usually not. Fall is the best time to seed a cool-season lawn in Illinois, and pre-emergent stops grass seed as well as weeds. Fall is the time to treat broadleaf weeds such as dandelion, clover and creeping Charlie, once the summer heat breaks and while they are still growing.
What is the soil temperature in Illinois right now?
As of Nov 3, 1:18 AM CT: Chicago 58°F, Peoria 59°F, Springfield 60°F, Carbondale 62°F (5-day average, about 2.4 inches down). Treat broadleaf weeds now across Illinois.
How the readings and dates are made, and their limits: Weed Watch method. Soil data: Open-Meteo.com (CC BY 4.0); typical dates: NASA POWER.