Des Moines
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 5 – Oct 27
Iowa Weed Watch · updated Nov 3, 1:18 AM CT
When to apply pre-emergent in Iowa
Live soil temperatures for Des Moines, Cedar Rapids, Davenport and Sioux City, updated every three hours. Weeds sprout by soil temperature, not by the calendar, so the right week moves from year to year.
In Iowa, 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 Apr 9 – Apr 27
Stops crabgrass and other summer weeds before they sprout.
Fall: no pre-emergentThis season
Treat broadleaf weeds Sep 2 – Oct 28
Fall is seeding season here, and pre-emergent would stop grass seed too.
Right now · fall (seeding season)
Treat broadleaf weeds now across Iowa
Soil is 57–59°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.
Cedar Rapids
Treat broadleaf57°F↓ cooling
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 3 – Oct 27
Davenport
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 4 – Oct 28
Sioux City
Treat broadleaf57°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 22
Iowa 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 Iowa 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) |
|---|---|---|
| Des Moines | Apr 17 – Apr 20 | None (seeding season) · treat broadleaf Sep 5 – Oct 27 |
| Cedar Rapids | Apr 18 – Apr 22 | None (seeding season) · treat broadleaf Sep 3 – Oct 27 |
| Davenport | Apr 9 – Apr 20 | None (seeding season) · treat broadleaf Sep 4 – Oct 28 |
| Sioux City | Apr 16 – Apr 27 | None (seeding season) · treat broadleaf Sep 2 – Oct 22 |
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 Iowa are identifying
We record the state each identification comes from. Iowa'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 Iowa this fall
Questions about Iowa
When should I apply crabgrass pre-emergent in Iowa?
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 17 – Apr 20 in Des Moines; Apr 18 – Apr 22 in Cedar Rapids; Apr 9 – Apr 20 in Davenport; Apr 16 – Apr 27 in Sioux City.
Should I put down pre-emergent in the fall in Iowa?
Usually not. Fall is the best time to seed a cool-season lawn in Iowa, 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 Iowa right now?
As of Nov 3, 1:18 AM CT: Des Moines 59°F, Cedar Rapids 57°F, Davenport 58°F, Sioux City 57°F (5-day average, about 2.4 inches down). Treat broadleaf weeds now across Iowa.
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.