When to Apply Pre-Emergent: Soil Temperature and Dates Where You Live

Apply a crabgrass pre-emergent in spring when the top two inches of soil stay around 50–55°F for several days, just before crabgrass starts to germinate. In a normal year that is about mid-March in Philadelphia, St. Louis and Washington, late March or early April in Columbus, Indianapolis and Chicago, and mid- to late April in Detroit, Madison and Minneapolis. In the South, apply between mid-February and mid-March, and again in late summer or fall for winter weeds.

Below are typical dates for 22 cities, estimated from NOAA climate normals with Michigan State University’s crabgrass model and checked against Purdue, Penn State, Illinois and Nebraska.

The trigger is soil temperature, not the calendar

A pre-emergent does not kill weeds you can see; it stops seedlings as they sprout,¹¹ so it must be down before crabgrass germinates. Germination follows soil warmth, so extension services time the job by soil temperature.

Sources: Michigan State,² Nebraska,⁸ Texas A&M,¹¹ NC State,⁹ Penn State⁶ and Illinois.⁷

Why some say 50°F and others say 55°F

They describe two different moments. Michigan State’s 50–55°F is when to apply, leaving time to water the product in; the 55°F-and-up figures from Penn State, NC State and Illinois mark crabgrass already starting to sprout. They also measure at different depths and over different spans. Apply when the top two inches reach about 50°F and are still rising, and you are ahead of every threshold above.

To measure it, push a soil thermometer (or a meat thermometer that reads low enough) into the top inch of soil and check it several days running.¹¹

Typical pre-emergent dates for 22 northern cities

Our NOAA normals cover air temperature, not soil, so we used Michigan State University’s method. Its GDDTracker counts growing degree days (GDD) from February 15 with a base of 32°F, and its crabgrass model treats 250–500 GDD as the best application window, the stretch when the top two inches of soil typically reach 50–55°F.³ We ran that rule on NOAA’s 1991–2020 temperature normals for the station nearest each ZIP code.¹ Not sure whether your lawn is cool- or warm-season? See our guide to cool-season vs. warm-season grass.

“Germination begins” is the start of Michigan State’s crabgrass germination timer (200 GDD, base 50°F), its cue to scout for seedlings.³ Your window can differ by a week or more on a warm slope, in a frost pocket or far from the station.

How we estimated these dates

For each day we took the normal daily mean temperature (interpolated between NOAA’s monthly normals), subtracted 32°F and added up the positive values from February 15, GDDTracker’s simple-average method.³ The window opens when the total passes 250 and closes at 500. Michigan State stresses:

the GDD models are meant to serve as guides, not absolutes.

One limitation: a day below 32°F counts as zero, never negative, so a real spring with warm spells gains degree days faster than an average curve. In 2025 and 2026, Michigan State reported East Lansing at over 300 GDD by March 29;² our normal-year curve reaches 250 only on April 13. Treat the table as a planning date, then confirm with that year’s soil temperature, a live GDD tracker or the forsythia.

Do the dates match extension advice?

We compared our windows with dates that extension programs publish for their states:

Sources: Purdue’s preemergence timing note,⁴ Penn State’s crabgrass guidance,⁶ Illinois Extension⁷ and Nebraska Extension.⁸ Purdue and Penn State line up with our dates. Illinois and Nebraska wait closer to germination: Nebraska notes the product starts breaking down once applied, so going early shortens its useful life,⁸ and Illinois delays to the end of its window in a cold spring.⁷ Purdue leans the other way, because these herbicides break down very slowly in cool soil:

it’s better to error on the side of being early than too late.

If your state extension service publishes a window, use it; if not, ours is a reasonable middle.

Use the forsythia, and watch the sidewalk edges

Penn State calls forsythia in full bloom a good indicator, though it can bloom early or late in some years.⁶ Purdue calls it the “traditional” timing,⁵ and Michigan State finds its GDD window matches forsythia bloom in many years, but not always: in March 2026 bloom seemed to lag the model.²

Purdue points to “hotspots” along walks as the first places crabgrass may germinate,⁵ so treat strips beside driveways and sidewalks early in your window.

Southern lawns: earlier in spring, plus a fall application

Winter annuals such as annual bluegrass (Poa annua), chickweed and henbit sprout in late summer and fall, so UGA Extension¹⁰ and Texas A&M¹¹ recommend two applications a year. Michigan State’s model was built for the Midwest and Northeast, so for the South we list published windows:

NC State’s Fred Yelverton moved his advice earlier around 2020 after finding crabgrass germinating in North Carolina in February in four of five recent years.⁹ Our model gives Raleigh March 4–18, later than that advice, so use the published dates in the South. Texas A&M says timing there varies by several weeks by region.¹¹

In the North, a fall application clashes with early-fall seeding, the best time to thicken a cool-season lawn. Our guide on when to overseed your lawn has the last safe seeding day for your area.

Split applications and how long protection lasts

Crabgrass keeps germinating into summer, after the first barrier wears thin. Nebraska Extension recommends a second application, as the label directs, about mid-June for season-long control. White grubs need different products on a different calendar; see when to apply grub control.⁸ Penn State says some products may need a second application within 60 days,⁶ and UGA Extension says a second application 8 to 10 weeks after the first is permitted for some products.¹⁰ The label decides whether you can split, and how much goes into each application.

Pre-emergent and grass seed do not mix

Illinois Extension notes that, except for siduron, preemergence crabgrass products also damage germinating grass seed.⁷ Penn State advises waiting the time on the label before seeding, usually three to four months,⁶ and Nebraska Extension calls siduron (Tupersan) the only homeowner option for new seedings.⁸ Mesotrione (Tenacity) is also labeled at seeding for tolerant grasses, per the Pacific Northwest Weed Management Handbook.¹³

So seed in early fall and skip the fall pre-emergent, or treat in spring and seed in fall; to seed in spring, use a product labeled for seeding. See the seeding section.

Read the label first

Pre-emergents are pesticides, and the label sets how, how much and how often you may use them. As the US Environmental Protection Agency puts it:

In other words, the label is the law.

• Water it in. Michigan State’s window leaves time to water the product in before germination;² Texas A&M warns benefin can be lost if not watered in.¹¹
• Count weed-and-feed products. Many already contain a pre-emergent, so adding another can over-apply it.¹¹ Illinois does not recommend early spring fertilizing;⁷ see when to fertilize your lawn.
• Healthy turf only. Texas A&M advises against use on lawns under moderate to severe stress.¹¹

Missed the window?

Nebraska Extension says prodiamine and pendimethalin control one-leaf crabgrass if watered in right away, and dithiopyr at the full label rate kills seedlings before they tiller.⁸ Once most seedlings are up (80% germinate at 60–70°F soil, says Michigan State²), wait for next spring.

The cheapest fix is mowing height. In Nebraska turf research, raising the mowing height of Kentucky bluegrass from 1.5 to 2.5 inches cut crabgrass infestation from 80% to under 15%.⁸ Our mowing and watering guides explain the rest.

Related guideWhen to Overseed Your Lawn: The Last Safe Day Where You Live

Your next step

Put your window-open date in your calendar, then check the soil or the forsythia. Find your ZIP code’s spring frost dates with our frost date lookup, browse the weed control guides and other lawn care guides, or read our methodology.