When to Apply Pre-Emergent Herbicide (Spring & Fall Guide)

Stop weeds before they start. Pre-emergent herbicide is your secret weapon for a weed-free lawn — but timing is everything. Apply too early or too late, and you’ve wasted your time and money.

The best time to apply pre-emergent is when soil temperature reaches 50-55 degrees F in spring and drops to 70 degrees F in fall. With tips from an expert, this guide shows you exactly when to apply pre-emergent herbicides based on your location and what weeds you’re fighting.

Too busy to time it perfectly? LawnStarter’s lawn treatment pros handle pre-emergent applications at exactly the right time for your lawn. We take weed prevention off your to-do list. Get a free lawn treatment quote.

Key Takeaways:  • Apply before weeds appear. Pre-emergents don’t kill existing weeds. • Apply in both spring and fall for year-round weed prevention. • Spring applications prevent summer weeds. • Fall applications prevent winter weeds.

When to Apply Pre-Emergent Herbicide

	Soil Temperature	Timing	Targets
Spring	50 to 55 degrees F	Late winter to early spring (before weeds sprout)	Crabgrass, foxtail, spurge
Fall	70 degrees F	Late summer to early fall	Common winter weeds: chickweed, henbit, annual bluegrass

Apply pre-emergent herbicides before you see weeds. Pre-emergents create a barrier in the soil that stops weed seeds from sprouting. Once weeds are visible, you need a post-emergent herbicide instead. 

What is Pre-Emergent Herbicide?

Pre-emergent herbicides prevent weeds from growing in your lawn by stopping seeds from germinating. Think of it as an invisible barrier just below the soil surface.

Pre-emergent weed preventers are best suited for grassy weeds and annual weeds that reproduce by seeds, says Rebecca Grubbs-Bowling, assistant professor and turfgrass Extension specialist at the University of Tennessee. “They don’t work as well on perennials.”

How it works:

• Stops weed roots and shoots from developing
• Must be applied before weeds appear
• Lasts 8-12 weeks (varies by product)
• Does not kill existing weeds

See Related: How to Apply Pre-Emergent Herbicide

Spring Pre-Emergent Application

When to apply in spring: “The soil temperature (not air temperature) should be in the 50-55 degree F range,” says Grubbs-Bowling. 

Many dormant seeds begin germinating once soil temperatures hit 55 degrees F. This is when summer annual weed seeds start germinating.

Here’s a guide for when to apply spring pre-emergents by region:

Region	Best Application Window	What You’re Preventing
Florida	Early February	Crabgrass, spurge
Texas	Early to mid February	Crabgrass, annual bluegrass, sandbur, foxtail
Mid-Atlantic (Virginia, North Carolina)	Mid-February to mid-March	Crabgrass, foxtail, goosegrass
Midwest (Missouri, Illinois)	Mid-March to mid-April	Crabgrass, foxtail, goosegrass
Northeast (Pennsylvania, Massachusetts)	Late March to early April	Crabgrass, foxtail, goosegrass
Wisconsin, Minnesota	Mid-April to mid-May	Crabgrass, foxtail
Colorado, Mountain states	Mid-March to mid-April	Crabgrass, foxtail, goosegrass

How to check soil temperature

Don’t guess — measure.

1. Use online soil temperature maps from your county Extension office or a local weather station.
2. Use a soil thermometer (cheap at garden stores). Push 3 inches into the soil. You can find inexpensive soil temperature gauges online or at local garden shops. You can also use a 3-inch meat thermometer.
3. Check for 3 consecutive days that the soil temperature is 50-55 degrees F before applying.

Common spring weeds prevented

• Crabgrass: The #1 grassy lawn weed; spreads rapidly in summer heat
• Dandelions: Yellow flowers that turn into puffballs
• Spurge: Mat-forming weed with reddish brown stems
• Ragweed: Fern-like weed that produces a large amount of pollen
• Sandbur: Painful, spiky seed heads
• Yellow foxtail: Bushy spike seed heads

See Related: 

• When and How to Apply Crabgrass Preventer
• How to Get Rid of Crabgrass in Your Yard
• How Dandelions Benefit You and Your Yard

Fall Pre-Emergent Application

When to apply in fall: Apply when soil temperature drops to 70 degrees F — this prevents winter annual weeds that germinate in fall.

Here’s a guide for when to apply fall pre-emergents by region:

Region	Best Application Window	What You’re Preventing
Florida	Mid-October to mid-November	Annual bluegrass, chickweed, henbit
Texas	Late September to October	Annual bluegrass, chickweed, henbit, rescuegrass
Mid-Atlantic (Virginia, North Carolina)	August to September	Annual bluegrass, chickweed, henbit
Midwest (Missouri, Illinois)	September	Chickweed, henbit
Northeast	September	Chickweed, henbit

Common fall/winter weeds prevented:

• Annual bluegrass: Light green, grows in cool weather
• Cheatgrass: Light green stems with feathery tips
• Chickweed: Small white flowers, thrives in shade
• Henbit: Purple tubular flowers, scalloped leaves
• Persian speedwell: Delicate blue flowers

Why fall matters: Winter annuals usually germinate in the fall, overwinter as small plants, then proliferate as temperatures warm up in the spring.

See Related:

• How to Get Rid of Cheatgrass
• Read Your Weeds: Identify Them to Learn About Your Lawn’s Health

Weeds Needing Both Spring and Fall Applications

Some weeds are tricky — they can germinate in either season:

• Clover can be either a summer or winter annual. Apply pre-emergents in both spring and fall to treat this weed. Many homeowners now embrace clover for its benefits, as it is nitrogen-rich and pollinator-friendly. Learn about reasons to plant a clover lawn.
• Spurge, a broadleaf weed, can be easily identified by its red hairy stem and dense mat of dark green leaves close to the ground. Various species germinate at different times. Treat in both seasons for full control.

When Pre-Emergent Doesn’t Work

Pre-emergents fail when:

• Applied too late: Weeds have already germinated
• Soil is disturbed: Aeration, dethatching, or digging breaks the barrier
• Not watered in properly: Pre-emergents need water to activate
• The wrong product is applied: Some pre-emergents don’t target all weeds

See Related:

• What is Core Aeration?
• Applying Post-Emergent Herbicides to Your Lawn

FAQ About Pre-Emergents

Let LawnStarter Handle Weed Prevention

Timing pre-emergent applications perfectly means monitoring soil temperatures, watching weather patterns, and applying at exactly the right moment. Miss the window by a few weeks, and weeds take over.

LawnStarter’s lawn treatment pros:

• Apply pre-emergent at optimal timing
• Use professional-grade products
• Include weed control in comprehensive lawn care plans
• Guarantee results

Get a free quote for lawn treatment →

We’ll keep weeds out of your lawn so you can enjoy it instead of fighting it.

Main Image: Lawn fertilizer spreader positioned on pavement beside grass. Image Credit: WH_Pics / Adobe Stock