Fall Pre-Emergent

Apply fall pre-emergent in early September to block poa annua and winter weeds.

Fall is one of the most important times to apply pre-emergent herbicides—especially for warm-season lawns. As soil temperatures drop in late summer and early fall, weed seeds like poa annua, chickweed, and other winter annuals begin to germinate. Applying a fall pre-emergent creates a barrier that stops these weeds before they sprout, keeping your lawn clean and healthy through winter and spring.

When to Apply Fall Pre-Emergent

The best time to apply fall pre-emergent is in early September when soil temperatures are between 70–75°F and beginning to cool. This is the window when poa annua (annual bluegrass) and other broadleaf weed seeds start to germinate. Applying pre-emergent at the right time blocks these weeds before they ever become visible in your lawn.

Important: Do Not Use Pre-Emergent If Overseeding Cool-Season Grass

If you're overseeding in the fall, do not use pre-emergent. These products form a barrier in the soil that will prevent all seeds from germinating—including your grass seed. Wait until after new grass is established (typically 4-6 weeks) before using any weed control products.

Best Pre-Emergent for Fall Lawns

We recommend Guardian™ 13-0-10 with Prodiamine for fall pre-emergent control. It's ideal for warm-season lawns like Bermuda and Zoysia that are not being overseeded. Guardian contains:

  • Prodiamine: Trusted pre-emergent active that blocks weed seed germination
  • 13% Nitrogen: Encourages strong, green growth while temperatures are still warm
  • 10% Potassium: Improves disease resistance and root strength heading into winter

This dual-purpose formula feeds your lawn while protecting it—making it a smart and efficient fall application.

How to Apply

  • Apply with a broadcast spreader at 5 lbs. per 1,000 sq. ft. rate
  • Water in with at least ½ inch of irrigation within 48 hours
  • Do not aerate or disturb the soil after application

Ideal For:

  • Warm-season lawns (Bermuda, Zoysia, St. Augustine)
  • Homeowners who are not overseeding in fall
  • Blocking poa annua, chickweed, henbit, and other winter weeds

Got Questions?

Frequently Asked.

Everything you need to know before you start your daily routine.

What is the best time to apply fall pre-emergent?

Early September, when soil temps begin to cool to around 70°F. This targets the germination window of poa annua and other winter weeds.

Can I apply pre-emergent if I’m overseeding in fall?

No. Pre-emergents will prevent your grass seed from germinating. If you’re seeding tall fescue or bluegrass, skip pre-emergent and focus on lawn establishment first.

What’s the best fall pre-emergent for warm-season lawns?

Guardian™ 13-0-10 is ideal. It contains prodiamine for weed control, plus nitrogen and potassium to strengthen your lawn before winter dormancy.

Will pre-emergent kill existing weeds?

No. Pre-emergents stop new weed seeds from germinating but do not kill established weeds. Spot-spray existing weeds with post-emergent herbicides instead.

Do I need to water in pre-emergent?

Yes. Water with at least ½ inch of irrigation within 1–2 days of application to activate the barrier in the soil.