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

Frequently Asked Questions

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.

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