When Is the Best Time to Apply Weed Killer?
Pre-emergent herbicides should go down in late February to early March for spring weeds and in September for winter weeds—timed to soil temperature, not the calendar. Post-emergent herbicides work best when weeds are young and actively growing, in moderate temperatures between 50 and 85°F.
Understanding the Two Types of Weed Control
"Weed killer" isn't one thing—it's two completely different approaches. Knowing the difference is the foundation of effective weed management.
Pre-Emergent Herbicides (Prevention)
These create a chemical barrier in the top layer of soil that prevents weed seeds from germinating. They don't kill existing weeds—they stop new ones from sprouting. Think of it like a shield. Pre-emergents must be applied BEFORE weeds emerge from the soil. Once you see the weed, pre-emergent won't help with that plant. This is the most effective form of weed control because it addresses the problem before it's visible.
Post-Emergent Herbicides (Treatment)
These kill weeds that are already growing. They're absorbed through the leaves and work their way through the plant's system. Post-emergents are reactive—you're treating a problem that's already visible. They work, but it's always harder to kill a weed than to prevent it from growing in the first place.
When to Apply Pre-Emergent in Jenks, Bixby, and the Tulsa Area
Pre-emergent timing is based on soil temperature, not calendar dates. Weed seeds don't check the calendar before germinating—they respond to soil conditions.
Spring Pre-Emergent #1
Late Feb to Early Mar
Apply when soil temperatures reach 55°F at a 4-inch depth for several consecutive days. Prevents crabgrass, goosegrass, foxtail, spurge, and other summer annual weeds. Too early and the product breaks down before peak germination; too late and weeds have already sprouted.
Spring Pre-Emergent #2
Mid-April to Early May
A second application 6–8 weeks later extends the barrier through late spring. Especially important for properties with heavy crabgrass pressure. Targets late-germinating summer annual weeds.
Fall Pre-Emergent
September
Apply before soil temperatures drop and trigger germination of winter annuals like henbit, chickweed, and annual bluegrass. Often overlooked but makes a huge difference in how your lawn looks come March.
When to Apply Post-Emergent Weed Killer
Post-emergent herbicides kill weeds that are already growing. Follow these best practices for maximum effectiveness.
Target Young Weeds
Small weeds are much easier to kill than large, mature ones. A dandelion with two leaves is far more vulnerable than one with a deep taproot and a full rosette of leaves.
Apply in Moderate Temperatures
Most post-emergent herbicides work best between 50 and 85°F. Too cold and weeds won't absorb the product. Too hot (above 85–90°F) and herbicides can stress your lawn and volatilize before working.
Don't Apply Before Rain
Most post-emergents need 24–48 hours to be absorbed before rain or irrigation. Check the forecast before applying.
Match the Product to the Weed
Broadleaf herbicides kill dandelions and clover but won't touch grassy weeds. Crabgrass requires specific products. Nutsedge needs specialty herbicides. Using the wrong product wastes time and money.
What If I Missed My Pre-Emergent Application?
It happens. Here's how to recover and minimize the damage.
Don't Apply Pre-Emergent Anyway
If weeds have already germinated, pre-emergent won't kill them. You'd be wasting product and money. Pre-emergent only prevents germination—it doesn't affect plants that have already sprouted.
Switch to Post-Emergent Strategy
Treat weeds as they appear throughout the season. This is more work and less effective than prevention, but it's your best option now. Target weeds when they're young and small for best results.
Kill Weeds Before They Seed
A single crabgrass plant can produce 150,000+ seeds. Every weed you kill before it seeds is thousands fewer weeds next spring. Be aggressive early in the season.
Don't Skip Fall Pre-Emergent
Even if you missed spring, you can still prevent winter weeds by applying pre-emergent in September. This keeps henbit and chickweed from taking over your dormant Bermuda lawn.
Common Weed Killer Mistakes to Avoid
Applying Pre-Emergent Too Late
Once you see crabgrass, the pre-emergent window has passed. You need post-emergent now.
Wrong Product for the Weed
Broadleaf herbicides won't kill grassy weeds. Grassy weed killers won't kill broadleaf weeds. Nutsedge requires specialty products. Identification matters.
Applying in Extreme Heat
Herbicides applied above 85–90°F can damage your lawn and are less effective on weeds. Wait for a cooler day or apply in the early morning.
Over-Applying Herbicide
More is not better. Excess herbicide can damage your lawn without killing weeds any faster. Always follow label rates.
Expecting One Application to Fix Everything
Weed control is an ongoing process, not a one-time event. Different weeds germinate at different times throughout the year.
Ignoring the Underlying Problem
If you're constantly fighting weeds, the real issue is usually thin, unhealthy turf. Dense grass naturally crowds out weeds. Address mowing height, watering, fertilization, and soil health—not just herbicide.
Why Science-Based Timing Matters
For more than 25 years, Complete Lawn Care has been a trusted lawn care provider in the Tulsa area. We believe great results don't come from guessing—they come from experience, science, and continual improvement.
We've implemented one of the few agronomy-supported programs in Tulsa, working directly with an industry expert who guides our application timing, product selection, and ongoing improvements based on proven agronomic science—not trends. We monitor soil temperature data, evaluate weather patterns, and adjust our timing based on what's actually happening in Jenks, Bixby, and across the Tulsa metro. Experience tells us what to do. Science tells us when and why.
The Bottom Line
Pre-Emergent Timing
Based on soil temperature: late February to early March for spring weeds (when soil hits 55°F) and September for winter weeds.
Post-Emergent Best Practices
Works best on young weeds in moderate temperatures (50–85°F), with no rain expected for 24–48 hours after application.
If You Missed Pre-Emergent
Switch to post-emergent treatment and get back on track next season. Kill weeds before they seed to reduce next year's problem.
Weed Control Is a Process
Year-round, consistent, properly timed applications—combined with healthy turf—produce the best long-term results. It's never a one-time event.
Ready for Weed Control That's Timed Right?
Complete Lawn Care's 7-step program includes properly timed pre-emergent and post-emergent applications throughout the year. We monitor conditions, adjust timing based on agronomic data, and address breakthrough weeds between scheduled visits at no extra charge. Whether you're in Jenks, Bixby, or anywhere in the Tulsa metro, we can help you get ahead of weeds—or recover if you've fallen behind.
📞 (918) 605-4646 ✉ wecare@completelawncaretulsa.com
Proudly serving Jenks, Bixby, Tulsa, Broken Arrow, Owasso, Sand Springs, and surrounding Oklahoma communities since 2000.
