The short answer: The best time to apply weed killer depends on the type of product you’re using. Pre-emergent herbicides (which prevent weeds) 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 (which kill existing weeds) work best when weeds are young and actively growing, in moderate temperatures between 50 and 85°F. If you missed your pre-emergent window, don’t panic—you’ll need to switch to a post-emergent strategy and treat weeds as they appear, then get back on track with pre-emergent next season. It’s not ideal, but it’s not a disaster either. At Complete Lawn Care, our agronomy-supported program times applications based on soil temperature data and proven agronomic science—not guesswork or generic calendar dates.
Understanding the Two Types of Weed Control
Before we talk about timing, you need to understand that “weed killer” isn’t one thing—it’s two completely different approaches:
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. This is critical to understand—weed seeds don’t check the calendar before germinating. They respond to soil conditions.
Spring Pre-Emergent (for crabgrass and summer annual weeds)
Apply when soil temperatures reach 55°F at a 4-inch depth for several consecutive days. In the Tulsa metro area (including Jenks and Bixby), this typically occurs from late February to early March—but it varies year to year based on weather patterns. Too early: The product may break down before peak germination occurs. Too late: Crabgrass and other summer annuals have already sprouted, and pre-emergent won’t affect them.
A second application 6-8 weeks later extends the barrier through late spring, which is especially important for properties with heavy crabgrass pressure.
Fall Pre-Emergent (for winter annual weeds)
Apply in September before soil temperatures drop and trigger germination of winter annuals like henbit, chickweed, and annual bluegrass. These weeds germinate in fall, grow through winter (when your warm-season grass is dormant and can’t compete), and become highly visible in early spring. Fall pre-emergent is often overlooked but makes a huge difference in how your lawn looks come March.
Application
Timing
What It Prevents
Spring Pre-Emergent #1
Late Feb to Early Mar
Crabgrass, goosegrass, foxtail, spurge, and other summer annual weeds
Spring Pre-Emergent #2
Mid-April to Early May
Extends barrier for late-germinating summer weeds; recommended for high-pressure lawns
Fall Pre-Emergent
September
Henbit, chickweed, annual bluegrass (poa annua), and other winter annual weeds
When to Apply Post-Emergent Weed Killer
Post-emergent herbicides kill weeds that are already growing. For best results:
Target young, actively growing 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. When it’s too cold, weeds aren’t actively growing and won’t absorb the product effectively. When it’s too hot (above 85-90°F), herbicides can stress your lawn and may volatilize (evaporate) 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.
Don’t mow immediately before or after. Wait 2-3 days before mowing after application so the product has time to work. Mowing right before removes leaf surface area where the herbicide is absorbed.
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 designed for sedges. Using the wrong product wastes time and money.
What If I Missed My Pre-Emergent Application?
It happens. Life gets busy, you didn’t realize the timing window, or you just moved into a new house in Bixby and the previous owner didn’t treat the lawn. Here’s what to do:
First, 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 a post-emergent strategy.
You’ll need to 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.
Be aggressive early in the season.
Killing weeds before they produce seeds prevents them from creating next year’s problem. A single crabgrass plant can produce 150,000+ seeds. Every weed you kill before it seeds is thousands fewer weeds next spring.
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.
Get back on track next year.
Mark your calendar now: late February for spring pre-emergent. Set a reminder. Missing one year is frustrating but recoverable. Missing multiple years in a row creates a compounding weed seed bank problem that takes years to overcome.
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.
Applying post-emergent to mature weeds and expecting instant results. Large, established weeds may need multiple treatments. Be patient and retreat as needed.
Using the wrong product for the weed type. 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. More is not better. Excess herbicide can damage your lawn without killing weeds any faster. Follow label rates.
Expecting one application to solve 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 applications.
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.
That’s why we invest heavily in leadership training, research and development, and product testing, ensuring our team stays current on the latest turf products, application methods, and correction strategies. We’ve also implemented one of the few agronomy-supported programs in Tulsa, working directly with an industry expert who helps guide our application timing, product selection, and ongoing improvements based on proven agronomic science—not trends.
When it comes to weed control timing, this matters. We don’t just look at the calendar and say, “It’s March, time for pre-emergent.” 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.
Every lawn is different, and every application is intentional. At Complete Lawn Care, we don’t guess at what might work—we apply what does work.
The Bottom Line
Pre-emergent timing is based on soil temperature: late February to early March for spring weeds (when soil hits 55°F) and September for winter weeds.
Post-emergent works best on young weeds in moderate temperatures (50-85°F), with no rain expected for 24-48 hours.
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.
Year-round weed control is a process, not an event. Consistent, properly timed applications—combined with healthy turf—produce the best long-term results.
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. We also offer soil testing to identify underlying issues affecting turf health, because the best weed control is a thick, healthy lawn that crowds weeds out naturally.
Phone: (918) 605-4646
Email: [email protected]
Online: completelawncaretulsa.com/get-a-quote
Proudly serving Jenks, Bixby, Tulsa, Broken Arrow, Owasso, Sand Springs, and surrounding Oklahoma communities since 2000.