In Oklahoma, apply spring pre-emergent herbicide in late February to early March, before soil temperatures consistently reach 55°F. This prevents crabgrass, foxtail, and other summer annual weeds from germinating. A second application in fall (September-October) prevents winter annual weeds like henbit and chickweed. Miss these windows and you’ll spend all season fighting weeds that could have been prevented.
Timing is everything with pre-emergent. Apply too early, and it breaks down before weeds germinate. Apply too late, and weeds have already sprouted right through your expensive barrier. At Complete Lawn Care, we monitor soil temperatures across the Tulsa area to nail this timing for our customers. Here’s how to get it right yourself.
What Is Pre-Emergent Herbicide, and How Does It Work?
Pre-emergent herbicide creates a chemical barrier in the top layer of soil that prevents weed seeds from germinating successfully. Think of it like birth control for weeds. It doesn’t kill existing weeds. It stops NEW weeds from ever getting started.
When a weed seed germinates, it sends out a tiny root and shoot. Pre-emergent herbicide interrupts this process, killing the seedling before it ever breaks the soil surface. The result? No crabgrass, no foxtail, no goosegrass, just your grass.
Key point: Pre-emergent only works on seeds that haven’t germinated yet. Once you see weeds, pre-emergent won’t help. You’ve missed the window and will need post-emergent herbicides to kill visible weeds.
What Is the 150 Rule for Pre-Emergent Timing?
You may have heard of the “150 rule” or “soil temperature rule” for pre-emergent timing. Here’s what it means:
Crabgrass and most summer annual weeds germinate when soil temperatures at 4 inches deep reach 55°F for several consecutive days. The old “150 rule” came from a method of tracking cumulative growing degree days, but the simpler approach is to apply pre-emergent before soil temperatures consistently hit 55°F.
In the Tulsa area, this typically happens:
• Late February to mid-March in most years
• A week or two earlier during warm winters
• A week or two later during cold springs
• When forsythia bushes start blooming (a traditional indicator)
Complete Lawn Care monitors actual soil temperatures across our service area rather than relying on calendar dates. Weather varies year to year, and we adjust our application timing accordingly.
Spring Pre-Emergent: Stopping Summer Weeds
What it prevents: Crabgrass, goosegrass, foxtail, spurge, and other summer annual weeds that germinate in spring and plague your lawn all summer.
When to apply: Late February to early March in the Tulsa area. You want the barrier in place BEFORE soil temps hit 55°F.
How long it lasts: Most pre-emergent products provide 8-12 weeks of protection. Some premium products last longer. This is usually enough to cover the primary crabgrass germination window.
Split application option: For extended protection, some lawn care programs split the pre-emergent into two applications, one in early spring and one in late spring. This extends the barrier through more of the summer weed germination period.
Fall Pre-Emergent: Preventing Winter Weeds
Many homeowners don’t realize that fall pre-emergent is just as important as spring. Winter annual weeds germinate in fall, survive winter, and then take over your lawn in early spring before your grass even wakes up.
What it prevents: Henbit, chickweed, annual bluegrass (Poa annua), and other winter annual weeds that make lawns look terrible in early spring.
When to apply: September to early October in Oklahoma, before soil temperatures drop below 70°F consistently. This puts the barrier in place before winter annual weed seeds germinate.
Bonus benefit: Fall pre-emergent also provides some continued protection against late-germinating summer weeds that might try to sneak in.
Common Pre-Emergent Mistakes
Applying too late: If you see crabgrass, you’re too late. Pre-emergent won’t help weeds that have already germinated. Many homeowners apply in April when they’re thinking about lawn care, but in Oklahoma, that’s often 4-6 weeks too late.
Not watering it in: Pre-emergent needs to be watered into the soil to create an effective barrier. Apply before rain, or water in with 1/2 inch of irrigation within 24-48 hours of application.
Disturbing the barrier: Heavy raking, dethatching, or aerating after pre-emergent application breaks up the barrier. If you need to aerate, do it BEFORE pre-emergent, not after.
Skipping fall application: Then wondering why henbit and chickweed take over in spring. Fall pre-emergent is just as important as spring.
Using pre-emergent when overseeding: Pre-emergent stops ALL seeds from germinating, including grass seed. If you’re overseeding fescue in fall, you cannot use pre-emergent in that same area. Choose one or the other.
Get Pre-Emergent Timing Right
Complete Lawn Care’s 7-step program includes properly timed pre-emergent applications in both spring and fall. We monitor soil temperatures across the Tulsa area and time applications based on actual conditions, not calendar dates. You get weed prevention that actually works because timing is dialed in for Oklahoma.
Call: (918) 605-4646
Email: [email protected]
Online: completelawncaretulsa.com/get-a-quote
Serving Tulsa, Broken Arrow, Bixby, Jenks, Owasso, Sand Springs, and surrounding communities.