Crabgrass Control Guide
Digitaria spp.
Crabgrass is the most common lawn weed in America, and for good reason—a single plant can produce up to 150,000 seeds. The good news? With the right timing and strategy, you can achieve 95%+ prevention. This guide covers everything from identification to elimination, with specific advice for your grass type and region.
At a Glance
How to Identify Crabgrass
Before treating, confirm you actually have crabgrass. It's often confused with other grassy weeds like quackgrass, dallisgrass, or tall fescue clumps.
Images: Wikimedia Commons (CC BY 2.5)
Key Identification Features
Growth Pattern
Grows flat and spreads outward in a star or crab-like pattern from a central point. Stems (tillers) radiate horizontally before turning upward.
Leaf Appearance
Wider blades than most lawn grasses (¼ to ⅓ inch wide). Light green to yellow-green color. Leaves have a distinct center fold and may appear hairy.
Seed Heads
Finger-like seed spikes (3-7 per stem) appear in mid to late summer, resembling a bird's foot. This is the "crab" in crabgrass.
Root Structure
Shallow, fibrous root system. Plants can root at nodes where stems touch the ground, helping it spread rapidly.
Crabgrass vs. Look-Alikes
| Feature | Crabgrass | Quackgrass | Tall Fescue Clumps |
|---|---|---|---|
| Type | Annual (dies in winter) | Perennial (survives winter) | Perennial |
| Growth | Low, spreading | Upright, aggressive | Upright bunches |
| Roots | Shallow, fibrous | Deep rhizomes | Deep, fibrous |
| Pre-emergent Works? | Yes | No | N/A (not a weed) |
Why Crabgrass Takes Over (The Lifecycle)
Understanding the crabgrass lifecycle reveals exactly when and how to attack it. Crabgrass is an annual weed, completing its entire lifecycle in one growing season.
Seeds from last year lie dormant in the soil, waiting for the right conditions. Seeds remain viable for 3+ years.
Your Move: This is your window to apply pre-emergent before germination.
When soil temperature reaches 55°F for several consecutive days, seeds begin to germinate. Germination continues through early summer.
Your Move: Pre-emergent must be down BEFORE this happens. Once germinated, it's too late for prevention.
Young crabgrass grows aggressively, spreading horizontally and producing tillers. A single plant can cover 1-3 square feet.
Your Move: Post-emergent herbicides work best at this stage (1-4 tillers).
Mature plants produce distinctive finger-like seed heads. A single plant can produce 150,000 seeds.
Your Move: Post-emergent still works but requires higher rates and multiple applications. Prevent seeds from spreading.
Crabgrass dies with the first hard frost, leaving behind bare spots and thousands of seeds for next year.
Your Move: Overseed bare spots to prevent next year's crabgrass from filling them.
Prevention Strategy: Pre-Emergent Herbicides
Pre-emergent herbicides are the cornerstone of crabgrass control. They create a chemical barrier in the top layer of soil that kills germinating seeds before they emerge. Applied correctly, pre-emergents prevent 95%+ of crabgrass.
When to Apply Pre-Emergent
Timing is everything. Apply too early and the product degrades before crabgrass germinates. Too late and crabgrass is already growing.
Method 1: Soil Temperature (Most Accurate)
Apply when soil temperature at 2-4 inch depth reaches 55°F for 3-5 consecutive days. Use a soil thermometer or check your local extension service's GDD (Growing Degree Day) tracker.
Method 2: Forsythia Rule (Easy Reference)
Apply when forsythia bushes are blooming with bright yellow flowers. This natural indicator coincides with the 55°F soil temperature threshold in most regions.
Method 3: Regional Calendar (Approximate)
See the Regional Timing Calendar below for approximate dates by location.
Application Tips
Calculate Your Lawn Size
Measure your lawn area accurately. Most products are applied at 2-4 lbs per 1,000 sq ft. Under-applying reduces effectiveness; over-applying wastes money.
Calibrate Your Spreader
Set your spreader according to the product label. Do a test run on your driveway to verify the rate. Different spreaders require different settings.
Apply in Two Passes
For even coverage, apply half the product walking north-south, then the other half walking east-west. This prevents stripes and gaps.
Water In Within 48 Hours
Most pre-emergents need 0.5 inches of water to activate and move into the soil. Rain works, or run your sprinklers. Without watering, the product sits on the surface and degrades.
Don't Disturb the Barrier
Avoid core aeration, dethatching, or heavy raking after applying pre-emergent. These break the chemical barrier and let crabgrass through.
Consider a Split Application
In areas with long summers, apply half the rate in early spring and half 8-10 weeks later. This extends protection through summer's extended germination window.
Pre-Emergent Herbicide Comparison
All of these active ingredients effectively prevent crabgrass when applied at the right time. Your choice depends on how long you need control and whether you plan to seed.
| Active Ingredient | Brand Names | Control Duration | Can Seed After? | Best For |
|---|---|---|---|---|
| Prodiamine | Barricade, Crabgrass Barrier | 6-9 months | Wait 4-6 months | Longest control, professional choice |
| Dithiopyr | Dimension | 4-5 months | Wait 3-4 months | Also kills very young crabgrass (post-emergent activity) |
| Pendimethalin | Scotts Halts, Pendulum | 3-4 months | Wait 3-4 months | Widely available at retail, proven performer |
| Mesotrione | Tenacity | 4-6 weeks per app | Safe with seeding | Only option when overseeding in spring |
Product Selection Tips
- For maximum protection: Prodiamine (Barricade) at the high rate provides the longest residual control—ideal for hot climates with extended crabgrass season.
- If you're a week late: Dithiopyr (Dimension) has early post-emergent activity and can kill crabgrass in the "white root" stage just after germination.
- For spring seeding: Mesotrione (Tenacity) is the only pre-emergent safe to use when establishing new grass from seed. Note: requires more frequent reapplication.
- On a budget: Pendimethalin products (Scotts Halts) are effective and widely available at big box stores.
Post-Emergent Treatment: Killing Active Crabgrass
If crabgrass is already growing, pre-emergent won't help—you need post-emergent herbicides. Timing and technique matter for best results.
Treatment Success by Growth Stage
1-4 Tillers (Best)
Young crabgrass with just a few leaf blades. Most herbicides work quickly with a single application.
Success Rate: 90-95%
5-10 Tillers (Moderate)
Established but not yet flowering. May require a second application 10-14 days later.
Success Rate: 75-85%
Mature with Seed Heads (Difficult)
Large plants with visible seed heads. Requires higher rates and multiple applications. Consider removal and overseeding instead.
Success Rate: 50-70%
Post-Emergent Application Tips
Post-Emergent Herbicide Comparison
These products kill crabgrass that's already growing. Always check the label for your grass type—some herbicides damage certain lawn grasses.
| Active Ingredient | Brand Names | Safe On | NOT Safe On | Notes |
|---|---|---|---|---|
| Quinclorac | Drive XLR8, Quincept | Most lawns: Bermuda, Zoysia, Fescue, Bluegrass, Ryegrass | St. Augustine, Bahiagrass, Centipede, Floratam | Most versatile option. Also controls some broadleaf weeds. |
| Fenoxaprop | Acclaim Extra | Kentucky Bluegrass, Perennial Ryegrass, Fine Fescue | Tall Fescue, Bermuda, St. Augustine, Zoysia | Very effective but grass-type restrictions are strict. |
| Mesotrione | Tenacity | Most cool-season grasses | Bermuda, Zoysia, St. Augustine, Centipede | Turns crabgrass white before killing. Also works as pre-emergent. |
| MSMA | (Restricted) | Bermuda, Zoysia | Cool-season grasses, St. Augustine | Very effective but banned in some states. Check local regulations. |
Cultural Controls: Beat Crabgrass Without Chemicals
A healthy, dense lawn is your best long-term defense. These practices make your lawn naturally resistant to crabgrass invasion.
Mow High
This is the #1 cultural control. Mow at the upper end of your grass type's recommended height:
- Cool-season grasses: 3-4 inches
- Bermuda: 1-2 inches
- Zoysia: 1.5-2.5 inches
- St. Augustine: 3-4 inches
Taller grass shades the soil, blocking the light crabgrass seeds need to germinate.
Water Deeply, Infrequently
Deep watering (1 inch per week) encourages deep grass roots. Shallow, frequent watering favors crabgrass with its shallow root system.
Water early morning so grass blades dry during the day.
Fertilize Correctly
A properly fed lawn grows thick and crowds out weeds. Follow your grass type's fertilization schedule—but don't over-fertilize, which can actually encourage some weeds.
Overseed Thin Areas
Bare or thin spots are invitations for crabgrass. Fill them in with grass seed in fall (or spring with Tenacity). Dense turf leaves no room for weeds.
Aerate Compacted Soil
Compacted soil stresses grass but doesn't bother crabgrass. Core aerate in fall to improve grass health. Don't aerate after applying pre-emergent.
Maintain Sharp Mower Blades
Dull blades tear grass, creating brown tips that weaken the lawn. Sharpen blades every 20-25 hours of mowing.
Regional Pre-Emergent Timing Calendar
These are approximate windows based on historical soil temperature data. Always verify with actual soil temperature for best results.
| Region | First Application | Second Application (Optional) | Natural Indicator |
|---|---|---|---|
| Deep South (FL, Gulf Coast) | Mid-February to Early March | Late April to May | Azaleas blooming |
| Southeast (GA, SC, NC) | Early to Mid-March | Mid-May | Forsythia starting to bloom |
| Transition Zone (TN, VA, MD, KY) | Mid-March to Early April | Late May to Early June | Forsythia in full bloom |
| Midwest (OH, IN, IL, MO) | Late March to Mid-April | Early June | Forsythia blooming |
| Northeast (NY, PA, NJ, New England) | Mid-April to Early May | Mid-June | Forsythia/lilac blooming |
| Upper Midwest (MN, WI, MI) | Late April to Mid-May | Late June | Lilacs blooming |
| Southwest (TX, AZ, NM) | Early February to March | May (if needed) | Soil temperature monitoring recommended |
| Pacific Northwest (WA, OR) | Late March to April | Not usually needed | Cherry trees blooming |
Grass-Type Specific Advice
Your grass type affects which products you can use and how aggressively you can treat crabgrass.
Cool-Season Grasses
Kentucky Bluegrass, Tall Fescue, Fine Fescue, Perennial Ryegrass
Pre-emergent: All major pre-emergents work well. Prodiamine or pendimethalin are safe choices.
Post-emergent: Quinclorac is generally safe. Fenoxaprop works on bluegrass/ryegrass but damages tall fescue. Tenacity works but may cause temporary whitening.
Special notes: Fall overseeding? Apply pre-emergent in spring only, or use Tenacity which allows seeding.
Bermuda Grass
Common Bermuda, Hybrid Bermuda varieties
Pre-emergent: All work well. Prodiamine is the professional standard. Can apply at full rates.
Post-emergent: Quinclorac and MSMA (where legal) are effective. Bermuda recovers quickly from treatments.
Special notes: Bermuda's aggressive growth helps crowd out crabgrass. Focus on density through proper fertilization.
Zoysia Grass
Zoysia japonica, Zoysia matrella varieties
Pre-emergent: All major pre-emergents are safe. Split applications work well for extended dormancy periods.
Post-emergent: Quinclorac is safe. MSMA (where legal) works. Avoid fenoxaprop.
Special notes: Zoysia's dense growth naturally resists crabgrass once established. Patience during establishment years.
St. Augustine Grass
Floratam, Palmetto, Raleigh, Seville
Pre-emergent: Pendimethalin and prodiamine are safe. Apply at lower rates if concerned.
Post-emergent: Very limited options. Quinclorac CANNOT be used. Fenoxaprop CANNOT be used. Hand-pulling or targeted treatment with sethoxydim may work.
Special notes: Prevention is critical since post-emergent options are limited. Maintain thick turf as primary defense.
Centipede Grass
Eremochloa ophiuroides
Pre-emergent: Use pendimethalin or prodiamine at label rates. Centipede is sensitive—don't over-apply.
Post-emergent: Limited options similar to St. Augustine. Quinclorac can damage centipede. Sethoxydim is safer.
Special notes: Centipede is slow-growing, so damage takes longer to recover. Focus heavily on prevention.
Cost Analysis: DIY vs. Professional
Here's what to expect to spend on crabgrass control for a typical 5,000 sq ft lawn.
DIY Approach
- Pre-emergent (granular) $15-30
- Post-emergent (if needed) $10-25
- Spreader (one-time) $25-50
- Your time 1-2 hours
Professional Service
- Pre-emergent application $50-100
- Second application $50-100
- Post-emergent (if needed) $50-75
- Your time 0 hours
Common Mistakes to Avoid
Applying Too Late
Pre-emergent must be down BEFORE soil hits 55°F. By the time you see crabgrass, it's too late for prevention. Set a calendar reminder for early spring.
Skipping the Second App
In warmer climates, a single application may not last through extended germination. A split application 8-10 weeks later provides season-long protection.
Not Watering In
Pre-emergent sitting on the surface does nothing. It needs 0.5 inches of water within 48 hours to move into the soil where seeds germinate.
Aerating After Pre-Emergent
Core aeration punches holes through the chemical barrier, creating pathways for crabgrass. Aerate in fall, not spring after pre-emergent application.
Mowing Too Low
Short grass = hot soil = crabgrass heaven. Raise your mowing height to 3-4 inches (for most grasses) to shade out weed seeds.
Ignoring Thin Spots
Bare areas get colonized first. Overseed in fall to thicken your lawn. A dense lawn is your best natural defense.
Wrong Post-Emergent for Grass Type
Using quinclorac on St. Augustine or fenoxaprop on tall fescue will damage your lawn. Always check the label for your specific grass type.
Giving Up After One Year
Crabgrass seeds last 3+ years in soil. You need consistent pre-emergent applications for 2-3 years to exhaust the seed bank. Stick with it!
Frequently Asked Questions
When should I apply pre-emergent for crabgrass?
Apply pre-emergent when soil temperatures reach 55°F for 3-5 consecutive days, typically when forsythia bushes bloom. In the South, this is February-March; in the North, April-May. A second application 8-10 weeks later provides extended protection.
Can I kill crabgrass that's already growing?
Yes, post-emergent herbicides containing quinclorac (Drive XLR8) or fenoxaprop (Acclaim Extra) effectively kill emerged crabgrass. Treatment works best when crabgrass has 1-4 tillers (leaf blades). Mature crabgrass with seed heads is harder to kill and may require multiple applications.
Why does crabgrass keep coming back every year?
Crabgrass is an annual weed that dies each winter but produces thousands of seeds per plant. These seeds survive in soil for 3+ years. If you miss the pre-emergent window, those seeds germinate when soil warms. Consistent pre-emergent applications for 2-3 years depletes the seed bank.
Will pre-emergent prevent me from seeding my lawn?
Yes, most pre-emergents prevent all seed germination, including grass seed. Wait 8-16 weeks after application before seeding (check product label). Alternatively, use Tenacity (mesotrione) which prevents crabgrass while allowing new grass seed to establish.
What's the best pre-emergent herbicide for crabgrass?
Prodiamine (Barricade) offers the longest control (6-9 months) and is the professional's choice. Dithiopyr (Dimension) is excellent and can kill very young crabgrass. Pendimethalin (Scotts Halts) is widely available at retail. All work well when applied at the right time.
Does mowing height affect crabgrass?
Mowing high (3-4 inches for most grasses) is one of the best cultural controls. Taller grass shades the soil, preventing crabgrass seeds from getting the light they need to germinate. Low-mowed lawns have significantly more crabgrass problems.
Is crabgrass bad for my lawn?
Crabgrass aggressively competes with desirable grass for water, nutrients, and sunlight. It spreads rapidly via tillers and can crowd out your lawn. When it dies in fall, it leaves bare patches that can erode or be invaded by other weeds over winter.