How Do I Kill Crabgrass and Other Unwanted Grass?

July 9, 2026 / Ria Carrington / Weed Elimination

You saw that first patch of crabgrass and your heart sank a little. I get it. But you can fix this.

We will cover identifying your exact weed, using pre-emergents to stop new weeds, choosing the right post-emergent herbicides for killing existing problems, how to manually remove invaders, and the simple steps to keep them from coming back.

I’ve pulled plenty of it from my own lawn, learning what works with help from my mower, Max, and a stubborn patch I call Patch.

Table of Contents

At a Glance: Key Takeaways

Before we get into the weeds, here are the main things to remember. I keep these basics in mind every spring when I fire up Max for the first cut.

You must identify your problem grass correctly before you do anything else; the wrong treatment wastes time and money.
Stopping weed seeds from ever sprouting with a pre-emergent is far easier than killing established, spreading plants.
A thick, healthy lawn is your most powerful, long-term defense, as it leaves no room for invaders to take root.
The fight happens on two fronts: stop new seeds (pre-emergent control) and kill what’s already growing (post-emergent control).

Spotting the Enemy: What to Look For

You can’t win a fight if you don’t know who you’re fighting. Crabgrass and other unwanted grasses have tells. Get down on one knee and take a close look.

Crabgrass looks out of place. It’s usually a lighter, yellower green than your lawn grass. Feel a blade. It’s coarser, almost like a thin piece of plastic. Its growth habit is the real giveaway: it grows low and sprawls outward from a central point, like a green starfish flattening itself on your soil. It doesn’t grow in neat, upright clumps.

Other common invaders include nimblewill, which has thin, wiry stems and a blue-green hue, and coarse tall fescue clumps that feel bumpy underfoot. In cool-season lawns, Bermuda grass is a fierce invader with fine blades that form a dense, creeping mat.

Here’s a simple trick I use in Patch’s corner, the tug test. Grab a handful of the suspect grass and give a firm, steady pull. Most weed grasses with runners or rhizomes (underground stems) will resist and not come up cleanly. Your good grass usually pulls up more easily, roots and all.

Why Correct Identification is Your First Battle

Choosing a weed killer is not one-size-fits-all. Some products only work on certain grass types. Using the wrong one might kill your good grass while leaving the weed untouched. I’ve seen it happen. To avoid this, take a moment to identify your lawn’s grass type and the common weeds you’re fighting. That quick step—identifying lawn weeds and grass types—can steer you toward the right product.

Sometimes, the “weed” is just a desirable grass growing where you don’t want it, like Bermuda grass creeping into a fescue lawn. This changes your strategy completely, as you need a selective herbicide that targets one type of grass without harming the other. Knowing your enemy is the first, non-negotiable step to getting your lawn back. To tailor your approach, start with lawn weed identification and treatment so you know which product and timing will work. A quick guide to identifying common lawn weeds helps you plan an effective, targeted treatment.

Why Your Lawn is Vulnerable

Close-up of dense green lawn grass blades, illustrating how bare spots and thin turf can allow crabgrass to invade.

Crabgrass and other unwelcome grasses don’t just show up. They move into neighborhoods where your good grass is struggling. Think of your lawn like a team. If your star players are weak, the benchwarmers take the field. Here are the main reasons your lawn gets invaded, and the simple fixes to give your turf the home-field advantage.

Thin Turf: Bare dirt is an open invitation. Grass seed, whether from your neighbor’s lawn or a weed, needs soil contact to grow. A thin lawn lets light and space reach the soil.
The fix is straightforward: overseed in the fall to fill in those gaps with the grass you actually want.
Compacted Soil: This is a big one. When soil is packed down, water and air can’t reach grass roots. Your lawn grass suffocates, but tough weeds like crabgrass punch right through. Try the screwdriver test. If you can’t push a standard screwdriver easily into the ground, it’s compacted.
Core aeration once a year solves this, letting your lawn breathe and drink deeply.
Low Mowing Height: Cutting your grass too short is like giving it a buzz cut. It stresses the plant, exposes soil to sun, and encourages low-growing weeds. I learned this the hard way with Max, my mower. I dropped the deck too low one spring and paid for it all summer.
Mow high. For most grasses, keep the blade at 3 inches or higher to shade the soil and build stronger roots.
Overwatering: Frequent, shallow watering trains your grass to have shallow roots. It also creates a perfect, damp nursery for weed seeds. My drip system, Sunny, taught me that deep, infrequent soakings are the way to go.
Water deeply once or twice a week, encouraging roots to grow down where it’s cooler and more resilient.
Improper Fertilization: Underfeeding starves your grass. Overfeeding, especially with quick-release nitrogen, can burn it and create a surge of growth that weakens it. Both scenarios open the door for weeds.
Feed your lawn based on a soil test. It’s the only way to know exactly what it needs.

The Two-Pronged Attack: Prevention and Removal

Fighting unwanted grass is a two-part battle. You need to stop the next generation from sprouting while you deal with the weeds that are already partying on your property. Tackle both, and you’ll win the war.

How Do I Stop It From Coming Back?

This is all about pre-emergent herbicides. These products don’t kill existing plants. Instead, they form a thin barrier in the top layer of soil that stops seeds from developing roots after they germinate. It’s like putting a security system on your lawn’s soil.

The golden rule for timing is to apply when soil temperatures consistently hit 50-55°F for several days in a row. A good backyard sign is when the buds on your maple trees start to swell. If you apply too late, after seeds have sprouted, it won’t work.

For an organic route, corn gluten meal is a popular option. It provides a little nitrogen and can inhibit some seed growth. Its performance is weaker and less consistent than synthetic options, but it’s a safe choice for gardens with pets and kids playing.

Never forget, the best pre-emergent you have is a thick, healthy lawn. Proper mowing, watering, and feeding create a living mat that blocks light and out-competes weeds naturally. All my work with Patch, that shady corner, proved that building health is the long-term solution.

When to Apply Pre-Emergent for Your Grass Type

Cool-Season Lawns (Kentucky Bluegrass, Fescue, Rye): Target early spring. That soil temp window of 50-55°F is your cue. In many areas, this is when forsythia bushes start to bloom.
Warm-Season Lawns (Bermuda, Zoysia, St. Augustine): Apply in late spring, as soil temperatures are warming toward 70°F. This is often when azaleas are in full bloom.

You can also use a split application. Put down half the recommended rate in early spring, and the other half about 8 weeks later. This extends the protective barrier further into the growing season.

How Do I Kill Crabgrass and Unwanted Grass Already in My Lawn?

For plants that have already broken through, you shift to removal. You have two main tools: your hands and post-emergent herbicides.

For a small patch of crabgrass, hand-pulling works if you do it right. Don’t just yank the leaves. Get your fingers down to the base, feel for the central crown, and pull it all out. A weeding tool like a fishtail or stand-up weeder makes this easier on your back.

When you’re facing a large invasion, a selective post-emergent herbicide is your best bet. These chemicals are designed to kill specific types of plants (like crabgrass) without harming your lawn grass. Look for ingredients like quinclorac, which is excellent for crabgrass.

This directly answers a common question: does Roundup for lawns kill crabgrass? You must read the label carefully. Standard Roundup is non-selective; it will kill every plant it touches, including your grass. However, there are “Roundup for Lawns” products that are selective and will target weeds while being safe for listed grass types. Always, always check the label.

Killing invasive Bermuda grass in a cool-season lawn is a special challenge. It’s a persistent, spreading grass. You’ll likely need multiple applications of a selective herbicide over two or three growing seasons to truly suppress it. It’s a marathon, not a sprint. Shaded lawns add another layer of complexity, since light and moisture patterns affect weed growth. For those sites, shaded-lawn weed-control strategies can change the approach and timing of treatments.

The Step-by-Step Removal Process

Identify the weed. Know if it’s crabgrass, dallisgrass, or something else. A quick photo search can help.
Choose a product labeled for that weed AND safe for your type of lawn grass. This is the most critical step. Applying the wrong herbicide can damage your entire lawn.
Apply on a calm, clear day. No rain in the forecast for 24 hours and wind under 5-10 mph to prevent drift.
Wait. Most herbicides take 7-14 days to show full effect. The weeds will turn white or brown as they die.
Reseed bare spots in the fall. Once the weed is gone, you’ll have an empty patch. Fall is the best time to fill it in with new, good grass seed to prevent the cycle from repeating.

Keep pets off the treated area until the spray has completely dried. Once dry, the product has bonded to the plant leaves, making it much safer for your furry friends to return.

Common Mistakes When Fighting Crabgrass (And How to Avoid Them)

Wide view of a well-kept suburban front lawn with a brick house, a long green lawn, and a driveway on the left.

I’ve made most of these errors myself. Fighting crabgrass can feel like a game of whack-a-mole if you’re not playing by the right rules. Let’s fix that.

Mowing Too Short. A scalped lawn is a stressed lawn. It opens the soil to sunlight, which is an invitation for crabgrass seeds to sprout. Keep your mower deck high and mow often, removing only the top third of the grass blade each time. This shades the soil and helps your good grass outcompete the invaders.
Using the Wrong Herbicide. Spraying a general “weed killer” on mature crabgrass often just singes the leaves. The plant laughs and grows back. You need a herbicide specifically labeled for crabgrass or grassy weeds, often containing quinclorac. It gets down into the roots for a complete kill.
Applying Pre-Emergent Too Late. Timing is everything. If you put down your preventative barrier after the seeds have already woken up and sprouted, you’ve wasted your time and money. Apply pre-emergent when soil temperatures consistently hit 50-55°F, which is often when forsythia bushes start to bloom.
Ignoring Soil Health. Crabgrass thrives in thin, compacted soil where your lawn grass struggles. Fighting weeds starts from the ground up with annual core aeration and proper fertilization. Healthy soil grows thick grass that leaves no room for weeds.
Expecting One Application to Solve Everything. This is a marathon, not a sprint. A single treatment might clean things up for a season, but seeds live in your soil for years. Crabgrass control is a yearly cycle of prevention in spring and spot treatment in summer. Consistency is your greatest weapon.

My shady corner, “Patch,” taught me this last lesson the hard way. I kept nuking the same crabgrass every July, frustrated it kept returning. I finally realized I was only treating the symptom, not the cause. The soil was compacted and the grass was thin. One season of aeration, overseeding, and a timely spring pre-emergent changed everything. Now “Patch” is just a nickname, not a reality.

Choosing Your Tools: Herbicide Types Explained

Walking into the garden center can be overwhelming. All these bottles and bags make big promises. Let’s break down what you’re actually looking at so you can choose with confidence.

Pre-Emergent vs. Post-Emergent

This is the most important difference. Think of pre-emergent as locking your door to prevent a break-in. Think of post-emergent as calling the police after someone is already inside.

Pre-emergent herbicides create a barrier in the top layer of soil that stops weed seeds from sprouting. They do nothing to weeds you can already see.
Post-emergent herbicides are applied to the leaves of active, growing weeds to kill them. They do nothing to prevent new weeds from coming later.

Selective vs. Non-Selective

This tells you what the product will kill.

Selective herbicides target specific plant types, like grassy weeds or broadleaf weeds, while leaving your lawn grass unharmed. Most crabgrass killers are selective for grasses.
Non-selective herbicides, like glyphosate, will kill almost any plant they touch. Use these only for spot treatment in gravel or on driveway cracks, never across your lawn.

Liquid Concentrate vs. Granular Products

This is about the form it comes in and how you apply it.

Liquid Concentrate	Granular Product
You mix it with water in a sprayer.	Comes ready to spread with a broadcast or drop spreader.
Pros: Very precise application, excellent for spot-treating patches, often more cost-effective for large areas.	Pros: Much easier for most homeowners, no mixing required, less risk of drift on windy days.
Cons: Requires a sprayer, needs careful calibration, can drift onto garden plants if you’re not careful.	Cons: Less precise, must be watered in immediately to activate, often more expensive per application.

For a few crabgrass patches, a ready-to-spray bottle of selective post-emergent herbicide is the simplest fix. For a full-lawn pre-emergent application in early spring, a granular product combined with fertilizer is often the easiest path for most homeowners. These approaches are among the best lawn pest weed control solutions for keeping your lawn healthy and weed-free.

A Note on Pet and Pollinator Safety

This isn’t just a feel-good tip. It’s a core part of responsible lawn care. I share my yard with dogs and bees, and I bet you do too.

Always read the entire product label, not just the front, and follow the re-entry time instructions to the letter. This tells you how long to keep pets and people off the grass after an application. If you use granules, water them in as directed. This activates the product and helps it settle into the soil, away from paws.

Apply any product in the late evening when bees and other pollinators have returned to their hives and are less active. Early morning is the next best time.

The safest strategy of all is to nurture a thick, healthy lawn that naturally resists invasion, reducing your need for any chemicals. Every step that makes your grass stronger—proper mowing, feeding, and watering—is a step toward a safer yard for everyone who uses it.

Greedy Grass FAQs: Your Crabgrass Questions, Answered

A person using a hose-end sprayer to apply lawn treatment on a green lawn, viewed from above

Can I apply pre-emergent and post-emergent herbicide at the same time?

Don’t do it. Apply your pre-emergent in early spring to stop seeds, then use a post-emergent in summer only on the patches that sneak through. Mixing strategies just wastes product and effort.

Should I pull out the dead, brown crabgrass after a herbicide treatment?

Nope, leave it be. The dead plant will break down and add organic matter. Your real job is to overseed that area in the fall so your good, greedy grass fills the space first.

Does hand-pulling crabgrass work, or does it just spread more seeds?

It works only if you get the entire root system out. If you just snap off the top, it grows back angrier. For a few plants, get a weeding tool and be thorough.

How soon can I plant new grass seed after using a crabgrass killer?

Patience is key. Most herbicides require a waiting period, often 3-4 weeks, before seeding. Always check your product label first, but fall is the absolute best time to overseed for success.

Will crabgrass just die on its own when it gets cold?

Yes, it’s an annual that dies with frost, but don’t celebrate yet. Before it dies, a single plant can drop thousands of seeds for next year. That’s why a spring pre-emergent is non-negotiable.

Your Path to a Cleaner Lawn

Close-up of yellow dandelions among dark green lawn blades.

The biggest win comes from stopping these grasses before they start. A well-timed pre-emergent in spring and a thick, healthy lawn from proper mowing and feeding are your best defenses.

Always choose pet-safe and pollinator-friendly products when you need to treat a problem. Your lawn is a living part of your home’s ecosystem, and learning its rhythms each season is the most rewarding part of the job.

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Written by Ria Carrington. Ria is an avid lawn care enthusiast and advisor. No lawn is unsalvagable when Ria is at work. She has helped countless homeowners breath new life into their dying lawns. She has a B.Sc in Agriculture and brings practical advice combined with knowledge of plant science and her decade worth of hands on experience.