What Fertilizer Kills Crabgrass

The best fertilizer to kill crabgrass is a pre-emergent crabgrass preventer fertilizer, not a standard feeding formula.
 
These combination products, often called weed and feed fertilizers, contain a pre-emergent herbicide that stops crabgrass seeds from sprouting.
 
If you’re searching for what fertilizer kills crabgrass, the answer lies in timing and the active ingredient, not just the fertilizer itself.
 
In this post, we’ll break down how these crabgrass-killing fertilizers work, when to apply them, and what to look for in a product.
 
Let’s dig into the details so your lawn stays thick and crabgrass-free.
 

What Fertilizer Kills Crabgrass Before It Starts

The fertilizer that kills crabgrass works by creating a barrier in the top layer of soil.
 
This barrier is a pre-emergent herbicide, and it’s the active ingredient that makes the fertilizer effective against crabgrass.
 
When you apply a crabgrass preventer fertilizer, you’re not killing existing weeds; you’re stopping new seeds from germinating.
 
That’s the key difference between a standard fertilizer and one designed to kill crabgrass.
 
A regular fertilizer just feeds the grass, but a weed and feed fertilizer combines nutrients with a herbicide to target crabgrass specifically.
 

1. Pre-Emergent Herbicides Are the Active Killers

The actual “killer” in a crabgrass-killing fertilizer is a pre-emergent herbicide like dithiopyr, pendimethalin, or prodiamine.
 
These ingredients work by inhibiting root development in young crabgrass seedlings.
 
When crabgrass seeds germinate, they absorb the herbicide from the soil, and their roots fail to develop properly.
 
Without strong roots, the young crabgrass plants die quickly, often before they even break the surface.
 
So, what fertilizer kills crabgrass? Any product with these active ingredients, combined with a nitrogen-rich fertilizer base, does the job.
 

2. The Fertilizer Part Feeds Your Lawn

While the herbicide kills crabgrass, the fertilizer part feeds your desirable grass.
 
A thicker, healthier lawn is your best defense against crabgrass because it leaves little room for weeds to establish.
 
A crabgrass preventer fertilizer often contains nitrogen, phosphorus, and potassium to promote vigorous turf growth.
 
This dual action is why many homeowners prefer a weed and feed product over separate treatments.
 
You get the crabgrass-killing power and the lawn-feeding benefits in one application.
 

3. Timing Matters for the Best Kill

The fertilizer that kills crabgrass only works if you apply it before the seeds germinate.
 
Timing is everything, and you need to get this product down in early spring.
 
A good rule of thumb is to apply when soil temperatures reach about 55°F for several consecutive days.
 
You can check soil temperature with a simple probe or look for a local extension service update.
 
If you apply too late, the crabgrass will already be growing, and a pre-emergent won’t kill it.
 
In that case, you’d need a post-emergent herbicide instead of a fertilizer.
 

The Best Fertilizer to Kill Actively Growing Crabgrass

If you missed the early spring window, standard pre-emergent fertilizers won’t help.
 
For actively growing crabgrass, you need a different type of product.
 
What fertilizer kills crabgrass that’s already visible? The answer is a post-emergent herbicide, but you can find combination products.
 
These products often combine a post-emergent herbicide with a light feeding formula.
 
However, many lawn care experts recommend applying a straight post-emergent herbicide first.
 
Then, you can follow up with a regular fertilizer once the crabgrass is dead.
 

1. Look for Quinclorac or Fenoxaprop

When you need to kill existing crabgrass, look for active ingredients like quinclorac or fenoxaprop-p-ethyl.
 
These are post-emergent herbicides that target crabgrass after it has sprouted.
 
Some products combine these with a small amount of fertilizer, but the herbicide is doing the killing work.
 
You’ll spray these directly on the crabgrass, and it will die within a couple of weeks.
 
This is not a fertilizer that kills crabgrass in the traditional sense, but it does get the job done.
 

2. Why Post-Emergent Products Aren’t “Feed” Products

A true weed and feed fertilizer is designed for prevention, not control of existing weeds.
 
If you apply a pre-emergent crabgrass fertilizer to mature crabgrass, you’ll just be feeding your weeds.
 
That’s why it’s crucial to identify the growth stage of your crabgrass first.
 
For young crabgrass with less than five tillers, some pre-emergents like dithiopyr can offer early post-emergent control.
 
But for larger plants, you’ll need a dedicated post-emergent herbicide, not a fertilizer.
 

How to Apply a Crabgrass Killer Fertilizer Correctly

Applying the right fertilizer only works if you do it correctly.
 
You want even coverage so the herbicide barrier doesn’t have gaps.
 
Use a broadcast spreader for granular crabgrass preventer fertilizers.
 
Walk in a steady, overlapping pattern to ensure every square foot gets covered.
 
After applying, water the lawn lightly to activate the herbicide.
 
This helps the active ingredient wash into the soil where crabgrass seeds are waiting.
 

1. Avoid Splitting Applications for Heavy Lawns

On heavy clay soils, one application might not be enough.
 
You can split the application into two rounds, with the first in early spring and the second about six to eight weeks later.
 
This extends the herbicide barrier and gives you longer-lasting protection.
 
But be careful not to over-apply, as too much herbicide can harm your lawn’s roots.
 
Follow the label instructions for your specific crabgrass-killing fertilizer.
 

2. Don’t Mow Right After Applying

Wait at least two days after applying a granular fertilizer before you mow.
 
Mowing too soon can pick up the granules and redistribute them unevenly.
 
Also, hold off on watering for 24 hours if you’re using a liquid post-emergent product.
 
This gives the herbicide time to stick to the crabgrass leaves and be absorbed.
 
Residual fertilizer granules need water to activate, but liquid sprays need time to dry.
 

So, What Fertilizer Kills Crabgrass Best?

The best fertilizer to kill crabgrass is a pre-emergent weed and feed product applied in early spring.
 
Fertilizers with dithiopyr, prodiamine, or pendimethalin effectively kill crabgrass seeds before they sprout.
 
For already established crabgrass, you’ll need a post-emergent herbicide, not a typical fertilizer.
 
So, to directly answer what fertilizer kills crabgrass: it’s the one with a pre-emergent herbicide combined with lawn food.
 
Use it at the right time, follow the application steps, and you’ll prevent crabgrass all season long.
 
Hope this clears up how to choose the right crabgrass-killing fertilizer for your lawn.