When to Apply a Pre-Emergent Crabgrass Preventer [ Before or After Rain & Wet Grass?]

When trying to get rid of crabgrass, it’s important to know when to apply a pre-emergent crabgrass preventer, before or after rain and on wet grass.

I apply a crabgrass pre-emergent right before it’s forecasted to rain, if possible. The rain will wash the treatment off the grass blades and water the preventer into the soil. If it doesn’t rain, water the chemical into the soil.

The following guide will help you get the treatment spot on.

Snapshot Granular
Syngenta Tenacity Turf Herbicide
Barricade 65 WDG Pre-Emergent Herbicide
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Syngenta Tenacity Herbicide - Pre-Emergent and Post-Emergent Weed...
Quali-Pro Prodiamine, Pre-Emergent Herbicide, 5 lbs, Yellow...
Snapshot Granular
DOW Snapshot 2.5 TG Granular Pre-emergent Herbicide
Syngenta Tenacity Turf Herbicide
Syngenta Tenacity Herbicide - Pre-Emergent and Post-Emergent Weed...
Barricade 65 WDG Pre-Emergent Herbicide
Quali-Pro Prodiamine, Pre-Emergent Herbicide, 5 lbs, Yellow...

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When to apply crabgrass preventer

Three things will help you know it is the right time to apply a crabgrass preemergent herbicide:

  • Season – early spring
  • Soil temperature rising to about 55 °F
  • When the weather forecast shows it’s about to rain.

Here’s a quick infographic with the guide. I’ve explained in detail below the graphic.

When to apply crabgrass preemergent - before or after rain and when grass is wet

Crabgrass is an annual weed. As such, it spreads by seed and not through rhizomes. You want to control crabgrass by preventing its germination with a pre-emergent, otherwise, killing full-grown weeds can be very difficult.

Timing Tips to Put Down Crabgrass Pre-emergent

There are various methods you can use to know the right time to put down pre-emergent in your lawn. While most people choose to use a weather map, the method can be erratic because the forecast is usually for the larger region and not your specific area.

The timing should, therefore, be on point, but how do you know when to apply crabgrass preventer? Here are a few pointers to help you with the timing:

Early Spring Season

Crabgrass germinates from seeds that drop in summer or fall. These seeds stay in the soil through winter and start germinating when the weather starts to get warm – usually during spring.

To prevent crabgrass from germinating in your lawn, apply a pre-emergent early spring because this is the time when the weed will start to sprout in your lawn. The University of Arizona says to apply pre-emergents when the temperature is high enough for the seed to take water but before any germination.

Any time between late March and early April is the perfect time to put down a preemergent herbicide such as Snapshot to give you protection all season long.

DOW Snapshot 2.5 TG Granular Pre-emergent Herbicide
  • Snapshot 2.5 boasts more control than any other pre-emergent herbicide on the market
  • Up to 6-8 months of control for 111 broadleaf and grassy weeds
  • Application rate: 2.3 to 4.6 lb per 1000 square feet

Affiliate links and images pulled from the Amazon Product Advertising API on: 2024-06-11

If you’re late, you can still do this in early May.

Apply in early spring to prevent the germination of crabgrass, chickweed, poa annua, and other common lawn weeds before they start to spread. Apply before the 3rd or 4th mowing to protect all season long. Scott’s Turf Builder Halts Crabgrass (label).” – Scotts

Warm Soil Temperature

Spring is when the sun starts to come out. This is when a lot of plants germinate because the heat from the sun warms up the soil, activating enzymes that stimulate seed germination.

Crabgrass seeds start to germinate when the soil temperature reaches about 55 °F to 60 °F, usually from late spring through to mid-summer.

Soil temperature may sometimes be affected by other factors such as wind, shade in your lawn, and the general climate of where you live. So be sure to take soil temperatures daily as soon as March starts.

The best time to put down your pre-emergent is when the soil temperature is around 55°F to inhibit the root development of the germinating crabgrass seeds. This will go a long way in helping you control this tenacious grass weed for the whole season ahead.

Before or After Rain?

The best time to apply crabgrass preventer is before the rain. After it rains, the preventer will have been washed into the soil and crabgrass seeds to stop them from developing roots and germinating. If you apply after rain, water your lawn immediately after to wash the pre-emergent into the soil.

When the rain comes, it will wash the herbicide into the soil and the crabgrass seed killing it before germination.

You should be careful not to apply crabgrass preemergent herbicide too early because it will break down and become less effective.

The best crabgrass pre-emergent products indicate that it is a good practice to water the lawn a few days after application to wash off the concentrate into the soil. The herbicide provides important information about the herbicide so it’s important to read it before application.

Pro tip: Follow your local weather forecast closely. As soon as the forecast shows it will rain in a few hours, start putting down a crabgrass preventer on your lawn. In case it does not rain 2 to 3 days after application, ensure that you apply water on the herbicide as per the instructions on the product’s label.

When to apply crabgrass preventer

Read Herbicide Labels

The best way to determine a good time to put down a pre-emergent herbicide for preventing weeds such as crabgrass, foxtail, and goosegrass is to read the label of your preferred herbicide.

Each manufacturer recommends the best time to apply for the best result. Some products will give you season-long control of lawn weeds while others provide short-term solutions and probably spaced-out applications.

Barricade can even be applied in the fall for crabgrass control the next season. Dimension can be applied as early as March 1.” – Kansas City

If you are not very experienced at caring for your turf, I would recommend that you try these long-term solutions for preventing and getting rid of unwanted weed grasses in your lawn.

Types of Pre-emergents

When to apply crabgrass preventer or preemergent

So far, we can categorize these herbicides as short and long-residual preventers. Your current problem and level of experience may determine which one you should choose as a pre-emergent solution. I have a full review breakdown of different Pre-Emergent products here.

The Best Short residual pre-emergent

These usually last for about 60 days after application. Though the best time to apply may depend on the weather pattern, the actual best time to apply crabgrass preventers with short-lived effectiveness should be around mid-April.

Examples of short residual pre-emergents on the market today include Scotts Halts, Team, and Tupersan Crabgrass Control. I personally like the Scotts Halts product listed below…

Affiliate links and images pulled from the Amazon Product Advertising API on: 2024-06-11

The Best Long-term residual preventers

If you have no idea how to time the application of a grass weed preventer, I would recommend you go with the long-term solutions.

A single application of these herbicides will rid your lawn of crabgrass throughout the season.

The best examples include Snapshot and Dimension. You can apply any one of these earlier than the timing of the short-term options. The effect will last throughout the season.

If you need just one suggestion to go with after doing all the research, I would highly recommend Snapshot listed below…

DOW Snapshot 2.5 TG Granular Pre-emergent Herbicide
  • Snapshot 2.5 boasts more control than any other pre-emergent herbicide on the market
  • Up to 6-8 months of control for 111 broadleaf and grassy weeds
  • Application rate: 2.3 to 4.6 lb per 1000 square feet

Affiliate links and images pulled from the Amazon Product Advertising API on: 2024-06-11

Crabgrass Control Before Germination

Your timing needs to be perfect for the best results. Here are tips to help you with the timing.

  • Take and track the soil temperature of your lawn. The best time to apply a crabgrass pre-emergent is just before the rain when the temperature is between 50 and 55°F.
  • You can observe dogwoods or forsythia and use them as an indicator. In this case, start the crabgrass control measures just before the dogwoods begin to bloom.

Is It Too Late to Put Crabgrass Preventer?

Trying to kill crabgrass can be a waste of effort if you put down the crabgrass killer at the wrong time. When killing crabgrass, remember timing is everything.

Getting back to the big question is it too late to kill crabgrass, the answer is no if done in the early spring because this is the right time to apply crabgrass emergent to greatly reduce crabgrass growth.

Since crabgrass emergents work by creating a barrier to kill the weed seeds, while they are germinating, it makes sense to apply crabgrass killers before the seeds germinate.

As a thumb rule, stick to April 20th to lay down the first round of a crabgrass preventer. It is too late to kill crabgrass with a pre-emergent in the late spring because the time to apply a pre-emergent has come and gone.

However, you can apply a crabgrass post-emergent herbicide in early to late spring, which is when the weeds are small and actively growing and, therefore are in a better position to absorb the weed killer.

How to Apply Crabgrass Preventers

When applying crabgrass preventers, there’s a right and wrong way and you can use either a lawn spreader or garden seeder for the task.

You can follow the steps below to apply a crabgrass preventer but it’s important to follow the instructions on the manufacturer’s label.

However, there are a few things to keep in mind before putting down a crabgrass herbicide:

  1. Apply the crabgrass herbicide uniformly across your lawn and make sure you don’t miss any spots whether it’s a liquid crabgrass preventer or granular crabgrass preventer
  2. After application, water your lawn consistently to activate the crabgrass herbicide
  3. If you have a newly seeded lawn or have overseeded certain areas, wait until you’ve mowed the lawn a few times before application
  4. Avoid applying a crabgrass preventer or any other type of herbicide on windy days and around bodies of water
  5. Make sure you apply any chemicals when kids and pets aren’t around
  6. Lastly, avoid overstocking herbicide and store it in a safe place

Tips to Applying Crabgrass Preventers

  • Make sure the sprayer or spreader is in good working condition
  • Wear protective gear such as safety glasses, gloves, a hat, a long-sleeved shirt, and long pants
  • Calibrate the sprayer or spreader
  • Load the sprayer or spreader with the right amount of crabgrass preventer product
  • Target the weeds you want to eliminate and do not spray the product all over the place
  • When broadcast spraying, make sure you’re not leaving any treated strips
  • Spray at a height of roughly 2 feet above the grass to ensure optimal coverage
  • Clean your sprayer or spreader thoroughly after application

Types of Crabgrass Preventers

Liquid

Liquid crabgrass control products are a go-to choice for most professional lawn care service providers for several reasons, starting with their ability to not just crabgrass but a wide variety of weeds quickly and effectively.

Research from the Purdue University Turfgrass Science states that liquid herbicides tend to be much more successful than their granular counterparts because this type of product sticks to the surface of the weed’s leaf without relying on additional moisture. Even after drying, liquid herbicides stay on the weed’s leaf even if rainfall occurs.

Granular

There are a few lawn care professionals who prefer using granular crabgrass preventers, mainly because they feel it’s faster and quicker to apply. However, just like any other product, granular crabgrass herbicides aren’t perfect and the first downside is that they have to be applied to a wet lawn for them to stick to the weeds.

This means that you either have to apply them in the early morning when your lawn is damp with dew, after rainfall or have to manually water them in. Furthermore, granular weed killers must adhere to the crabgrass for 48 – 72 hours to be effective, meaning there should be no rain in the forecast for the next several days.

Synthetic Herbicide

Even though organic herbicides are better for the environment and are safer to use, synthetic herbicides offer quicker results and are much more effective. Synthetic crabgrass killers are what you’ll find on most shelves and are a mixture of chemicals that kill a wide range of weeds including crabgrass.

However, because they are created in a lab, there are a lot of health concerns revolving around synthetic herbicides. On a brighter note, synthetic herbicides are more effective than their organic counterparts, there’s no precise mixing of household items, and there are countless options available.

Organic Herbicide

The word “organic” crops up often whether it be in the world of groceries, or organic foods fed to animals but organic weed control isn’t the same as walking into your local Whole Foods and grabbing organic burgers.

Let me explain – organic in the weed control space is a lightly regulated term that usually means a natural solution. Instead of using a synthetic herbicide created in a lab, you use a natural product that has a similar impact as a chemical.

Novice gardeners often feel organic herbicides are safer than chemicals and while this may be partly true, there’s no shortage of highly toxic organic lawn care products in the market.

Organic weed control products offer limited effectiveness, prove handy for several tasks around your home, and are often cheaper than synthetics. Some of the cons of organic crabgrass preventers include a false sense of security and generally nonselective.

Selective Herbicide

This type of herbicide will kill crabgrass only and not the grass and plants in the surrounding area. However, it’s important to read the product label to ensure that the selective herbicide kills crabgrass and other weeds you’d like to eliminate and not your favorite plants.

Non-Selective Herbicide

Just as the name suggests, non-selective herbicides will kill crabgrass, and any other plants they come in contact with. Some of the popular non-selective herbicides are Round-Up (Glyphosate) and Reward.


FAQs

Can I use pre-emergent to kill existing weeds?

can i use a pre-emergent to kill existing weeds?

It is a rule of thumb that most pre-emergent herbicides do not get rid of crabgrass and existing weeds. This goes for Scott’s Turf Builder Halts Crabgrass and Barricade – the most popular preventers.

However, Dimension can be used when crabgrass is still very young (about two leaves young).

When should I water after applying a pre-emergent?

When should I water after applying a pre-emergent?

If it does not rain a few days after application, it is a good practice to water your turf for 2 to 3 days afterward. This will wash the herbicide off the leaves into the soil where it will prevent the germination of grass weeds.

Can you apply a pre-emergent on wet grass?

Can you apply crabgrass preventer on wet grass?

When applied on wet grass, crabgrass pre-emergent will most likely stick on the leaves. Some products such as Crabgrass Barrier recommend applying it on wet grass. However, you may need to water your lawn soon after putting down the herbicide.

The reason for this is that you want the herbicide deep in the soil to prevent crabgrass from sprouting. So, if you apply on wet grass and then it fails to rain, ensure you water your lawn with a sprinkler to wash the herbicide into the soil.
Also, see our guide on “Is it ok to mow wet grass” so you can plan on the perfect time to put down a pre-emergent and when to cut it afterward.

How long do crabgrass pre-emergents last?

How long do pre emergents last

Pre-emergents last 2 to 6 months, meaning they will prevent the germination of weeds in your lawn for quite a long time.

However, not all of them are the same, so be careful not to apply a pre-emergent that might deter your grass seeds from growing.

If you already have crabgrass germinating in your lawn, use a recommended crabgrass killer such as Tenacity to destroy the grassy weed.

How often can you apply a crabgrass pre-emergent?

How often can you apply a pre emergent

Since most weed-prevention herbicides last up to 6 months, it is highly recommended that you apply twice per year.

You should allow at least 2 to 6 months between applications, and ensure that you do not apply on newly seeded lawns. Some pre-emergents can cause slow or poor germination of some grass seed species.

If you’re late, you might want to try post-emergent weed-killing options. Check out my ultimate guide on the best ways to get rid of crabgrass in your lawn here.

When Does Crabgrass Germinate?

Crabgrass typically germinates from late winter (February to mid-March) but this timeframe varies depending on temperature, rainfall, location, and from year to year. Crabgrass germinates when the soil temperature at a 2-inch depth reaches 55°F and stays at this number for at least 3 days.

Can I Apply Crabgrass Preventer in the Fall?

You can apply crabgrass preventer in the fall between late August and early October and a second application 6 – 10 weeks after the first fall application.

Can I Get Rid of Crabgrass in the Summer?

The best way to get rid of crabgrass is by applying a second application of pre-emergent herbicide in the summer.

Should I Apply Crabgrass Preventer Before or After Mowing?

If you’ve recently seeded your lawn, wait until you’ve mowed your lawn at least 3 times before spreading a crabgrass herbicide. Make sure you don’t miss a spot because crabgrass is established easily and can spread quickly to the rest of your lawn.


Final Thoughts

Although crabgrass won’t crowd around your desired grasses and is not bad for your lawn, it does look awful in the Summer.

Furthermore, this unattractive, clumpy weed will quickly take over your lawn, but applying a crabgrass preventer at the right time can stop it in its tracks.

When shopping for the best crabgrass preventer, you’ll be spoilt for choice given the sea of options available including selective and nonselective herbicides.

You’ve also got organic and synthetic herbicides to choose from where the latter tends to be more effective and quicker at their job.

The best time to apply a crabgrass preventer is in the fall and a pos-emergent after the weed is actively growing is in the summer. Applying a crabgrass preventer in the fall will prevent the weed from growing back the next summer.


References

18 thoughts on “When to Apply a Pre-Emergent Crabgrass Preventer [ Before or After Rain & Wet Grass?]”

    • As a general rule, wait at least 60 days and at least two mowings before overseeding lawn areas where crabgrass preventer was used.

      Reply
        • You can put some down now if its not below freezing on a regular basis. Waiting until after seeds germinate will harder than it has to be. Winter pre-emergent weed control treatments should be applied before the ground temperatures get above 50 degrees. Afterwards you’ll be combating the germinated seeds.

          Reply
  1. It doesn’t grow thick in shady areas. It would also need plenty of soil moisture to keep it actively growing when crabgrass season has begun.

    Reply
    • That’s true Renee, thanks for mentioning it. It still grows which can be a hindrance, so best to get it under control wherever you see it pop up.

      Reply
  2. Crab grass preventer AND over seeding info both advise early Spring. I’m confused because I assume the crab grass preventer would kill the grass seed. HELP !!!!

    Reply
    • HI Eleanor, I need to update the info and make it more clearer. As a general rule, wait at least 60 days and at least two mowings before overseeding lawn areas where crabgrass preventer was used.

      Reply
    • I would wait around 30 days for those or just do Scott’s crabgrass control and then just a straight up fertilizer without any weed prevention.

      Reply
    • Hi Linda, yes most likely it will grow back. Crabgrass is a nasty little bugger so best to get all of it out of there and then to use pre-emergents in the spring and fall.

      Reply
  3. I live in the middle AZ, and starting January 2020 and still ongoing, we set the new record for the hottest and dryest year in AZ history. We’ve had more +110° days and less rainfall (less than 1/2″) than Arizona has ever seen, and while spring 2019 was the coldest & wettest spring on record, this year, unfortunately, has virtually zero rainfall expected. I bought my property about 4 years ago, and it was beyond overrun with crabgrass. Literally every inch of my yard (bare ground made mostly of caliche clay except for my 2 pine trees) has a mature network of crabgrass roots that seem like they’re all connected to each other. I have pinched nerves in my back several times and actually developed “tennis elbow” trying to eradicate this devil of a weed as the only thing that seems to make any progress is digging up as much of the roots as I can, by hand. I thought I might have gotten the upper hand this year, finally, but I noticed new green shoots already in various areas of my yard. The ground is not yet 55°, as it gets into the upper 30s to mid 40s at night still, but if I’m already seeing fresh growth, would you recommend putting down a pre-emergent now? I saw that you mentioned the option for a type that can be applied in the winter, could that possibly be an option to use now? Our rainfall happens out of the blue usually, and in 2 years hasn’t even gotten the ground wet enough to effectively soak granules into the ground, so I’d definitely have to water my “dirt” after application. I’m not worried about “lawn safe” products, as the only thing green in my yard is grassy and broadleaf weeds, but I don’t want to use something that could kill my pine trees, as the shade they provide keeps my house about 20° cooler during summer. Any help or suggestions you might have would be greatly appreciated, I’m at my wits end and can’t keep wrecking my body for as little progress as I’ve made. =(

    Reply

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