Are you tired of pulling pesky weeds out of your lawn? Luckily for you, pre-emergent herbicides stop unwanted plants before they sprout out of the dirt.

Timing is the key to preventing weeds with pre-emergents. Apply it in the spring when soil temperatures reach 50 to 55 degrees to stop summer weeds. For winter weeds, spread pre-emergent weed killer in fall when the soil temps fall below 70 degrees. Remember to distribute your herbicide evenly over the area you want to protect from weeds, then water it into the dirt within three to five days.

Following the steps above, you can prevent weeds from invading your yard. For more detailed instructions on using pre-emergent weed killers, keep reading this article.

You might also be interested in reading my two articles “American Cockroach Information” and “Can I Do My Own Pest Control?“

What are Pre-Emergent Herbicides?

Pre-emergent herbicides prevent weed roots and shoots from establishing themselves in the soil. Instead of killing the seeds before germination, they interrupt their growth cycle, which stops them from popping up where you don’t want them.

Pre-emergents often stop the seed’s growth cycle during the cell division and elongation stages. This fact means timing the application of pre-emergent weed killers is critical to its functioning.

Above all, pre-emergents are used to control weeds in lawns. They can also be used in the agricultural industry to stop unwanted seeds from harming cash crops.

When to Apply Pre-Emergent Weed Killer

For pre-emergents to be effective, they must be applied in the right conditions. Put the weed stopper onto the area you want to protect from weed seeds when they are ready to sprout.

For this reason, the soil temperature is the most important indicator of when to apply pre-emergent weed killer. Going further, different seasons and different target weeds require their own applications.

You can take soil temperatures yourself with a garden thermometer available from most home improvement or garden stores. As a substitute, a meat thermometer with a three-inch probe works.

Applying Pre-Emergents in Spring

You can target summer weeds with a pre-emergent application in the spring when the soil warms up to 50 to 55 degrees. The time of the year to reach this point will depend on your location and the weather in individual years.

Soil temperature readings can be found online from the National Weather Service. For the most accurate results for your yard, head outside and stick a thermometer into the ground.

The soil temperature should remain above 50 degrees for at least 48 hours. In other words, if the soil warms up for a day, then a frost cools it down, wait to apply the weed killer until the soil warms up again.

Fall Applications

A fall application of pre-emergent weed killer stops winter-germinating weeds from invading your lawn. Contrary to spring applications, you’re looking for soil temperatures to fall below 70 degrees.

Wait For A Good Weather Forecast

Besides temperature, you also want to watch out for the rain in the forecast. Too much rain before or after weed killer application could dilute the product and it won’t work as well.

For example, the best spring weather could be a few dry, warm days followed by a single day of rain. Then, apply the product just before it rains and the water will activate it for you.

How to Apply Pre-Emergent 

First, measure your lawn to determine the square footage. Then, you can buy the right amount of weed killer for your needs.

You can buy your product from a home improvement, garden or online store. They come in liquid or granular form, and the choice is up to you which one you want to use.

No matter which type you choose, the pre-emergent weed killer will need a thorough watering 3-5 days after application to activate.

Applying Granular Pre-Emergents

1. First, you’ll need a hand-held or wheeled spreader.
2. Always read the instructions on the weed killer’s label. 
3. Calibrate your spreader’s opening following the label recommendations 
4. Fill the spreader with granules.
5. Finally, apply the granular pre-emergent as evenly as possible over the entire area you want to protect from weeds.

Applying a Liquid Pre-Emergent

1. A garden sprayer helps to apply liquid weed killer, which might come with the product or be sold separately. 
2. Again, make sure you read the instructions on the pre-emergent carefully.
3. Next, mix the product following the instructions. An incorrect mixture could damage your lawn.
4. Lastly, systematically spray the weed killer row by row to cover your grass.

Choosing The Correct Pre-Emergent

Many pre-emergents are available. There are a few features that might make one the best fit for your lawn.

Selective vs. Nonselective

• Selective – Stops specific weed types while not damaging other plants.
• Nonselective – Interrupts the life cycle of every seed it touches, including grass, flowers, and vegetables. It’s effective, but be cautious to only apply it where you want it.

Selective weed killers are the most common types you’ll find at the store. Be sure to look at the label and see if it is one or the other before buying.

Which Weeds Does It Prevent?

You can choose a selective weed stopper to kill certain weeds you know cause problems in your yard. In many cases, the weed a pre-emergent weed killer targets might be on the label. Alternatively, read the active ingredients list to see which species it is most effective for.

Moreover, there are several different pre-emergent chemicals to look for in a weed killer, including:

• Simazine, oxyflourfen and isoxaben target broadleaf weeds and are ineffective for invasive grasses. 
• Dinotroaniline, napropamide, metolachlor and dicklobenil kill invasive grasses and some broadleaf weeds.
• Prodiamine stops around 30 grassy and broadleaf weeds, including annual bluegrass and crabgrass.
• Oryzalin is effective at stopping broadleaf weeds, including spurge. It’s popular for well-established, warm-season lawns.
• Dithiopyr works to stop about 45 grassy and broadleaf weeds. It has some effectiveness against already-sprouted weeds.

Broadleaf vs. Grassy Weeds

Knowing the difference between a broadleaf and a grassy weed helps you choose the best pre-emergent. Fortunately, identifying the two types can be simple if you look at them closely.

First off, broadleaf weeds have a vein in the center of their leaves with smaller veins branching out. Some common broadleaf weeds in yards around the country are:

• Dandelion
• Plantain
• Chickweed
• Prostrate Knotweed
• Ground Ivy
• White Clover
• Yellow woodsorrel
• Prostrate spurge
• Curly Dock

On the other hand, grassy weeds have long, narrow leaves with parallel veins. Also, look for visible joints where the leaves attach to the stalk. Furthermore, the most common grassy weeds in North America include:

• Annual Bluegrass
• Bermudagrass 
• Nimblewill
• Wild fescue
• Quackgrass
• Crabgrass
• Barnyard grass
• Millet

Pre-Emergent Weed Killer: Liquid or Granular 

Starting off, the two styles of pre-emergent weed preventers might contain identical ingredients. The choice normally comes down to which type you’re more comfortable handling.

Liquid Pre-emergent

• Requires careful mixing before application.
• Liquid weed stopper might be easier for some people to spread and goes on more evenly.
• The sprayer might allow some drops to drift where you don’t want them.

Granular pre-emergents

• Requires more watering for activation after application than liquid versions.
• Can be simpler to learn to apply, and it’s easier to tell where it has been applied. But, the application might take longer.
• Typically cheaper than liquid pre-emergents.

Above all, both types must be applied thoroughly and evenly. A sloppy spreading could make the product less effective.

Are Pre-Emergents Safe?

Yes, modern pre-emergent weed stoppers are safe for humans, pets and established plants when used correctly. In the end, these chemicals have been in use for decades. Over the years, multiple studies have proven them to be safe for human health and the environment.

Of course, it’s important to keep weed killers away from children, pets and areas you don’t want to kill seeds. Moreover, following the directions on the pre-emergent label will ensure your safety.

In fact, specially designed pre-emergent weed killers can be used in a vegetable garden. On that note, products containing trifluralin as the top ingredient are the best for safe use around veggie patches.

Pre-Emergent Weed Killer For Flower Beds

Flower beds benefit pre-emergent weed killers. In the case of flower beds, be sure to check the label and see that it is effective against the problem weeds in your area.

Wait to use pre-emergents until after your flowers have established themselves. On the contrary, adding pre-emergent too soon could kill the flower seeds along with the weeds.

Are There Organic Or Natural Pre-Emergents?

Yes, corn gluten extract works as a natural, chemical-free pre-emergent. You may find products containing corn gluten, or you can find the raw material to use.

Like with chemical pre-emergents, spread an even layer of corn gluten extract on your lawn or other areas you want to prevent weed growth. Then, water it into the soil and let it work.

How Long Do Pre-Emergents Work?

Overall, many pre-emergents work for about three to five months. The label on the weed killer you choose will tell you exactly how long you can expect it to last.

Weather conditions can affect the longevity of your pre-emergent. Extra rain could wash out the weed killer and stop it from working.

Most folks find that one application in the spring and one in the fall is the best recipe to prevent weeds year-round. It might take a few seasons of use to find the best schedule for pre-emergent applications for your property.