How to Apply Pre-Emergent Herbicides

April showers bring May flowers — and weeds. That’s why it pays to stop weeds before they sprout in your lawn. To apply pre-emergent herbicides, grab a calculator, a spreader or sprayer, and your chosen product.

Below, you’ll find tips and detailed advice on how to apply pre-emergent herbicides, from tools to timing, which is crucial for getting the best results. Early-season weed control takes a bit of planning, but your efforts in the pre-season will save you from having to deal with a yard full of weeds later on. Let’s get started.

What is a Pre-Emergent?

A pre-emergent herbicide is a form of preventive weed control for lawns that disrupts seed growth by creating a chemical barrier in the soil. Unlike post-emergent herbicides that target visible weeds, pre-emergents target only weed seeds that haven’t germinated above soil level yet.

For pre-emergent applications to work, you have to know when to apply them, which is before weeds begin to pop up everywhere.

• In the spring, apply pre-emergent herbicides when the soil temperature is 50-55 degrees Fahrenheit.
• In the fall, apply pre-emergent herbicides when the soil temperature is 70 degrees Fahrenheit.

Applying pre-emergent herbicides too early may be ineffective. It’s possible that the herbicide will break down or wash away before it has a chance to disturb the weed’s growth and prevent it from sprouting aboveground. 

Applying too late will also be ineffective. If weeds in your lawn have already sprouted, apply a post-emergent instead.

See Related:

• What Are Pre-Emergent Herbicides?
• When to Apply Pre-Emergent Herbicide

Preparing for Pre-Emergent Application

Before you get started, there are some things you should do to prepare for a pre-emergent application. 

1. Measure Your Lawn

Calculate the square footage of your lawn by multiplying the length and width of your lawn in feet. The best pre-emergent herbicides will indicate the coverage in square feet.

To calculate the square footage of your lawn, use the following formula:

Length of Lawn (in feet) x Width of Lawn (in feet) = Square Footage of Lawn

Once you have the measurement of your lawn, you can check it against the product’s recommendation by reading the label instructions.

2. Choose a Pre-Emergent

Consider the advantages and disadvantages of each type of herbicide and choose the one that suits your preferences and needs. You may need specific equipment depending on the type of pre-emergent herbicide you choose.

• For granular herbicides, you need a spreader to distribute the product evenly. Granular herbicides take time to activate and release into the ground. They also won’t cover the area as evenly. 
• For liquid herbicides, you need a sprayer. Liquid herbicides are easier to spread in an even layer over your lawn. They are also faster-acting than granular herbicides. Typically, liquid herbicides also require product mixing.

Another important consideration is knowing which types of weeds you have, which will determine your lawn weed control method:

• Selective pre-emergent herbicides kill a certain type of weed, so they should be safe to use around other plants. So if you are wondering How to Get Rid of Crabgrass, selective pre-emergents might work best for your lawn.
• Non-selective pre-emergent herbicides cause harm to any plant they are applied to, not just weeds. These products are not used in lawns (because you don’t want to kill the grass, right?). Instead, they’re often used in products that also include a post-emergent to prevent and kill vegetation in a small area.

3. Gather the Tools You’ll Need to Apply Pre-Emergents

Regardless of the type of herbicide you are using, you will need the right tools to help you spread pre-emergents around your property.

Tools needed to apply a liquid pre-emergent:

• A weed sprayer
• Measuring cup
• Measuring tape

Note: Some liquid pre-emergent products come with a sprayer attached to the bottom that connects to your hose end and automatically dilutes the product during application. Others require mixing into your own sprayer; a handheld or backpack pump sprayer is often used.

See Related: How Much Does a Weed Sprayer Cost?

Tools needed to apply a granular pre-emergent:

• A spreader, either a manual push (similar to a wheelbarrow) or a handheld style.
• Measuring tape

See Related: Best Fertilizer Spreaders

For your safety, wear protective clothing:

• Gloves
• Long-sleeved shirt and long pants
• Protective shoes
• Eye protection
• Dust mask

Wear a dust mask and rubber gloves to prevent skin and lung irritation from the product dust when loading the spreader. Wear long pants, socks, shoes, or even rubber boots when applying to prevent irritation from any product contact.

4. Check the Weather

An herbicide for lawns should be applied when the lawn is dry. You shouldn’t apply herbicides to wet areas. So before you start, check the weather.

Also, you want to wait for a calm, still day. If it is windy outside, you should wait to apply your pre-emergent herbicides on another day.

5. Read the Product Label Carefully

By law, herbicide labels must contain specific information on the ingredients, proper application, safety precautions, and product dangers. Although it’s hardly provocative prose, read the labels thoroughly and follow their instructions.

“People just don’t read labels,” says Karey Windbiel-Rojas, a pest management specialist at the University of California. In her community outreach programs, she stresses the importance of reading and understanding labels.

How to Apply a Granular Pre-Emergent Herbicide

You will need a spreader to apply granular pre-emergent herbicide to your lawn. By following these steps, you’ll be well-prepared to effectively apply pre-emergent granules and prevent weed growth in your lawn. 

Just remember to avoid exceeding the recommended application rate. Applying too much herbicide can harm your lawn and surrounding plants. 

• Step 1: Fill your spreader. Fill your spreader with granular pre-emergent herbicide. Look at the recommendations on the label to determine the amount of herbicide product you need to apply on your lawn.
• Step 2: Set the spreader. Calibrate the spreader to match the application rate on the product label. This ensures you’re not overapplying the pre-emergent herbicide.
• Step 3: Apply the pre-emergent. Apply the granular pre-emergent by walking across your entire lawn, squeezing the handle on the spreader and spreading the granules as evenly as possible. Release the handle anywhere you don’t want to apply the product.
• Step 4: Clean your spreader. Make sure to clean your spreader out well so that no traces of chemical herbicide products remain.
• Step 5: Water your lawn. Thoroughly water your lawn to ensure the herbicide can reach the seeds in the soil. No matter which pre-emergent you choose, it will need about 1 inch of water to activate. 

Pro Tip: Cut the recommended application rate in half and go over the same area twice. Apply the product lengthwise across your yard and then crosswise to ensure even distribution.

How to Apply a Liquid Pre-Emergent Herbicide

Liquid pre-emergents are easier to spread evenly over your lawn, though the spray does tend to drift, especially on windy days. Make sure you pick a relatively calm day with little wind.

Additionally, it is essential for liquid pre-emergent weed killer spray to be mixed carefully. Pay attention to the mixing ratios, application rate, and safety precautions in the manufacturer’s instructions.

• Step 1: Measure the herbicide. Use a measuring cup or small kitchen scale to measure the herbicide accurately. Mix the herbicide with water according to the label directions. (Note: If you’re using a kitchen scale, don’t return it to the kitchen. Dedicate it for lawn care use only.)
  
  Note: Some pre-emergent herbicide products come with a sprayer that attaches to your hose. This automatically dilutes the product, thereby saving homeowners the hassle of mixing the herbicide themselves. This may be an easier option for DIYers. 
• Step 2: Apply the herbicide. Walk at a steady pace, applying the lawn weed killer evenly across your entire lawn. Ensure you overlap the spray areas slightly. Move across your yard as if you’re mowing to cover the area. Do two passes, perpendicular to each other, for thorough coverage.
  
  Pro Tip: As you apply a liquid pre-emergent, hold the nozzle close to the ground to minimize spray being blown astray. 
• Step 3: Clean the sprayer. When you are finished, thoroughly clean your sprayer with water to prevent any residue from clogging the components and affecting future applications. If needed, you can also use a mild detergent or liquid soap to clean the container.
• Step 4: Water your yard. To activate the pre-emergent herbicide, water your yard after application. It’s crucial that you don’t forget this step because your weed preventer won’t work without water. 

Pro Tip: You may want to use marker flags or another kind of marker so you remember which areas of the yard you have already treated with herbicide. This is especially helpful if you have a large yard.

Stay off the lawn for at least 24 hours, and keep pets and children away from the treated area for 24 to 48 hours (but check the label’s instructions for exact timing).

FAQ About How to Apply Pre-Emergent Herbicides

Don’t Wait to Deal With Your Weeds

As the season begins to warm up (or cool down), be ready to take preemptive action to stop weeds from growing in places where they’re not allowed. Choose a pre-emergent, gather your spreader or sprayer, and choose a windless, calm day to apply. Water it in, and you’re set for the season.

However, it can be a hassle to gather all the right equipment and time the application dates correctly. If herbicide application sounds like too much of a chore for you, hire a local lawn treatment professional who can do the job for you instead.

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