When to Apply Pre-Emergent: Complete Guide


Before weeds appear in your lawn, pre-emergent herbicides prevent their seeds from germination. Pre-emergents require precise timing, selection of the best type for your yard, and herbicide application.

Your lawn ought to stay lush, green, and weed-free when combined with post-emergent herbicides. However, you require both pre- and post-emergents. Using both kinds of weed killers will support a healthy lawn, much like bookends keep your books upright.

This article discusses the function of pre-emergent herbicides, when and how to use them, and some typical application errors.

What is Pre-Emergent Herbicide?

Pre-emergent herbicides are chemicals that are applied to your healthy lawn or flower bed to stop weeds from sprouting. This treatment slows down the development of new roots, but it does not affect the weed’s seed germination.

Types of Pre-Emergent Herbicides

There are typically two types of pre-emergent herbicides: liquid pre-emergent and granule pre-emergent. Each type has distinct qualities and ways of application, even though they are all designed to fight sprouting weeds.

Liquid pre-emergents are usually sold in pump-type sprayers or hose connections. The wide application of this pre-emergent, which evenly coats your lawn thanks to its quick flow rate, is one advantage. There are a few advantages to a granular treatment, even though many lawn care professionals favor liquid pre-emergents.

Granular pre-emergents require little to no mixing compared to their liquid counterpart, which makes preparation a little easier. Furthermore, you can apply granular pre-emergent with a lawn spreader you already have for fertilizing.

How Pre-Emergent Herbicide Works

Pre-emergent herbicides function by building a temporary wall between weed seeds and your lawn. Weeds are eliminated prior to sprouting by this barrier, which prevents them from penetrating the topsoil. Pre-emergent also lessens the likelihood of future issues by reducing seed production in addition to preventing the growth of current weeds.

When to Apply Pre-emergent Herbicides

The most important aspect of preventing weeds from sprouting up in your yard is the time of year you apply your pre-emergent herbicide. Two factors — season and ground temperature — determine when it’s the right time to apply your herbicide:

By Season

Every season, pre-emergents are used to stop the germination of weeds. A post-emergent can be used when weeds start to emerge after a pre-emergent, which typically lasts three to five months.

For example:

To avoid winter and fall weeds like bluegrass and prickly lettuce, apply a pre-emergent herbicide from August to November.

To get ahead of early spring and summer weeds, apply pre-emergent herbicides around mid-March.

By Ground Temperature

Pre-emergents should be applied at the proper time, but you also need to be aware of the ground’s temperature.

For example:

To prevent summer weeds, apply a pre-emergent herbicide once the ground temperature has been 55 degrees for at least 48 hours.

To prevent winter weeds, apply a pre-emergent herbicide in the fall when ground temperatures reach 70 degrees and continue to drop.

A thermometer should be inserted two inches below the soil surface to gauge the temperature of the ground.

How to Apply Pre-emergent Herbicides


Both the timing and method of pre-emergent herbicide application are crucial.

Applying your weed deterrent correctly requires the proper equipment, the right pre-emergent herbicide (granular or liquid, selective or non-selective), and systematic spreading or spraying of your weed killer.

Oh, and make sure to check the weather before applying your pre-emergent so that your herbicide doesn’t wash away with a summer rainstorm. Additionally, if there has been a sustained period of rain, you should wait until the ground is completely dry before applying the herbicide.

How to Apply Granular Pre-emergents

What you’ll need: A spreader, either manual push (similar to a wheelbarrow) or hand-held styles.

What to do next: Pre-emergent herbicide granules should be loaded into your spreader in accordance with the label’s recommended application rate. Adjust the spread to the size of the yard where you intend to spread the pre-emergent herbicide.

Release the handle on your equipment, walk across your entire lawn, and spread the granules as evenly as you can. To avoid an uneven application, make sure to go over the same area repeatedly without exceeding the necessary application rate.

How to Apply Liquid Pre-emergents

What you’ll need: Most liquid pre-emergent herbicides come with their own sprayer, but you can also buy a portable pressure sprayer tool, which is available in a variety of sizes and types.

What to do next: As specified on the herbicide label, combine your liquid pre-emergent with water in the recommended ratio. As you mow your lawn, evenly and in rows, spray your yard with liquid herbicide.

Apply your liquid pre-emergent uniformly.

Selective Vs. Non-selective Herbicides

If you selected a selective or non-selective herbicide, it will also affect how you spread your pre-emergent. For instance, if you selected a pre-emergent selective for crabgrass, you can spread the pre-emergent evenly over any area with that particular weed without having to worry about harming nearby grasses or plants.

You will require good hand-eye coordination and attention to detail if you select a non-selective pre-emergent. You run the risk of killing healthy, non-weedy vegetation if you use a non-selective pre-emergent, so be sure to carefully spray the area where you want to prevent weeds.

Water Your Lawn After Applying Herbicide

Pre-emergents and irrigation go hand in hand. Almost all pre-emergent herbicides, whether they be organic, synthetic, liquid, or granular, require water to function.

To make sure the herbicide gets to the seeds by moving through the soil, you should sprinkle water on the area within a short period of time (three to five days).

Pre-emergents shouldn’t be used on soggy lawns. After using your herbicide, wait until your grass is completely dry before watering your lawn.

Pro Tip: Make sure to thoroughly saturate the area with water to ensure the herbicide penetrates to the seeds. Granular pre-emergents typically require more water than liquid types.

Common Pre-emergent Application Mistakes

Uneven application: Patches of weed may appear in your yard if you apply your pre-emergent herbicide unevenly or in some areas but not others.

Applying too little or too much herbicide: If you use too little herbicide, the product won’t work, and weeds will soon start to grow there. If you use too much herbicide, it can damage the grass and other nearby plants, making it difficult to reseed the area later.

Don’t Combine Pre-emergents With Other Lawn Care

Pre-emergent application is a task that needs to be completed independently. The effectiveness of the herbicide may be hampered by recent aeration, overseeding, or fertilization of your lawn.

Additionally, if you used pre-emergent herbicides, you should wait at least a year before laying new sod there.

Kinds of Weeds Pre-emergent Herbicides Block

Knowing what weeds thrive in your yard is important for determining when to use pre-emergent herbicides to prevent weeds based on the season.

For instance, winter- and summer-appearing fescue and spurge seeds both grow quickly.

Typical summer annual and late spring grassy and broadleaf weeds include:

  • Foxtail
  • Crabgrass
  • Clover
  • Dandelions
  • Ragweed

In the winter, you might notice weeds like:

  • Bluegrass (poa annua)
  • Prickly lettuce
  • Chickweed

How to Choose the Best Pre-Emergent Herbicide

Your yard’s weed situation will determine the best pre-emergent. Here are some common chemicals in herbicides and the weeds that they target:

  • Prodiamine—On crabgrass and dandelion, this substance is frequently used. To get rid of different invasive grasses in your lawn, you can also use herbicides that contain prodiamine.
  • Oxyzalin—Even though this substance is typically used in agricultural settings, some homeowners use it to get rid of invasive vines like morning glory and yellow foxtail.
  • Dithiopyr is a substance that is used to inhibit the growth of invasive grasses and climbing plants.

It’s important to take into account the size of your lawn and how much effort you’re willing to put into treatment in addition to the types of weeds you experience. For instance, a granular pre-emergent may be a good choice if you have a small area that needs to be treated quickly. However, a liquid pre-emergent might be a good option if you want an even application over a large area and don’t mind some pre-application mixing.

Important Tips for Using Pre-Emergent Herbicide

Before applying pre-emergent weed control, consider the following application tips:

  • Apply pre-emergent evenly—You must make sure that no area of your lawn is left untouched if you want to completely protect it from weeds.
  • Don’t forget water—Water activates herbicide treatments, dispersing chemicals throughout the soil of your lawn. Apply pre-emergent before a predicted downpour to conserve water. The lawn should be watered after application even if rain is not expected.
  • Limit lawn activity—Following application, it’s critical to prevent any disturbance of the soil holding the pre-emergent. As a result, you shouldn’t aerate after application and you shouldn’t mow until after the pre-emergent has been watered.
  • Maintain your lawn—A healthy lawn can fight off common weeds on its own by being kept in good condition. Mowing, appropriate irrigation, and pest management should all be part of routine maintenance. Consider using a lawn care service like Lawnbright or TruGreen if you don’t have the time to maintain your lawn.


When it’s appropriate to apply your herbicide, two key considerations are the season and ground temperature. Additionally, choose the appropriate pre-emergent based on the weeds your yard typically has.


What Month is Best for Pre-emergent?

Apply pre-emergent herbicides around mid-March to get a head start on early spring and summer weeds.

Is April Too Late for Pre-emergent?

Preemergence weed control treatments get rid of invasive plants before they sprout. The temperatures at which various weeds germinate and spread vary. Hence, it’s never too late for preemptive treatments to work in your favor.

Is It OK If It Rains After Applying Pre-emergent?

What impact will rain have on the pre-emergent I used on my lawn? ””””’ ‘ling Many people believe that rain will wash our products away and render them useless, but this is simply untrue. Actually, rain makes our lawn treatments work much better.