What Are Pre-emergent Herbicides and When You Should Apply Them?

A pre-emergent herbicide is a proactive weed control solution. It is applied to lawns before weed seeds germinate. It forms a barrier in the soil, preventing weed seedlings from emerging and establishing. Pre-emergent herbicides should be applied before the expected germination period of target weeds. Typically, this occurs in early spring or fall, depending on the region and the weed species. By applying pre-emergent herbicides at the right time, homeowners can effectively thwart weed growth, promoting a healthier and more vibrant lawn.

In this guide, we will detail how pre-emergent weedkillers work and how and when you should apply them. Join us in understanding how they can be a game-changer in the quest for a weed-free lawn. 

Understanding Pre-emergent Herbicides

Pre-emergent herbicides are the silent guardians of your lawn, acting as a preemptive strike against weeds before they rear their ugly heads. These specialized chemicals work by forming a protective barrier in the soil, inhibiting the germination and growth of weed seeds. Understanding the mechanisms behind pre-emergent herbicides is crucial for unlocking their full potential in maintaining a weed-free lawn.

These formulations disrupt the cellular division process in germinating weed seeds, impeding their ability to sprout and establish roots. This preventive action not only curtails the current weed population but also hinders the development of future generations.


Related Reading: Understanding Herbicide Types and Their Applications


The Weed Life Cycle

From seed germination to maturity and eventual reproduction, weeds undergo distinct stages. By gaining insight into these phases, you can pinpoint the opportune moment to deploy pre-emergent herbicides.

Timing is Everything

The efficacy of pre-emergent herbicides hinges on precise timing. Application should align with the germination period of target weeds. Understanding when weeds are most vulnerable allows you to disrupt their life cycle before they become a visible nuisance in your lawn.

Maximizing Impact

By synchronizing pre-emergent herbicide application with specific stages in the weed life cycle, you not only tackle existing threats but also prevent the emergence of new ones. This strategic approach ensures a more resilient and enduring defense against weeds, contributing to the long-term health of your lawn.

Common Weeds Controlled by Pre-emergent Herbicides

In the ongoing battle for a pristine lawn, recognizing the enemy is half the victory. With their relentless invasion, common weeds can jeopardize the health and aesthetics of your green space. Here, we shed light on some notorious culprits that pre-emergent herbicides are specifically formulated to control:

Dandelions (Taraxacum officinale)

Dandelions (Taraxacum officinale)

Dandelions, with their distinctive yellow flowers, are not just a visual nuisance but can quickly spread and overtake your lawn. To specifically address dandelions with pre-emergent herbicides, the best time for application is just before or during their germination window. This means applying the pre-emergent herbicide in early spring before the dandelion seeds have the opportunity to sprout and establish themselves in the lawn.

Crabgrass (Digitaria spp.)

Crabgrass (Digitaria spp.)

Crabgrass is a formidable foe known for its rapid growth and ability to thrive in challenging conditions. Crabgrass seeds typically begin to germinate when soil temperatures consistently reach around 55 to 60 degrees Fahrenheit (approximately 13 to 16 degrees Celsius).

In many regions, crabgrass germination occurs when soil temperatures are conducive, often in late spring or early summer. This is when the soil has warmed sufficiently for the seeds to initiate germination.

Broadleaf Weeds (Various Species)

Broadleaf Weeds (Various Species)

From clover to thistle, broadleaf weeds are a diverse group that can mar the uniformity of your lawn. They can have varying germination times based on the specific species and environmental conditions.

Many broadleaf weeds tend to germinate in the spring when soil temperatures begin to rise. As the soil warms up after winter, it provides favorable conditions for the germination of seeds. However, certain weeds may continue germinating throughout the growing season, influenced by factors like soil disturbance, temperature fluctuations, and moisture availability.

Annual Bluegrass (Poa annua)

Annual Bluegrass (Poa annua)

This cool-season grassy weed can create unsightly patches in lawns. Poa annua is a cool-season grassy weed that typically germinates in the fall or early spring.

In many regions, Poa annua primarily germinates in the fall when soil temperatures are cooler and more conducive to the germination of cool-season grasses. Poa annua may continue its growth during the winter in milder climates following fall germination. This winter growth can contribute to forming seedheads, which produce seeds that lead to new plants in the following growing season.

Poa annua can also germinate in the spring. Spring germination typically occurs when soil temperatures rise, providing a secondary window for the weed to establish itself.


Related: How to Get Rid of Poa Annua (Annual Bluegrass) In Your Lawn


When to Apply Pre-emergent Herbicides

Timing is paramount when it comes to applying pre-emergent herbicides. Understanding the seasonal dynamics of weed germination is crucial for a successful defense. 

Spring Application

For many regions, early spring marks the onset of weed germination. Applying pre-emergent herbicides during this period creates a barrier that halts weed seeds in their tracks, preventing them from sprouting and establishing roots. Spring application is particularly effective against summer annual weeds. Apply spring pre-emergent when average soil temperatures are in low 50s trending warmer. Warm-season weeds begin germinating as average soil temperatures reach the mid-50s, so you’ll want to apply your spring pre-emergent before then.

Fall Application

In some climates, fall application of pre-emergent herbicides is equally vital. This strategy addresses winter annual weeds, ensuring your lawn remains resilient through the colder months. Applying herbicides in the fall thwarts the germination of weeds that would otherwise emerge during the following spring. Apply fall pre-emergent when average soil temperatures are in the low 70s, trending cooler.  Cool-season weeds begin germinating as average soil temperatures reach the mid-60s, so you’ll want to apply your fall pre-emergent before then.

Factors Affecting Timing

Beyond the calendar, several factors influence the ideal timing for pre-emergent herbicide application. Soil temperature, moisture levels, and the specific weed species in your area all play pivotal roles. Understanding these factors empowers you to fine-tune your application schedule for maximum efficacy.

Soil Temperature

Weed seeds germinate in response to soil temperature. Monitoring soil temperature helps determine when the conditions are conducive to germination, allowing you to apply pre-emergent herbicides at the most opportune moment.

We recommend applying spring pre-emergent before average soil temperatures reach 55 degrees. Once soil temperatures are in the high 40s - low 50s and trending warmer, get your pre-emergent down.

Apply fall pre-emergent when average soil temperatures are in the low 70s, trending cooler.  Cool-season weeds begin germinating as average soil temperatures reach the mid-60s, so you’ll want to apply your fall pre-emergent before then.

Moisture Levels

Adequate moisture is essential for herbicide activation. Timing your application to coincide with anticipated rainfall or irrigation ensures that the herbicide forms a protective barrier in the soil, optimizing its weed-preventing capabilities. Pre-emergent requires ¼ - ½” of water for proper activation.


Related: What Types of Weeds Look Like Grass?


Application Techniques

Application Techniques

Applying pre-emergent herbicides requires a strategic approach to ensure even coverage and maximum effectiveness. 

Granular Application

Granular pre-emergent herbicides come in pellet form, making them convenient for spreading with a broadcast spreader. This user-friendly method allows for a relatively even distribution over large lawn areas. Granules are often recommended for homeowners who prefer simplicity and ease of application.

Liquid Application

Liquid pre-emergent herbicides are typically mixed with water and applied using a sprayer. This method offers greater precision in targeting specific areas, making it suitable for smaller lawns or irregular-shaped areas. Liquid applications can be advantageous when a more targeted approach is necessary.

Consider Weather Conditions

Choose a calm day with minimal wind for application to prevent herbicide drift. Additionally, check the weather forecast to ensure no rainfall is expected immediately after application, allowing the herbicide to adhere to the soil.


Related: How to Get Rid of Weeds — Everything You Need to Know


Tailoring Pre-emergent Herbicides to Weed Species

When it comes to pre-emergent herbicides, one size does not fit all. Different weeds require specific formulations for effective control. Pre-emergent herbicides are selective, meaning they may be more effective against certain weed types while sparing desirable turf grass. For instance, a herbicide formulated to control crabgrass might be less effective against broadleaf weeds. Understanding this selectivity ensures you choose a product tailored to the weed species threatening your lawn.

Specticle FLO

Specticle Flo is a liquid pre-emergent weed killer for warm-season grass that should be used only on warm-season grasses. It controls more than 60 types of weeds, including clover, dandelions, sowthistle, spurge, chickweed, annual sedges, crabgrass, Poa annua, foxtail, and more.

To apply this pre-emergent herbicide, you will need a 4-gallon sprayer with a large droplet nozzle.  It is best used in late summer or early fall to prevent weeds from germinating in the spring. The great thing about this weed killer is that it only needs to be applied once in the fall for excellent control of fall and late winter weeds.

Specticle FLO

Prodiamine 65 WDG

Prodiamine 65 WDG is a water-dispersable granule pre-emergent that controls grassy and broadleaf weeds. It makes quick work of preventing Poa annua germination in the fall, crabgrass in the spring, and over 30 more weeds. It can be used on cool and warm-season lawns.

You’ll need a backpack sprayer for this herbicide, as you will mix it with water to create a liquid. It does need to be watered in after application. For best results in the fall, apply prodiamine in September and again in December.


Dithiopyr 0-0-7 Pre-emergent with Fertilizer

Dithiopyr 0-0-7 is a pre-emergent herbicide combined with fertilizer that is great for use on both warm and cool-season lawns as it won’t kill your grass. It is particularly effective at controlling dandelions and crabgrass.

As it is mixed with a fertilizer, it has to be applied using a broadcast spreader. It should be used on a dry lawn and watered in with rainfall or irrigation within 48 hours of application. This pre-emergent is best applied when soil temperatures are below 55F in spring. In the fall, apply when soil temperatures are in the low 70s.  Fall or spring pre-emergent applications provide around four months of protection against weeds while fertilizing your lawn.

Dithiopyr 0-0-7 Pre-emergent with Fertilizer

Prodiamine 0-0-7 Pre-emergent with Fertilizer

Prodiamine 0-0-7 pre-emergent with fertilizer is a granular version of the herbicide mixed with a fertilizer. It also contains 7% potassium, so it is a great weed and feed product suitable for all grass types without the risk of it killing your lawn.

It will control many broadleaf and grassy weeds, but it primarily controls Poa annua and crabgrass. Like dithiopyr 0-0-7, it should be applied to a dry lawn and watered into turf within 48 hours with 1/4" of irrigation or rainfall.

Prodiamine 0-0-7 Pre-emergent with Fertilizer

Benefits of Using Pre-emergent Herbicides

Pre-emergent herbicides offer a proactive approach to weed management, preventing weed seeds from germinating and establishing. By creating a barrier in the soil, these herbicides reduce competition for essential nutrients, allowing your lawn to flourish without the encumbrance of unsightly and invasive weeds.

Impact on Overall Lawn Health and Appearance

Maintaining a weed-free lawn goes beyond mere aesthetics; it directly influences the overall health of your turf. Pre-emergent herbicides contribute to a lush and vibrant lawn by curbing the growth of weeds that can otherwise stunt the development of grass and compromise the uniformity of your landscape.

Cost-Effectiveness in Long-Term Weed Management

Investing in pre-emergent herbicides proves to be a cost-effective strategy for long-term weed control. Preventing weed infestations before they become established reduces the need for expensive and time-consuming measures to combat mature weeds. This proactive approach not only saves money but also minimizes the labor-intensive tasks associated with weed removal.


Related: Best Nutsedge Weed Killers


Potential Challenges and Considerations

Limitations of Pre-emergent Herbicides

Despite their efficacy, pre-emergent herbicides have limitations. Some may not effectively control certain weed species, while others may require precise application timing. This section explores the constraints of pre-emergent herbicides, helping you make informed decisions about their use in your lawn care regimen.

Environmental Considerations and Responsible Use

Balancing the benefits of pre-emergent herbicides with environmental responsibility is paramount. Understanding the potential impact on non-target plants, water sources, and beneficial insects guides you in making environmentally conscious choices. 

Integrated Weed Management Strategies

Acknowledging that pre-emergent herbicides are one tool in the arsenal of weed management, this section advocates for an integrated approach. Incorporating cultural practices, regular lawn maintenance, and alternative weed control methods enhances the effectiveness of pre-emergent herbicides in creating a resilient and thriving lawn.

For optimal results, explore the range of pre-emergent herbicides Golf Course Lawn offers. Take the first step towards a weed-free and thriving lawn today.