When to Use Pre-Emergent Weed Killer

Pre-emergent is a preventive weed control solution that can kill weeds before they start to take over your lawn. By applying pre-emergent weed killer at the right time of the year and following proper application methods, homeowners can enjoy a beautiful green lawn throughout the growing season.

Understanding the different products, how they work, and knowing when to use pre-emergent weed killer depending on the season and region is crucial to taking care of your lawn and managing your pre-emergent weed control. In this article, we’ll discuss what pre-emergent is, how it works, how to apply it, and when to use pre-emergent weed killer.

Let’s get to the root of it!

What Is Pre-Emergent Weed Killer?

Pre-emergent weed killer is a type of herbicide designed to prevent weeds from germinating and growing by targeting them before they emerge from the soil. It creates a soil barrier that stops weed seeds from growing healthy root systems, effectively stunting their growth and eliminating the invasive weed's ability to propagate further. By starting lawn care with pre-emergent weed killer instead of waiting to kill full-grown weeds, homeowners can more easily protect the grass from blemishes and competing plants.

Pre-Emergent Weed Killer vs. Pre-Emergent Herbicide

Both pre-emergent weed killers and pre-emergent herbicides are useful options for protecting lawns. However, homeowners must choose the right one based on grass types and the types of weeds in their lawn. Because the two terms are often used interchangeably, researching specific products and solutions is best.

Differences: Prevention vs. Elimination

Both chemicals kill or weaken weeds before they become established. However, pre-emergent weed killers target specific types of weeds and stop them from developing root systems. Herbicides prevent the seeds of weeds like broadleaf weeds from germinating in the first place, preventing cell division and killing the seedlings. Both methods can effectively clear well-maintained lawns from invasive weeds.

Choosing the Right Product

To choose the right product, homeowners should assess their lawns and identify which types of weeds are present. Then, they can look up whether pre-emergent weed killers or herbicides are the most effective choice for each type of weed. Every lawn is different, so it can also help to consult with a local landscaping company.

How Pre-Emergent Weed Killer Works

Pre-emergent weed-killer works by preventing specific types of harmful weeds and grasses from growing and absorbing vital nutrients meant for your grass. Pre-emergent slowly sinks into the top layer of a lawn's soil, coating the weed seeds. When the weeds start to grow, the active ingredients interfere with the weed’s ability to grow adequate roots.

With a limited ability to absorb water and nutrients, the weeds are weak and will be pushed out by nearby grasses and plants before they can propagate. However, pre-emergents are typically an annual requirement; lawns can get repopulated with weed seeds carried by the wind or squirrels and other pests.

Types of Weeds Controlled

There are two broad classes of pre-emergent weed killers: selective options, which target specific weeds and can be used across lawns and garden beds, and non-selective chemicals, which can kill adjacent grasses and seedlings if they aren't carefully applied.

Selective pre-emergents often target weed like:

Chickweed
Crabgrass
Goosegrass
Spurge
Crabgrass
Tall fescue
Dandelions
Nutsedge
Annual bluegrass — or Poa annua

Pre-emergent weed killers are most often used to eliminate annual weeds and certain types of annual grasses. In fact, they’re so effective at getting rid of crabgrass and preventing further weed growth, that they’ve earned the title, “crabgrass preventers”.

Homeowners can find selective weed killers that target either grassy weeds or broadleaf weeds endemic to their area, but there is no one chemical that can target all weeds without jeopardizing other plant growth. Speak with your local lawn care professional to learn about the best type of pre-emergent to manage weed growth in your lawn.

Application Methods

There are also two different application methods that landscaping companies or homeowners can choose between: granular pre-emergents, which are small, solid pieces of weed killer that can be sprinkled across the area, or liquid pre-emergents, which are mixed together and then sprayed on the ground.

The pros of granular pre-emergents are:

Easier handling
Can be more quickly applied to large areas
Excess material is easy to store and use next season

The pros of liquid pre-emergents are:

Better for even and precise applications in specific areas
They seep into the ground faster

How to Apply Pre-Emergent Weed Killer

While homeowners can apply pre-emergent weed treatments, this is only one piece of a large weed control puzzle. It's important to maintain a multi-faceted approach to controlling weeds before, during, and after the growing season. That's why many homeowners and commercial properties turn to professional weed control services that can manage the timelines and guarantee better results.

DIY Application

Homeowners can apply their own pre-emergents by following these steps:

Identifying the weeds that are common in their neighborhood or which grow frequently on their lawn
Choosing the right type of pre-emergent chemical and application method and purchasing it from a reputable source
Protecting themselves with a long-sleeved shirt, gloves, and a face mask before application
Physically applying the pre-emergent:
- Granules can be applied with a walk-behind or push spread across an entire lawn. This process requires two passes and manual application along the edges.
- Liquid pre-emergent weed-killer must be diluted with water to achieve the right concentration, poured into a sprayer, and applied evenly across the entire area you want to protect. It's generally recommended to use a grid pattern so the lawn is evenly covered. After application, homeowners must also water the lawn to encourage absorption.

a lawncare professional deploying pre-emergent weed killer

When to Hire a Professional

While DIY options are available, there are many advantages to hiring professional landscaping services and pre-emergent weed killer services, especially if you have a large lawn. Professionals can better identify specific weeds and match your lawn with the right chemicals. They also have the tools and experience to evenly cover your lawn, address specific weed infestations, and time the applications properly for your area.

When to Apply Pre-Emergent Weed Killer

Most lawns with an established root system should be treated twice a year: a fall and spring application.

However, it’s not recommended to use pre-emergent in the same season you overseed, install new sod, or plant grass seeds. Pre-emergent weed killer is meant to prevent harmful roots from taking hold — but it may unintentionally prevent new grass from growing or kill your newly planted seed.

When overseeding your lawn or planting new grass seed, you should wait at least 6 to 8 weeks before applying pre-emergent weed killer. If you’ve already applied pre-emergent, you should wait a minimum of 3 months before seeding. This may vary based on your region — you may need to wait even longer to protect the health of your new grass.

Seasonal Considerations

Pre-emergents must be applied to weed seeds before they germinate and start to grow, otherwise they won't be effective. So, it's important to apply the chemicals at the right time based on your region's growing seasons, common weed types, and ongoing weed prevention programs. In most regions, pre-emergents are applied in the early spring and in late fall.

Regional Application Timelines

For a weed-free lawn, prevention is key. And while every area is different, most states need two applications of pre-emergent weed killer: in the spring and in the fall. Find your state below for an approximate timeline of when to apply the weed killer.

Colorado: Early spring (March to April) and fall (September to October)
Florida: Late winter (January to February) and early fall (September)
Georgia: Early spring (February to March) and fall (September to October)
Indiana: Early spring (March to April) and fall (September)
Iowa: Early spring (March to April) and fall (September)
Kansas: Early spring (March) and fall (September)
Kentucky: Early spring (March) and fall (September to October)
Michigan: Early spring (April) and fall (September)
Nebraska: Early spring (March to April) and fall (September)
New Jersey: Early spring (March to April) and fall (September)
North Carolina: Early spring (February to March) and fall (September to October)
North Dakota: Early spring (April) and fall (September)
Oklahoma: Early spring (February to March) and fall (September)
South Carolina: Early spring (February to March) and fall (September)
Tennessee: Early spring (March) and fall (September to October)
Texas: Late winter (February) and early fall (September)

If you’re in a region that gets heavy snow or harsh winters, check out our guide on how to winterize your lawn. Or, if you simply want more essential lawn care tips for beginners, we’ve got you covered. Contact Heroes Lawn Care to speak with a lawn care professional.

FAQs: Pre-Emergent Weed Killer

Can Pre-Emergent Be Applied After Weeds Have Emerged?

Pre-emergents are only effective if they coat weed seeds before the seeds germinate or start to grow roots. If the weeds are already present, it's time to turn to post-emergent herbicides, manual weed-pulling, or contact a local weed control service.

Does Pre-Emergent Harm Existing Grass or Plants?

Selective pre-emergents do not harm grass and plants outside of the limited number of weeds they target. However, non-selective herbicides can hurt other plants and require more precision applications.

How Often Should I Apply Pre-Emergent Herbicides?

For most lawns, prepare for two pre-emergent applications. One should be in early spring, and the second should be at the beginning of fall.

What Happens If It Rains After Applying Pre-Emergent?

Light and moderate rain can help pre-emergents saturate the soil, making the products more effective. This is particularly true of granular pre-emergent herbicide applications.

Use Pre-Emergent Weed Killer for Effective Weed Control

Pre-emergent weed killer products are a vital dimension of comprehensive weed control. To cultivate a healthy lawn, prepare for the right pre-emergent application for your region or contact a local weed control expert that can manage the entire process for you.

At Heroes Lawn Care, we provide expert advice, convenient weed control, lawn aeration, lawn fertilization services, and comprehensive lawn care. Find a local lawn care professional near you to schedule a consultation and get your weed control program settled for the season.