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When To Apply Pre-Emergent Herbicide

Pre-emergents stop growing weeds before they’re even spotted in your lawn. Keep reading to learn more about the preventative measure, the best time to apply it, and how it can protect your lawn.

Author Icon By Stephanie Koncewicz Updated 01/07/2024

Your yard can become vulnerable to harmful diseases, insect infestations, and drought when weeds sprout. To protect your yard from damaging weeds, it’s important to incorporate an effective pre-emergent into your lawn care routine.

However, for pre-emergent to be effective, it needs to be applied at the correct time of year. In this article, we’ll detail when to apply pre-emergent herbicide, discuss application techniques, and walk you through some helpful tips for working with the product.

What Is Pre-Emergent Herbicide?

A pre-emergent herbicide is a chemical application that prevents weeds from sprouting in your healthy lawn or flower bed. While this treatment doesn’t interfere with the weed’s seed germination, it does stop growth by stunting the formation of new roots.

Types of Pre-Emergent Herbicides

Pre-emergent herbicide typically comes in two different forms: liquid pre-emergent and granule pre-emergent. While each type is structured to combat sprouting weeds, they each have unique characteristics and application methods.

Liquid pre-emergents are usually sold in pump-type sprayers or hose connections. One benefit of this pre-emergent is its widespread application, as its fast flow rate causes it to evenly coat your lawn. While many lawn care experts prefer liquid pre-emergents, there are a few benefits to a granular treatment.

Granular pre-emergents require little to no mixing compared to their liquid counterpart, which makes preparation a little easier. Additionally, if you already own a lawn spreader for fertilizing, it can be used for applying granular pre-emergent.

How Pre-Emergent Herbicide Works

Pre-emergent herbicides work by creating a makeshift barrier between germinated weeds and your lawn. This protective layer prevents weeds from breaching the topsoil, eliminating them before they can sprout. In addition to preventing existing weeds from growing, pre-emergent also reduces the chances of future problems by reducing seed production.

When To Apply Pre-Emergent Herbicide

The right time to apply your pre-emergent herbicide varies depending on the type of weeds in your lawn. For example, some weeds emerge in the fall while others, such as dandelions, grow a bit earlier in the year.

Spring applications help prevent the growth of summer weeds, such as crabgrass and foxtail. However, it’s important to hold off on applying until your summer fruits and vegetables have sprouted as pre-emergent can harm ungerminated plants.

By the time cooler weather comes around, the protection from your spring pre-emergent has diminished. Fall applications keep new weeds from growing and wreaking havoc in the spring. Consider applying this pre-emergent before soil temperatures reach 55 degrees for five or more days in a row.

How To Choose the Best Pre-Emergent Herbicide

The right pre-emergent will depend on your yard and the type of weeds it experiences. Here are some common chemicals in herbicides and the weeds that they target:

This chemical is typically used on crabgrass and dandelions. Herbicides that contain prodiamine can also be used to eliminate various invasive grasses in your lawn.
Although this chemical is usually administered in agricultural settings, some homeowners use it to eliminate yellow foxtail and intrusive vines, such as morning glory.
This is used to stunt the growth of vining plants and invasive grasses.

In addition to the type of weeds you experience, it’s also important to consider the size of your lawn and the amount of effort you’re willing to put into treatment. For example, if you have a small area that you need to treat quickly, a granular pre-emergent may be a good option. However, if you’re looking for an even application across a large area and don’t mind a little pre-application mixing, a liquid pre-emergent could be a good choice.

Important Tips for Using Pre-Emergent Herbicide

Before applying pre-emergent weed control, consider the following application tips:
Apply pre-emergent evenly—To completely protect your lawn from weeds, you’ll need to ensure no corner of your lawn is untouched.
Don’t forget water—Herbicide applications are activated by water, which distribute chemicals throughout your lawn’s soil. To save water, you can apply pre-emergent before an expected rainfall. However, if rain isn’t in the forecast, be sure to water your lawn after application.
Limit lawn activity—It’s important to ensure that the soil holding the pre-emergent is undisturbed after application. As such, you shouldn’t aerate after application and you should hold off on mowing until after the pre-emergent has been watered.
Maintain your lawn—Maintaining a healthy lawn can help it naturally compete with common weeds. Routine maintenance should include mowing, proper irrigation, and controlling pests. If you don’t have time to maintain your lawn, consider hiring a lawn care service, such as TruGreen or Lawnbright.

Frequently Asked Questions

Is a pre-emergent a herbicide?

Yes. Herbicides are chemicals that kill weeds and other unwanted plants to protect surrounding vegetation. Unlike many herbicides, pre-emergents stunt the growth of weeds before they sprout.

What happens if I apply a pre-emergent too late?

If you apply a pre-emergent after the weeds have already germinated, it will be ineffective in preventing weed growth during the spring or summer. Pre-emergent will only work when applied before grass weeds crop up.

Can I apply a pre-emergent in my flower bed?

Yes. Pre-emergents can be applied on lawns and flower beds to prevent weed seeds from growing and damaging healthy grasses, flowers, and vegetable gardens. Apply pre-emergents after any flowers or plants have started to grow to prevent the chemicals from killing ungerminated seeds.

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