Weed Control: Pre-Emergent vs Post-Emergent Herbicide Explained

If you’re like a lot of homeowners, weeds are the bane of your existence. But when it comes to the most effective weed control, you want to make sure that you’re taking a varied approach using different products.

Different weeds are going to be a problem at different times of the year and for that reason, a varied weed control approach is going to get you the most success.

This includes the use of both pre-emergent and post-emergent herbicides.

In this article, we’ll explain the difference between pre-emergent and post-emergent herbicides and why both need to be part of your weed control plan.

The biggest difference between pre-emergent and post-emergent herbicides is when they work. Pre-emergent products help stop certain weeds before they have a chance to grow, while post-emergent products target weeds that have already popped up in your lawn.

In most cases, an effective weed control program will use both.. While pre-emergent weed control can help prevent a lot of weeds, no product is going to stop every single one. Post-emergent treatments help take care of the weeds that still manage to break through.

What Is Pre-Emergent Herbicide and How Does It Work?

Pre-emergent weed control works by helping to prevent certain weeds from becoming established in the first place. These products create a barrier in the soil that interferes with weeds as they begin to germinate.

It’s a proactive approach that plays a really important role in preventing annual grassy weeds like crabgrass. However, pre-emergent products do not work on every variety of weed, and they won’t get rid of weeds that are already growing. That’s why other weed control products are also important.

There is a limited window of time in which pre-emergent products will work. They must be applied before the targeted weeds germinate in order to be effective.

Here in New England, crabgrass typically begins germinating once soil temperatures remain around 55 degrees for several days. But the exact timing can change slightly from year to year depending on the weather. By the time you can actually see crabgrass growing in your lawn, it’s usually too late for pre-emergent control to stop it.

What Is Post-Emergent Herbicide and How Does It Work?

While pre-emergent products can help prevent a lot of crabgrass and other targeted weeds, there is almost always going to be some breakthrough. This is why post-emergent products are also an important part of a complete weed control program.

As the name implies, post-emergent herbicides work on weeds that have already germinated and are actively growing in your lawn.

Depending on the product being used, post-emergent treatments can help control common weeds like dandelions, clover, plantain, chickweed, and certain grassy weeds. But there is no single product that works on every weed. Properly identifying the weed is important so that the right control can be applied at the right time.

Post-emergent products also tend to work best when weeds are actively growing. Weather conditions, the size and maturity of the weed, and the type of product being used can all impact how well a treatment works.

Do You Need Both Pre-Emergent and Post-Emergent Weed Control?

For most lawns, the answer is yes.

Pre-emergent and post-emergent products perform two different jobs. Pre-emergent treatments help reduce the number of targeted weeds that appear, while post-emergent treatments address weeds that are already growing or that manage to break through.

Using only post-emergent products means that you’re always reacting to weeds after they become a problem. But relying only on pre-emergent weed control can leave you without a solution for weeds that are already established or aren’t controlled by the pre-emergent product.

A comprehensive weed control program takes both approaches. It also adjusts treatments throughout the growing season based on the types of weeds that are present and the condition of your lawn.

There’s More to Weed Control Than Pre-Emergent and Post-Emergent Herbicides

There’s no doubt that pre-emergent and post-emergent herbicides are an important part of your weed control program. But there’s more to it than that. 

There are also specialty controls that are sometimes required…and there’s the need for an overall lawn care program that focuses on promoting a thick and healthy lawn.

The truth is, when your lawn grows thick and healthy, it will start to naturally choke out weeds on its own. That’s truly the best approach to weed control that you could ever take. Over time, you’ll need fewer control products as your lawn will begin to crowd out those unwanted invaders.

Ultimately, you want to choose a lawn service that takes a comprehensive approach to weed control. Our crabgrass and weed control services combine preventive treatments, targeted weed control, and an overall lawn care program designed to promote thicker, healthier turf.

Frequently Asked Questions About Pre-Emergent and Post-Emergent Herbicides

Does Pre-Emergent Kill Existing Weeds?

No. Pre-emergent products are meant to help prevent certain weeds before they become established. If a weed is already visible and actively growing, it will typically require an appropriate post-emergent treatment.

This is one reason why timing is so important. Once weeds like crabgrass have already emerged, that window for preventing them with a pre-emergent treatment has passed.

Can You Apply Pre-Emergent and Post-Emergent Herbicides at the Same Time?

In some cases, pre-emergent and post-emergent products may be used during the same general treatment period. But they are still doing two different jobs.

The right approach will depend on the weeds that are present, the time of year, weather conditions, and the products being used. It’s not about applying as many products as possible. It’s about using the right products at the right time.

Why Do Weeds Still Appear After Pre-Emergent Is Applied?

Unfortunately, no pre-emergent application is going to prevent every single weed.

The timing of the application, weather conditions, soil disturbance, product coverage, and the variety of weed can all play a role in breakthrough. Some weeds also aren’t controlled by traditional pre-emergent products.

That doesn’t necessarily mean the treatment failed. It’s why ongoing monitoring and targeted post-emergent treatments are still an important part of a complete weed control plan.

Let Go of Your Weedy Worries

There’s no doubt that weeds can be a major nuisance. But when you invest in professional lawn care services in Southern NH, ME, and MA, you can enjoy more time outside without being burdened or stressed by weeds. 

At Seacoast Turf Care, we take weeds seriously. We provide lawn care services in Southern NH, Southern Maine, and Northeastern Massachusetts and our emphasis is on a science-based approach that promotes a healthier lawn. When you partner with us, you can finally let go of your weedy worries. 

Ready to be where the grass is greener, healthier, and free from weeds? Get lawn care pricing for your Southern NH, ME, or MA lawn.