If you’re aiming for a weed-free lawn this year, understanding pre-emergent herbicides is key. Pre-emergent herbicide is a type of weed killer that works by preventing seed germination. That means you have to apply it before grassy weeds like annual bluegrass and poa annua (meadowgrass) even have a chance to sprout. The timing of the application is crucial. For warm-season grasses like Bermuda and St. Augustine, applying in early fall can make a huge difference.
Whether you’re seeding a new lawn or maintaining established grass, pre-emergents help keep your lawn looking its best. For tall fescue or any other grass type, pairing pre-emergent herbicides with lawn food or lawn fertilizer helps your yard remain lush and healthy year-round.
In this article, I’ll explain all you need to know about pre-emergent herbicides to make your gardening life easier.
How Does Pre-Emergent Herbicide Work?
Pre-emergent herbicides work by forming a protective barrier in the top layer of your soil, stopping seeds from sprouting into full-blown weeds. Once you apply the herbicide, it lingers in the soil, ready to coat any seeds that come into contact with it. This prevents the seeds from developing roots and shoots, effectively stopping them in their tracks. It’s like putting up an invisible fence or barricade that weeds can’t cross.
While pre-emergents can tackle a variety of lawn weeds, they’re particularly effective against crabgrass, which can quickly take over if left unchecked. The secret sauce in these herbicides includes active ingredients like dithiopyr, isoxaben, and prodiamine. Each of these chemicals targets different types of weeds, giving your lawn a broad-spectrum defense. I recommend keeping pre-emergent herbicides in your lawn care arsenal. By applying a pre-emergent at the right time — usually in early spring or early fall — you can keep your lawn looking lush and weed-free.
If you’re having a hard time controlling crabgrass, there are ways to effectively eliminate it beyond applying pre-emergent herbicides.
When To Apply a Pre-Emergent Herbicide
To get the best results with pre-emergent herbicides, apply them before weeds start to germinate. For general treatment, aim to apply your herbicide in early spring, just before those pesky annual weeds typically appear. Proper timing is essential, as pre-emergent herbicides work by creating a barrier in the soil that stops weed seeds from taking root.
If you’re unsure when weeds typically appear in your area, a good rule of thumb is to apply your herbicide when the weather consistently hits between 65 and 70 degrees Fahrenheit for at least four days. If you’re still unsure, don’t hesitate to ask for advice from a local gardening center or university cooperative extension.
For optimal control, consider a second application about 6 to 8 weeks after the first one. This can help reinforce your weed defense and keep your lawn looking great. Always check the label on your herbicide for specific timing recommendations, as different products may have varying instructions. By staying on top of your application schedule, you’ll keep your lawn weed-free and thriving throughout the season.
Fall Pre-Emergent Application
While it’s not necessary, you can apply a pre-emergent herbicide twice a year — in spring and fall — to help prevent a garden full of weeds. I apply it to my lawn, and it seems to work well in keeping weeds at bay. Wait until the temperature drops below 70 degrees Fahrenheit before applying, which usually happens in September or October.
Remember, don’t wait too long to apply. An herbicide won’t work if weeds appear before you apply it. Likewise, don’t apply it too early, as rain can wash it away or cause it to travel too deep into the soil. If you’re unsure when to apply your herbicide, it’s better to apply it too early than too late.
How To Shop for Herbicides
To choose which herbicide weed preventer to buy for your summer and winter annual weeds, you’ll want to take note of what type of existing weeds tend to grow on your lawn. The same variety of weeds typically pop up year after year. Noting the types of weeds that sprout on your lawn can help you figure out which type of pre-emergent herbicide to buy the following season. Your local garden store can help you determine which herbicide will target your weeds.
Keep in mind that no pre-emergent herbicide can target all varieties of weeds. Some pre-emergent herbicides kill a broad range of common lawn weeds, while others target specific weeds like crabgrass or chickweed.
To target the spectrum of weeds present on your lawn, I recommend using two types of herbicides. One type is for controlling turfgrass weeds, and the other should control broadleaf weeds.
You’ll also need to decide whether you want to use a liquid or granular pre-emergent herbicide. Plan to mix liquid herbicides with water if you buy them in a concentrated form and apply them with a sprayer. (You can either buy or rent a sprayer.) With granular varieties, you can apply by hand or with a spreader or shaker bag.
Water your lawn within a few days of application for the herbicide to be effective, as the water allows the herbicide to spread deeper into the soil. Most pre-emergent herbicides are chemical-based, but there are a few natural and organic varieties available. Before applying, know that diluting the herbicide more than the recommended amount can greatly reduce its efficacy. For this reason, it’s important to apply the herbicide according to its directions.
If you’d like to explore natural and organic herbicide options, I recommend you read our article on how to make organic herbicides.
Pre-Emergent Herbicide Buyers Guide
With so many pre-emergent herbicides on the market, choosing the right one for your lawn can be challenging. When you select a pre-emergent herbicide, consider several factors to find the best product for your needs.
Price
The cost of a pre-emergent herbicide can be a huge deciding factor when choosing the right product. While a $100 bottle of herbicide seems like a big expense at first, it will last longer and cover more area than a small $25 bag. Paying more for the product in bulk can save you money in the long run.
Region
Depending on where you live, you might need to look into different options. If you live in an area that gets a lot of rain, a liquid pre-emergent will work faster and stay in the soil longer. There are some granule pre-emergents that work well with rain or snowfall, so it is best to look into the specifics before purchasing a product.
Equipment
If you use a liquid pre-emergent herbicide, you’ll need to also purchase a pump sprayer for your herbicide applications so you can evenly coat your lawn. According to our research, a good pump sprayer can cost up to $100, so you should keep the price of additional equipment in mind before purchasing a product.
Once you apply the herbicide, leave the soil alone. Disturbing soil by aerating your lawn or cultivating it in any way can disrupt the top layer of soil where the herbicide has created a barrier. After applying pre-emergent herbicide, avoid digging or doing anything else to disturb the top layer of soil.
Not Interested in DIY Landscaping?
As a homeowner, you might just not have the time or interest in handling your own lawn care and weed control. Between work, family, and everything else on your plate, spending your weekends dealing with weeds and fertilizers might feel like a lot. If that sounds familiar, you’re not alone. Many people find it easier to let professionals handle the lawn care.
The best lawn care services, like TruGreen, offer additional services like fertilization, weed control, aeration, seeding, and more. TruGreen is a top-recommended provider for all of your lawn care needs. And learn more with our TruGreen Review.
Compare these top lawn weed control services:
Final Thoughts on Pre-Emergent Herbicides
Weeds can quickly turn a pristine lawn into a tangled mess, making it tough to grow the plants you actually want. Pre-emergent herbicides offer an affordable and effective solution to keep these unwelcome invaders at bay before they even get a chance to sprout. By applying these herbicides at the right time, you can maintain a lush, healthy lawn and prevent weeds from taking over.
However, not everyone wants to dive into DIY lawn care. If managing weeds and applying treatments feels overwhelming or just isn’t your thing, you have plenty of options. Whether you decide to tackle the problem yourself or bring in a professional, you can find a solution that fits your needs and keeps your yard in top shape.
Frequently Asked Questions
Is pre-emergent a weed killer?
Pre-emergent doesn’t kill weeds that have already come out of the ground. Instead, it prevents weed seeds from germinating, stopping any new weed growth.
Is pre-emergent worth it?
Pre-emergent is effective in preventing certain weeds from overtaking your lawn. If you apply it properly, it’s definitely worth it, since it prevents weeds from spreading. It prevents crabgrass and also works well in preventing dandelions, fescue, spurge, bluegrass, foxtail, and nutsedge from spreading.
What is the difference between pre-emergent and post-emergent?
Pre-emergent herbicide prevents weeds from growing within the soil. Post-emergent herbicide kills weeds after they’ve already come out of the ground.
