Pre-emergent weed control is essential for keeping crabgrass and other weeds out of your lawn, but knowing when and how to apply it are critical for success. In this article, we will walk you through how we use pre-emergent to protect our customers’ lawns from crabgrass all season long. This article covers what pre-emergent is, how it works, when to apply it, and tips for getting the most out of your application.
What is Pre-Emergent and why it is Essential?
A lush, green lawn is every homeowner’s dream, but pesky weeds can quickly ruin that vision. A key step to keeping a weed-free lawn is proactive weed control, and that’s where pre-emergent herbicides come in. A pre-emergent herbicide treatment (or just “pre-emergent” for short) is applied early in the lawn care season and creates a barrier in your soil, blocking many types of weeds. Pre-emergent is great because, when applied correctly, it stops many weeds from appearing in your lawn in the first place. Additionally, the benefits of pre-emergent last for months, protecting your lawn all season. In comparison, weed killers (also called “post-emergent herbicides”) only work on weeds that are already there, and they don’t last long, so you might have to spray multiple times to keep your lawn weed-free.
More than just crabgrass prevention
Pre-emergent herbicides are best known for stopping crabgrass, but they also help prevent many other common annual weeds. These include foxtail, goosegrass, barnyardgrass, spurge, knotweed, purslane, and more. In the Iowa City area, we often see Japanese stiltgrass in shady, untreated lawns. By applying pre-emergent at the right time, you can block a wide range of weeds before they ever appear. This saves you time, effort, and frustration later in the season.
When Should You Apply Pre-Emergent?
Timing is critical when it comes to applying pre-emergent herbicides. Apply pre-emergent in early spring, typically when soil temperatures reach 50°F. This is when many common weeds, like crabgrass, begin to germinate. In Iowa, this usually falls between late March and mid-April. A very helpful tool for timing your application is the Michigan State University Growing Degree Day (GDD) Tracker, which estimates soil temperatures and helps predict when crabgrass is likely to germinate based on your location.
Some lawn care advice includes applying pre-emergent in the fall, but that’s generally just for southern states where warm-season grasses and mild winters allow weeds to grow year-round. In Iowa and the Midwest, cool-season grasses go dormant in winter and the most problematic weeds like crabgrass don’t start growing until the spring. For most lawns here in Iowa, a spring pre-emergent application is all you need.
Tips for Applying Pre-Emergent
- Read the Label: Each pre-emergent product is different, so always follow the manufacturer’s instructions for application rates and timing to ensure effective weed prevention.
- Water It In: After applying pre-emergent, you need to lightly water your lawn to help move the product into the soil and activate it. Once it’s watered in, it binds to the top layer of soil and forms a barrier that keeps working for months. Rain can take care of this step naturally, but make sure it’s no more than a modest rain. A heavy downpour could wash the product away before it has a chance to bind to the soil.
- Avoid Disturbing the Soil: Raking or aerating your lawn after applying pre-emergent can break the chemical barrier, reducing its effectiveness.
Limitations and precautions
While pre-emergents are a powerful tool, there are a few important limitations and precautions to keep in mind:
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Do not apply pre-emergent if you plan to seed in the spring. Pre-emergents block seed germination, so they will prevent your new grass seed from growing.
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Too much pre-emergent can harm your lawn and the environment. Overapplication can stress your grass and may interfere with fall overseeding. Stick to the label rates to stay safe and effective.
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Too little product won’t protect your lawn for long. A weak application may wear off mid-season, leading to a flush of weeds later in the summer.
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Uneven coverage leads to patchy results. If you miss spots or don’t apply evenly, you may still see weeds pop up in untreated areas.
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Pre-emergent does not kill existing weeds. It only stops certain weeds before they sprout and won’t affect anything already growing.
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Wear the recommended safety gear. Always follow the product label and wear gloves, eye protection, and other personal protective equipment (PPE) as directed during handling and application.
Ready to Take Control of Your Lawn?
Adding pre-emergent herbicides to your lawn care routine will save you time and effort in the long run. By addressing weeds before they sprout, you’ll enjoy a healthier, more attractive lawn with fewer weeds to pull or treat later in the season. Plus, maintaining a weed-free lawn will enhance your property’s curb appeal and overall value.
At Heartland Grounds, we’re passionate about helping you achieve a lawn that looks great and stays weed-free all season. If reading this article made you realize how much planning and effort goes into proper lawn care, don’t worry. We’re here to take that burden off your shoulders. Our team is trained, licensed, and experienced in applying lawn treatments at just the right time for Iowa lawns. Whether you want to prevent crabgrass, clean up existing weeds, or just enjoy a healthy, green yard without the hassle, we’ve got you covered.
Visit our weed control page to learn more about how we can help or get in touch today for a free estimate. Let Heartland Grounds handle the hard work so you can spend more time enjoying your lawn.
Written by Stephen Presti, Licensed Lawn Care Applicator and Owner of Heartland Grounds
Last edited: August 4, 2025