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Rochel Maday is a contributing writer for Å˽ðÁ«´«Ã½Ó³» Homefront. She specializes in home improvement topics and is dedicated to providing valuable information that empowers homeowners to tackle their projects with confidence. Her work has been published in Angi, Bob Vila, Forbes and elsewhere. When not writing, Rochel enjoys digging into gardening projects and watching documentaries with her husband and their four kids.
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Preemergent herbicide is a weed killer applied to soil before weeds germinate.
Measuring soil temperatures is the best way to determine when to apply preemergent.
Several varieties of preemergent herbicides exist, including liquid, granular, selective and nonselective.
Keeping your lawn’s grass green and healthy doesn’t come easy, but preemergent herbicides can help.
A preemergent herbicide is a weed killer applied to soil before weed seeds germinate, preventing them from sprouting and establishing roots. Knowing when to apply preemergent is crucial for success. Spraying too early or late in the growing season can result in wasted resources and triumphant weeds.
The best time to apply preemergent herbicide is typically in early spring before soil temperatures consistently reach 55 degrees Fahrenheit. But with so many types of weeds and climate variations, there’s no one-size-fits-all approach to applying preemergent.
We reached out to Craig Elworthy, founder of DIY natural lawn care company , to learn about all things preemergent. Below, we explain the several types of preemergent and how to apply them for a greener lawn this year.
In many U.S. regions, you should apply preemergent herbicide in March or early April, just as the grass begins to sprout. While no one month applies to all areas because of varying climates and conditions, you can use the following as a general guideline:
According to the , 80% of crabgrass germination occurs when soil temperatures are consistently between 60 and 70 degrees Fahrenheit. Getting a preemergent treatment beforehand — when the soil temperature measures between 50 and 55 degrees Fahrenheit — allows enough time for the application to be effective.
There are several ways to check soil temperature. One simple method is to insert a soil thermometer into the top inch of the soil (this is where most weed seeds germinate, so don’t go much deeper) and leave it for a few minutes to get an accurate reading. A kitchen meat thermometer can work in a pinch if you don’t have a soil thermometer.
Another simple way to determine soil temperature is to refer to a weather website or gardening app that provides for specific locations.
Since preemergent prevents seeds from germinating, applying it too early can stop the germination of desirable plants, such as grass or flowers.
An early application can also be ineffective since preemergent creates a temporary barrier lasting only a few months. “If you are too early with your application, it can wear off before weeds actually get going,†said Elworthy.
It’s best to time your preemergent with soil temperature. This way, you allow your grass and flowers to take root yet catch weeds just as they’re beginning to develop.
Your preemergent application process will depend on the type you choose — liquid or granular. If you’re not sure which is best, here are a few considerations to keep in mind.
Granular herbicides:
Liquid herbicides:
Once you determine which type to use, you can plan out your approach. Here are simple guidelines for both varieties.
First, gather your supplies:
Mix your liquid preemergent with water according to the label and add it to your sprayer. Using the same technique you use to mow your lawn, apply your preemergent to the target area in a row-by-row pattern. Make sure to turn your irrigation system off for the recommended amount of time — typically at least 12 hours.
You’ll need a few supplies:
Prepping granules starts with reading the label carefully, including its safety tips, application rates and precautions. Once you have the application rate, fill your spreader and adjust the settings accordingly, keeping the size of the treatment area in mind for uniform coverage. Before you begin, choose a crank speed that covers the appropriate distance.
When applying a granular preemergent, walking in opposite directions on both sides of the area you’re targeting is best. Pass over the same area a few times to prevent an uneven application. Do your best to keep a steady pace. Once you’re done, follow the product’s watering instructions to activate the herbicide.
Preemergent herbicides typically need to be watered in after application to activate correctly. However, the time window you’re working with depends on the type of herbicide, which is why reading the product label is so important.
For liquid preemergent, you’ll likely need to wait several hours for the solution to become rainproof. Otherwise, a sudden shower could dilute the product before it has time to get into a plant’s vascular system.
On the other hand, granular preemergent herbicides typically come with specific instructions regarding how much water they require for activation and a suggested timeline.
“Liquids get into the soil immediately. Granular takes longer to break down and get into the root zone,†said Elworthy. “It needs to be watered in immediately, or it will gas off into the environment,†he continued.
When using granular preemergent, Elworthy suggested timing your application just before a rainstorm or making sure your irrigation is turned on.
Mowing is not a factor in a preemergent application because the grass isn’t typically growing when you apply it. Soil temperatures must be between 50 and 65 degrees Fahrenheit for cool-season grasses (and, as the name would suggest, even warmer for warm-season grasses) to germinate.
If you’re applying preemergent within the appropriate time window in early spring, you’re unlikely to have grass tall enough to mow just yet.
However, as the growing season goes on, you may find it easier to achieve an even application if you mow beforehand when applying additional herbicide, such as a fall preemergent.
It’s also important to note that should you apply an herbicide later in the season (after weeds have sprouted), you don’t want to mow directly after an application. It takes at least 24 hours for broadleaf weeds to absorb herbicide, so if you cut the lawn too soon after applying it, you’re not letting it get into the plant.
A preemergent can last anywhere between one and eight months. Professional products last six to eight months, while DIY products usually last between three and four months with the proper application rate.
While everyone’s needs are different, most lawns can benefit from two to three preemergent applications a year.
Weeds respond differently to different preemergents. Choosing the right product for your yard starts with understanding what each variety is designed to accomplish.
You should ask yourself four questions when choosing a preemergent for your lawn:
Preemergents are generally considered safe for people and pets. However, there are a few risks to be aware of:
Preemergent herbicide is only one piece of the lawn care puzzle. You can take several other actions to complement preemergent herbicides, including regular mowing, proper watering and overseeding.
Keeping your lawn at the appropriate height helps shade the soil and discourages weed seeds from germinating. Deep and infrequent lawn watering encourages deep root growth in your grass while filling in bare patches by overseeding with grass seed promotes a dense lawn resistant to weed invasions.
Combining preemergent herbicides with proper lawn maintenance techniques lets you keep weeds at bay and maintain a beautiful and healthy lawn year-round.
Editorial note: The name “Homefront” refers to the alliance between Å˽ðÁ«´«Ã½Ó³» and Home Solutions that publishes review, comparison, and informational articles designed to help Å˽ðÁ«´«Ã½Ó³» readers make smarter purchasing and investment decisions about their home. Under the alliance, Homefront provides and publishes research and articles about home service and home improvement topics.
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