Fighting lawn weeds in spring will reduce chores through the summer and into fall. Learn about chemical and organic weed-control methods. Weeds and other undesirable intruders fall into three categories: annuals, perennials, and coarse weed grasses. Pre-emergent herbicide is a crucial step in eradicating weeds. Learn about pre-emergents, when to apply, how to apply, and how to choose the right one for you.
Spring Control of Lawn Weeds
Kelly Burke is a professional turf manager for a manicured corporate campus in New England. He is accredited in organic land care and is a licensed pesticide applicator. He formerly managed the turfgrass as a golf course superintendent and has held several senior management positions at private country clubs overseeing high maintenance lawns.
Amanda Rose Newton holds degrees in Horticulture, Biochemistry, Entomology, and soon a PhD in STEM Education. She is a board-certified entomologist and volunteers for USAIDs Farmer to Farmer program. Currently, she is a professor of Horticulture, an Education Specialist, and pest specialist.
twomeows / Getty Images
Controlling lawn weeds is an ongoing battle, especially if you are the type of homeowner who insists upon a lush, deep-green lawn devoid of anything but the recognized turf-grass species. And this is not a battle you win with a single-time effort. Wind, birds, your lawnmower, and even your feet are constantly delivering new weed seeds to your lawn. Many of these seeds will dwell in the soil for as much as 50 years, awaiting the right moment to germinate, sprout, and torment you with their presence.
Don’t give up, however. While achieving and keeping that dream lawn does require some year-round attention, a diligent approach in spring means you’ll spend more time enjoying your lawn and less time maintaining it through the summer and into fall.
Types of Weed Killers
The chemical weedkillers (herbicides) most commonly used on lawns can be formulated to kill broadleaf weeds like dandelions and chickweed, or they can be designed to kill other competing grass-like weeds, such as crabgrass, quackgrass, and nutgrass. There are also combination products, containing the chemicals to kill both broadleaf weeds as well as grassy weeds.
Beyond this, chemical herbicides come in two general categories: pre-emergent and post-emergent. A pre-emergent herbicide is a weed killer applied prior to the germination of the weed seed and the subsequent emergence of the weed seedling from the soil. Pre-emergent herbicides are sometimes applied in the late fall in warm-weather regions, but in cold-weather regions, they are usually applied in the early spring before the turf grasses have begun to actively grow. One advantage of pre-emergent weed killers is that they can prevent mid and late-summer weeds, such as plantains, before they even appear.
In the pre-emergent class, chemicals like dithiopyr (Dimension) and pendimethalin (Lesco’s Pre-M, Scotts’ Halts) prevent all seeds from germinating, including grass seed. You should be aware that grass seed cannot be applied for 6 to 12 weeks after application, depending on the specific product. Another chemical, siduron (Tupersan) prevents only weed seeds from starting, allowing grass seeds to germinate. However, it is costlier and best used sparingly.
Post-emergence herbicides are a different class entirely. They are applied as weeds begin to appear in the lawn, as they must come into contact with actively growing leaves in order to do their work. These herbicides are generally applied at various intervals in late spring through summer, as weeds enter their periods of most intense growth.
Most post-emergent chemicals are considered selective herbicides, in that they are formulated to kill only certain classes of lawn plants while leaving desirable turf grasses untouched. There is another class of herbicides known as non-selective, which will kill any growing plant. The best-known of these is Round-Up, but there are other similar products, Nearly all of them contain a chemical known as glyphosate, well-known as a general plant killer. Glyphosate-based herbicides are sometimes carefully applied to spot-treat individual weeds that resist other methods, but the only time you would consider using major applications on a lawn is if you want to kill it off entirely prior to creating a new lawn through seeding or sodding. Plenty of people have ruined lawns by broadly applying glyphosate by mistake.
Glyphosate is a controversial chemical. It was initially touted as a plant killer that was quickly rendered inactive upon contact with common soil microbes, and was thus preferred to chemicals that persisted in the soil and could run off and enter groundwater supplies. This advantage is quite real. However, glyphosate is now thought to also pose health risks, especially for farmers and other workers who handle the chemical frequently and in large concentrations. The dangers are probably low for homeowners who use it occasionally as a landscape herbicide for spot application and who follow label directions exactly, but it is important to avoid skin contact or breathing the spray mist.
It’s critical to choose the right chemical weed killer to address the specific weeds that are appearing in your lawn.
Many people are reluctant to use synthetic chemicals of any kind on a lawn for environmental reasons. For these homeowners, there are a variety of organic herbicides that can be tried, ranging from ordinary household vinegar to commercial preparations that usually contain a combination of vinegar, salts, and soaps.
Spot Treatment Is Better Than Broadcast Application
It’s no surprise that manufacturers of lawn care products, many of which publish a lot of online advice articles, insist that applying lots of chemicals over the entire lawn is the best way to control weeds. Their advice begins with broadcast application of pre-emergent herbicides in the fall or early spring, and continues with at least one, and preferably multiple, widespread applications of post-emergent herbicides at different intervals through the spring.
The advice becomes much different when you consult academic sources, such as the lawn-science departments at various universities. These scientific experts understand the dangers that over-application of herbicides, pesticides, and chemical fertilizers pose to water sources through run-off, and here the advice is always to treat weeds in the least toxic method possible, avoiding broad applications of chemicals whenever possible.
Instead, they argue it is best to avoid chemical means if possible, and if they are unavoidable, to spot-treat individual weeds with a spot-targeted spray rather than to spray or spread a dense layer of chemical over the entire lawn. Spot-treating weeds may sound like a lot of work, but a homeowner soon finds that it’s not a great burden to follow weekly lawn-mowing chores by walking the lawn with a hand sprayer and applying a small dab of weed killer to the weeds that are spotted. Over time, as most of the weeds are killed, it becomes relatively quick work .
Avoid Weed-and-Feed Products
One practice that nearly all academic lawn-science experts frown upon is the use of combination weed-and-feed products that combine both pre-emergent or post-emergent herbicides and fertilizer products in one granular or spray-on product. These products were developed and marketed by lawn chemical companies with the promise of saving time by applying the fertilizer and herbicide all at the same time.
The problem is that the optimal time for feeding a lawn is much different than the optimal time for applying weed killers. If you time the application for the optimal feeding time, then it’s too late for the herbicides to work effectively, and the chemicals generally run off into water supplies. In fact, some countries, such as Canada, have banned the use of combination weed-and-feed products entirely.
To this day, lawn chemical companies fiercely argue that these products are safe and effective, while university-based lawn-science expert argue with equal ferocity that they should be avoided or even outlawed. Generally speaking, it is a better practice to apply fertilizers and weed killers separately, at the times most appropriate for their effectiveness.
Homeowners devoted to environmentally sound gardening practices are always on the lookout for organic, non-chemical means of dealing with lawn weeds. For pre-emergent lawn weed control, the only truly organic strategy is to use corn gluten meal.
Corn gluten is a well-known feed meal commonly used on hog farms, but it was also discovered to have pre-emergent characteristics for preventing crabgrass and other lawn weeds. However, for corn gluten to be effective, the application has to be very carefully timed, laid down just before the weed seeds germinate. And because weeds germinate at different times, corn gluten may require multiple applications. Applied just a few days too late, and the corn gluten becomes a fertilizer that causes weeds to grow even more vigorously. Thus, the early promise of corn gluten has now been tempered by the reality—it is hard to use effectively.
There are a variety of post-emergent home remedies for controlling weeds, including spraying them with a solution containing household vinegar or dish soap. There are also commercial preparations that contain no synthetic chemicals. These usually are some combination of vinegar, soaps, and salts. You can also use a flame torch to kill weeds with pure heat.
The most environmentally friendly method of all is to kill or remove the weeds by hand. This is most practical for small lawns, but it is feasible even for large lawns. Gardeners who stay on top of the duties beginning in early spring soon find that a lawn can become quite clean as the seed-producing weeds are gradually eradicated. There are a variety of helpful tools for removing lawn weeds by hand. One of the most useful is the “weed popper,” which allows you to pull up a weed, roots and all, from a standing position.
Spending an hour or so once a week pulling weeds by hand after mowing is completed can keep a lawn largely free of most weeds.
Common Lawn Weeds That Appear in Spring
There are a variety of common lawn weeds to deal with, which can be categorized according to leaf shape—broadleaf weeds vs. grassy weeds. Or, they can be categorized by their seasonal growth habit—annual weeds vs. perennial weeds.
The types of weeds you fight will vary depending on the region where you live—some are more problematic in warm growing zones, while others are unknown except in colder regions with freezing winters. Here are some of the more common weeds you may encounter beginning in spring:
Crabgrass (Digitaria spp): Crabgrass gets its name from the leaves, which form a tight, crab-like circle. This annual weed tends to appear in weak or bare areas of a lawn. Both over- and under-watering favor its growth, as does consistently mowing the lawn too short. Crabgrass can be treated with pre-emergence herbicides in the spring, which will keep the seeds from sprouting, or they can be treated with post-emergent herbicides as the weeds are noticed, beginning in spring. Check with your local extension office or a reputable garden center to fine-tune timing in your region. Crabgrass clumps can also be removed by hand, which is best done when the lawn is quite moist.
Quackgrass (Elymus repens): At first glance, quackgrass looks a lot like crabgrass, but it is typically a cool-season grass that spreads by rhizomes without the shallow clumping habit of crabgrass. This is a perennial weed that can be very hard to eradicate. While there are both pre-emergent and post-emergent herbicides that will stunt quackgrass, the best solution is often to very carefully apply a broad-spectrum, glyphosate-based herbicide that kills the weed, roots and all. This is a very hard weed to remove by hand, since the roots are very tenacious and far-reaching.
Dandelion (Taraxacum spp.): One homeowner’s lawn weed is another’s wildflower, and nowhere is this more true than with the colorful dandelion, an icon of late spring. Many a homeowner fumes over neighbors who allow this prolific annual plant to thrive, as a single flower head allowed to go to seed can blow many thousands of seeds around the neighborhood. This common weed/wildflower can be prevented by some pre-emergent herbicides, though the application needs to be quite thick. More appropriately, it can be spot treated with a post-emergent herbicide or very careful spot application of a broad-spectrum glyphosate-based plant killer. Try to kill this weed before it flowers and sets seeds.
Creeping Charlie (Glechoma hederacea): Sometimes known as “ground ivy,” creeping Charlie is a perennial creeping plant with tiny heart-shaped leaves and indigo-colored flowers. While there are those homeowners who like its appearance and allow it to roam freely as a ground cover for shady areas, most people rue the day that it arrives in the yard. Charlie spreads quickly both through self-seeding and creeping stolons. Although the roots are fairly shallow, this is a very hard plant to remove by hand. A selective broadleaf herbicide, preferably applied as a spray spot treatment, is an effective approach, although you may find it takes multiple applications. With lawns extremely infested, some homeowners opt to kill off the entire lawn with a non-selective glyphosate-based herbicide, then start over from scratch by seeding or sodding a new lawn. While organic gardeners are constantly looking for low-impact, natural ways to combat Charlie, most of the methods used—such as applying Borax or baking soda—have not shown much long-term effectiveness.
Wild Violets (Viola spp.) : This is another plant that more organically-minded gardeners may view as a wildflower, choosing to encourage rather than fight it. And it’s true the heart-shaped leaves and purple or white flowers can be quite attractive as a ground-cover. For areas where traditional turf grass won’t thrive, a ground cover dominated by wild violets is not a bad choice. But if you do decide to combat wild violets, they are best approached with a spot treatment of broadleaf herbicide. Fall is the best time for major treatment, but violets that pop up in the spring should be treated as you spot them. These clump-forming weeds are also easy to remove by hand if the ground is nice and moist. Some people have good luck coating the leaves with ordinary dish soap, which starves the plant of oxygen.
Chickweed (stellaria media): This is a very pesky annual plant that appears all across the U.S. as low-growing vine-like stems with small egg-shaped leaves and tiny white flowers. While major infestations are best treated with a pre-emergent herbicide applied in fall, plants that appear in spring can be spot-treated with a post-emergent broadleaf herbicide. Chickweed is also fairly readily killed by spraying with ordinary household white vinegar. Keep your lawn mowed short to prevent the plant from flowering and setting seeds.
Purslane (Portulaca oleracea): This annual weed grows in low mats with reddish stems and oval-shaped succulent leaves. It becomes a more severe problem in the humid, hot days of later summer, but you may see early plants appear in spring. It is a fairly easy plant to prevent by application of a granular pre-emergent herbicide, and it is readily killed by spot treating with a post-emergent broadleaf herbicide. And it is quite easy to break off the plant at ground level, which will prevent it from flowering and setting seeds. This may be the best choice of all, as purslane is an exceedingly healthful plant that rivals spinach for sheer nutritional value. It can be eaten raw in salads or sauteed as a side dish. Naturally, it should not be harvested for eating if you have applied any herbicide in the area.
Clover: The reputation of white clover (Trifolium repens) has undergone many iterations over the years. Years ago, it was deliberately included in lawn grass seed mixes, but as expansive suburban lawns of pure green became the vogue, clover began to be considered a lawn weed, with great efforts made to eradicate it from lawns. Today, it is coming back in style for a variety of reasons. Clovers are good low-moisture ground-covers that are also much favored by pollinator bees who feed on the flower pollen. Clover lawns require less mowing, and the plants fix nitrogen in the soil, meaning that the lawn will require less fertilization. It is not at all uncommon today to find homeowners introducing clover into their lawns through regular over-seeding. Before you make efforts to eradicate it, consult a local university extension service for their advice. If you do decide to treat clover as a weed, it is best treated with a post-emergent herbicide applied locally to spots where the clover appears.
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Keeping weeds away from your lawn
Weeds and other undesirable intruders fall into three categories: annuals, perennials, and coarse weed grasses.
Annual and perennial weeds
Annual weeds often pop up in newly sown lawns, and usually disappear with mowing. Perennial weeds are a bigger problem. They’re not usually eradicated by mowing, which means you have to treat them with a weedkiller. Never apply weedkiller to a new lawn. Give your lawn nine months of growth before you apply the weedkiller.
Coarse weed grasses
These are the toughest weeds to eradicate. Selective weedkillers are ineffective because the weed grasses have similar characteristics to your lawn grasses. The only effective way to get rid of them is to cut out the roots with a sharp-pointed knife.
Tips for growing a weed-free lawn
No matter how well you prepare your site, some weeds will always appear. Don’t rush to sow your lawn. Leave the seedbed fallow for a few weeks. This gives many of the weed seeds a chance to germinate. You can then remove or destroy them before you sow your lawn.
In the early stages of a new lawn, you can pull out most weeds by hand. But take care not to disturb the tender grass seedlings. You can also cut out weeds with a sharp-pointed knife.
You can treat an established lawn with weedkiller anytime from May to September, but not when there’s a drought. The weedkiller will be ineffective on the weeds and may scorch your lawn.
Grass seeds to help you avoid weeds
A modern grass-seed mixture, such as Turfline® GrassFix, gives you a dense, durable lawn with the ability to compete strongly against weeds. Adding Microclover® increases anti-weed competition even further and strengthens the grasses in your lawn.
Using Pre-Emergent Herbicides the Right Way to Kill Your Lawn’s Weeds
There’s a secret to tell. Using pre-emergent herbicides the right way will kill your lawn’s weeds.
Okay, it’s not a secret. But it seems that too many homeowners stare angrily at sprouting patches of crabgrass or tear their hair out when dealing with summer weeds like dandelions.
In this story, we’ll walk you through one of the two major classes of weed-killing chemicals — pre-emergent herbicides. You spread or spray pre-emergent products on your lawn, taking the fight directly to weed seeds before they can grow.
What is a Pre-Emergent Herbicide?
According to North Carolina State University, pre-emergent herbicides are chemicals that prevent weed roots, shoots, or both from establishing.
What does that mean? It means that pre-emergent herbicides don’t actually kill weed seeds before germination.
Instead, they fatally interrupt their growth process in some way (often it’s in the cell division stage) to prevent the seed from getting all the way through the seed germination stage.
For that to work, it has to be in the soil at the right time — at the right temperature.
(If you already see weeds in your grass, see our discussion of the other major class in the story “Applying Post-Emergent Herbicides to Your Lawn.”)
Pre-emergence herbicides form the backbone of weed control programs,” says the University of Georgia Extension Service’s guide to weed control. “They do not control all weeds that may be present in a lawn, but they are effective for many of the most common lawn weeds.”
When to Apply Pre-Emergents
“The soil temperature (not air temperature) should be in the 50-55 degree range,” says Dr. Rebecca Grubbs-Bowling, assistant professor and turfgrass specialist at Texas A&M University and author of “A Homeowner’s Guide to Herbicide Selection for Warm-Season Turfgrass Lawns.”
Because climates vary, application dates will be different depending on where you live.
Spring Application: When the Soil Warms
Exactly when your soil turns that temperature will depend on your local climate, and what the weather is like this season. Mid-winter? Early spring? Late spring?
For example, with crabgrass (and its summer annual brethren such as foxtails, goosegrass, and barnyard grass), a pre-emergent can be applied as early as January in Florida, but in Michigan, homeowners might utilize a spring application.
You can find localized soil temperature readings online or from your county’s Extension Service. For the most localized data of all, plunge a gauge into your own turf.
Simple soil temperature gauges can be found online or at garden shops for $8-$15. A meat thermometer with a 3-inch probe will serve the same purpose.
Grubbs-Bowling says pre-emergent weed preventers are best suited for grassy weeds and annual weeds that reproduce by seeds. “They don’t work as well on perennials.”
Annual weeds are either winter annuals or summer annuals. When to use pre-emergent will depend on the weed type.
Summer Emergent Applications
Chickweed, filaree, and poa annua (annual bluegrass) are among the weeds that germinate in winter and have a delayed growing season in spring.
For them and other winter annuals, a second application of pre-emergence herbicide in early to late fall or early winter — depending on your climate — will prevent them from taking hold. Applying pre-emergents when the soil temperature is 70 degrees is ideal.
They’ll kill clover seed, too, but you may not want to: Clover is making a comeback as a nitrogen-rich, pollinator-friendly companion for lawns.
How to Apply Pre-Emergents
Now that you know when to apply the pre-emergent, you’ll need to measure your lawn and determine how many square feet of product to purchase.
Then, you need to know how to apply it, which will depend on the type you choose. Choose between granular and liquid–which is an entirely personal preference.
How to Apply a Granular Pre-Emergent Herbicide
- You’ll need a spreader to spread the granules.
- Read the label thoroughly.
- Calibrate your spreader based on the label recommendations and then fill your spreader.
- Next, using your spreader, apply the granular pre-emergent as evenly as possible.
How to Apply a Liquid Pre-Emergent Herbicide
- For this job, you’ll need a sprayer.
- Most liquid pre-emergents come with a sprayer, but they can also be purchased in various sizes and styles.
- Next, mix the product according to the label. Not following this step carefully can lead to product ineffectiveness or a damaged lawn.
- Then, spray the pre-emergent evenly and systematically, row by row, just as you would mow your lawn.
Note: No matter which pre-emergent you choose, it will need about 1 inch of water to activate. Irrigate 3-5 days after application.
How to Choose Pre-Emergent Herbicide
Here are some things to consider before choosing a pre-emergent herbicide:
Selective vs. Nonselective
- Selective herbicide: Formulated to kill certain kinds of weeds and leave other plant life alone, or at least not damage your grass so much it can’t recover.
- Nonselective herbicide: Will kill everything it touches — including your grass, flowers, and plants. It’s highly effective, just be careful when applying.
Most of the herbicides you’ll find at the garden center are going to be selective, but choose carefully.
Which Weeds Will It Kill?
Not all pre-emergent herbicide applications will kill all types of weeds. For example, selective herbicides made to kill broadleaf weeds will not kill the dreaded crabgrass — because it’s a type of grass.
- Herbicides that contain isoxaben, simazine, or oxyfluorfen, for example, kill some broadleaf weeds but are ineffective against others and against invasive grasses.
- Herbicides with the active ingredient dinitroaniline, napropamide, metolachlor, and dichlobenil will kill invasive grasses and some – but not all – broadleaf weeds.
Other popular pre-emergent chemicals include:
- Prodiamine: The active ingredient found in the popular Barricade brand pre-emergence herbicide, which tackles about 30 different broadleaf and grassy weeds, including the dreaded crabgrass and annual bluegrass (poa annua).
- Oryzalin: This chemical is used in Surflan and several other brands as a broadleaf weed killer and is also effective against spurge. In turfgrass, it gained popularity for pre-emergent weed control on established, warm-season turf.
- Dithiopyr: Effective on about 45 grassy and broadleaf weeds, Dithiopyr is the active ingredient in Dimension and several other brands. It is one of the few pre-emergent lawn care products that have some effectiveness against weeds that have already sprouted. But it needs to be used at maximum strength for that to happen. Effective for about four months after application.
A natural option: Corn gluten meal is a chemical-free pre-emergent that prevents weeds from sprouting about 70% of the time.
Granular vs. Liquid Pre-Emergent
This is a matter of personal preference. Here are a few things to consider when choosing granular vs. liquid pre-emergents.
- Liquid pre-emergent products must be mixed carefully while granular does not.
- Liquid requires a little less labor. You just have to spray, and move as needed to reach your entire lawn. Granular herbicide requires you to walk the entirety of your lawn with the spreader.
- Liquid is easier to distribute evenly than granular.
- Granular needs more water to become active than liquid.
- Granular is easier to apply for beginners.
- Granular is typically cheaper.
Whichever product you select, it’s vital to apply it thoroughly and evenly to gain the best weed prevention.
A pre-emergent must cover your target area completely to serve as a barrier against weed growth. Missing a spot could mean trouble because if you give a weed an inch — it’ll take a yard!
Read Labels Thoroughly
By law, herbicide labels must contain specific information on the ingredients, proper application, and dangers of the product. Although it’s hardly provocative prose, read the labels thoroughly.
“People just don’t read labels,” says Karey Windbiel-Rojas, a pest management specialist with the University of California. In her community outreach programs, she stresses the importance of reading and understanding labels.
Don’t Expect Miracles
Don’t expect a miracle. You will not kill all your weeds. The herbicide will not reach all the seeds buried in the soil, and weed seeds can sit dormant for years. Others will arrive by air in your lawn, sprouted from weeds from your neighbor’s yard or a random patch of weeds miles upwind.
“If you have soil and sunlight and water, weeds are going to grow,” Windbiel-Rojas says.
Selective herbicides are ineffective on unwanted perennial grasses which will continue to grow through the winter. The old hoe and spade is the best solution for those.
Weed control does not deliver instant gratification.
“Be realistic and reasonable,” Grubbs-Bowling says. “The best defense against weeds is a healthy and competitive yard.”
Proper watering, fertilizing, aerating, and mowing make your yard competitive in the war on weeds – along with patience and persistence.
For more weed information, check out our comprehensive “Guide to Weed Control in Your Yard.”
FAQ About Pre-Emergent Herbicides
Some herbicides can hurt your grass. Pre-emergent herbicides can damage new lawns and shouldn’t be used until the grass has settled in for a few months.
Products containing dicamba can damage St. Augustine and carpetgrass if applied at the wrong time. Also, methylated seed oil, often used in treating crabgrass, should never be used on St. Augustine, carpetgrass, Bermuda, or centipede grass.
Pay particular attention to the label of the pre-emergent product if you have a new lawn, or intend to reseed. If you pick a variety that kills grassy weeds, likely it will kill any new desirable grass seed as well. Most pre-emergence products lose effectiveness after about six to eight weeks, so wait at least that long before reseeding.
For more seeding information, check out this overseeding guide.
Your pre-emergent, especially granular, will need about an inch of rain or water to activate. However, too much rain will dilute or wash away your herbicide. Before you apply, check your local weather forecast.
Homeownership is wonderful. From having your own four walls to planning your outside space as you see fit, your home is yours. But It’s not all butterflies and rainbows. Maintenance is probably the most important aspect of keeping your home the way you want it, but it’s also the most time-consuming and daunting.
But you can check off one of those many to-dos with a little professional help. There are many local, experienced, highly rated lawn care specialists in your area that will take that burden off your shoulders, so you can lie back and enjoy your outdoor space without breaking a sweat–or the bank.
For a free and easy quote, call or click today. Whether you are looking for information or to hire a professional now, we’ve got you covered.
Lynn Walker has been writing for radio, TV and newspapers for more than 50 years, and has expertise in news, features, humor, history, weather, genealogy, science, archaeology and government.
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