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.