Does Lawn Fertilizer Kill Weeds? (Greenkeeper’s Guide)

Every gardener knows how challenging it is to keep a lush, green lawn. But it can prove even more difficult to keep weeds off your turf. Luckily, a lawn fertilizer can indirectly help you control weeds while enriching your lawn grass.

Lawn fertilizer doesn’t kill weeds. Its primary function is to supply the soil with nutrients for the growth and development of lawn grass. While fertilizers don’t kill weeds directly, a well-mowed, watered, and fertilized lawn will eventually choke out weeds, making them disappear over time.

In the rest of the article, I will explain how you can use lawn fertilizer efficiently to keep your grass healthy while keeping the weeds under control. I will also share alternative ways to prevent weeds from taking over your lawn.

How Can Lawn Fertilizer Help Control Weeds?

Lawn fertilizer is essential for lawn grass to thrive in any kind of soil. Grass feeds heavily on soil nutrients, such as nitrogen, phosphorus, and potassium, requiring gardeners to replenish them during the growing season. Otherwise, your lawn grass will quickly be taken over by weeds.

Weeds are very competitive plants that can easily outgrow others because of their aggressive growing traits and reproductive behavior.

The Downsides of Weeds

Below are some of their inconvenient qualities:

Rapid Growth

For one, weeds are fast-growing. Weeds grow quickly and aggressively, making it easier for them to crowd your garden and choke out other plants, such as your lawn grass.

Can Grow Nearly Anywhere

Weeds can also adapt to various substrates. These pesky plants can grow even in rocky or clay soil. If you have pebbles or rocks in your garden landscape, you might find some weeds creeping through the gaps.

Tolerate Poor Soil

Weeds are tolerant of poor soil conditions. As your regular plants struggle with several soil issues, such as compaction and nutrient depletion, weeds tend to take advantage of the situation and outgrow your plants.

Possible Re-Growth

Weeds can reestablish themselves when not uprooted. Weeds are inconveniently resilient. They can grow back quickly enough as long as their roots are intact.

This is especially true for perennial weeds with deep taproots.

Long-Term Survival

Weed seeds can survive in the soil for several years. Weeds can stay dormant and wait for the conditions to become favorable enough for them (i.e., when the lawn grass becomes weak or when the seeds are brought up to the germination zone due to tilling).

When you see weeds growing abundantly on your lawn, it is usually a sign that there is something wrong with soil conditions, general lawn care, and nutrient balance. Weeds also thrive in areas not covered by grass. 

With this knowledge under our belt, let’s break down how the right kind and amount of lawn fertilizer can help control weeds.

Organic Lawn Fertilizer Can Improve Soil Quality and Texture

One of the reasons lawn grass struggles against weeds is due to poor soil quality and texture. As discussed, weeds don’t mind dense and nutrient-poor soil. As a result, they will steal what few nutrients are present in the ground and crowd out your weakened grass.

Several factors can reduce the quality of your soil, making it unsuitable for your grass to survive and conducive for weeds to take over.

Some of these factors are:

  • Foot and wheel traffic that compacts the soil
  • Heavy rain or poor watering practices
  • Thatch buildup from poor mowing practices

Using organic fertilizers like compost can improve soil quality. They can help aerate the ground enough for the roots of your turfgrass to breathe. In addition, an improved soil texture can also relieve compaction that prevents adequate drainage.

Organic fertilizers also feed your lawn grass with enough nutrients necessary for them to thrive. With better aeration, drainage, and nutrients, your grass will be revitalized and have better chances to compete with weeds.

Lawn Fertilizers Can Enrich the Soil

Lawn grass needs regular fertilizing to replenish the soil with enough nutrients for the growing season. Without sufficient nutrients, your grass will become weaker and more susceptible to diseases, reducing its ability to compete with the aggressively growing and disease-resistant weeds.

It’s important to note that weeds can also benefit from the added nutrients in the soil. However, provided you keep your weeds under control through manual management like hand weeding and mowing, they shouldn’t grow fast enough to compete with your grass.

The key is to time your fertilizing schedule appropriately to ensure only the grass will benefit from the additional nutrients. Regular fertilization will lead to a thriving lawn with fewer weeds over time.

Lawn Fertilizers Boost Grass Growth

Lawn fertilizers can help speed up the growth of your lawn grass, leaving weeds with fewer opportunities to keep up. As a result, your lawn grass will grow beautifully while the weed seeds remain underground.

Professional fertilizer does not necessarily encourage weed growth. From my experience, the grass gets a boost after fertilizing, while weeds stay behind. Maintaining a good fertilizing and weeding routine will eventually eliminate the weeds in your lawn.

Things To Consider When Managing Weeds on Your Lawn

Now that I’ve explained how you can use lawn fertilizers to prevent weeds from taking over your lawn, there are a few things you need to consider when applying them:

Fertilize Your Lawn After Manually Removing the Weeds

To manage weeds more effectively using lawn fertilizer, you must couple your efforts with weed removal. Removing weeds by hand or uprooting them using tools like a weeding knife will reduce their chances of growing back.

Most fertilizers will also provide nutrients for the established weeds, so it helps to remove visible and overgrown ones before fertilizing your lawn. Moreover, you wouldn’t want your lawn fertilizer wasted on weeds.

For spot removal, I recommend using a weed puller like the Walensee Weed Puller (available on It has a long handle that allows you to pull weeds quickly and conveniently while walking around your lawn. 

Don’t Overfertilize Your Lawn

As I mentioned, lawn fertilizer does not kill weeds, so there’s no point in overfeeding your lawn with fertilizer. Even if you’re worried that weeds might compete with your turf grass for nutrients, overfertilizing your lawn will only prove dangerous.

Lawn grass may suffer from fertilizer burn when fed with too much fertilizer. The excess nutrients may also leach deep into the ground, contaminating nearby bodies of water. Always check the product label for the recommended dosage and prepare half that amount to be on the safe side.

Ensuring that your soil is well-aerated and has good drainage and moisture retention is often enough to keep your lawn grass healthy and the weeds at bay.

Be Cautious With DIY Weed Killer Solutions

It’s easy to understand why numerous gardeners resort to DIY and homemade solutions when dealing with weeds in their lawns. Many pieces of anecdotal claims are available online, vouching for the effectiveness of such materials.

However, what works for them doesn’t always apply to everybody. Various factors must be considered before trying out these methods. 

Here are some popular alternative methods people use to kill weeds in the garden:

Using a Vinegar Solution

Various turf grass species have specific soil pH requirements, so it’s somewhat risky to use acidic substances to kill weeds.

The effectiveness of regular culinary white vinegar in killing weeds is highly dependent on its acidity and volume. However, it is a weak acid and may have detrimental effects on your soil and grass when applied in high volumes.

Using highly acidic horticultural vinegar can be dangerous for you and your lawn grass. Such chemicals cannot distinguish between your grass and the weeds you want to eliminate.

Using Bleach

Some gardeners claim they’ve had some success using bleach to manage weeds. However, it’s not the best way to deal with weeds on your lawn. This solution can indiscriminately kill weeds and grass, leaving your lawn with yellow and dead patches.

After some time, these bald spots on your lawn will be filled in by new weeds—some varieties can spread through stolons or seeds that can be easily blown by the wind.

Be Mindful When Using Herbicides

Many products in the market will help kill weeds while proving safe for your lawn grass. Herbicides like Tenacity or Roundup will work magic, but they must be used carefully, both for the environment and your personal health.

If you’d like a visual demonstration of how to use herbicides to kill your weeds and not your grass, here’s a helpful video:

It’s essential to remember that while the herbicides won’t kill your grass, some chemicals may stay in the leaf blades. You might as well avoid adding the herbicide-treated grass clippings to your compost pile, especially when you plan to use that compost to feed other plants in your garden.

Some herbicides can stay active anytime between 30 days and several years, so you must also consider proper ways to dispose of clippings from herbicide-treated turfgrass.

On rare occasions, some weed varieties have developed a resistance to some herbicides they used to be sensitive to. Carefully follow the instructions regarding the appropriate dosage and application procedure to achieve optimum results.

If you want to learn more about other ways to effectively manage weeds in your garden, check out the article I wrote on the subject: How to Make A Garden Weed Free (10 Methods)

Other Ways to Suppress Weeds on Your Lawn

In addition to adding appropriate and adequate amounts of fertilizer to your lawn, you can help suppress the weeds with the following tips:

Water Your Lawn Adequately

Many lawn grass varieties are drought-tolerant. However, it’s best to still feed them with adequate water, as weeds tend to be more tolerant and competitive than your grass.

If your grass is exposed to a stressful environment, it will have less tolerance to drought, allowing the weeds to easily take over your lawn.

One way to keep your lawn grass healthy is to feed it with enough water, especially during hot and dry conditions. Many lawn fertilizers also need adequate moisture to work their way into the ground and become more accessible to the roots of your lawn grass.

Interestingly, some weeds have long taproots that can access moisture deep below the surface. In contrast, others have lateral roots that can access water close to the surface. Regardless of the type of weeds you have creeping into your lawn, your grass will likely have competition for moisture

Ensuring that your grass has enough water and pulling out weeds as soon as you spot them will help maintain your lawn’s health.

Mow Your Lawn Regularly

Mowing regularly and keeping the grass and the weeds short will create an uncomfortable environment for weeds.

Cutting the tips of dull or drying leaf blades can help revitalize your grass and encourage them to grow more densely. It will also allow their roots to grow deeper or spread wider into the ground and gain better access to moisture and nutrients.

When that happens, weeds will no longer steal as much water from your grass. Moreover, thicker grass will block the sunlight from getting to the weed seeds underground, preventing them from germinating.

Leaving the grass clippings on your lawn will also allow them to serve as mulch and prevent weed seeds from gaining access to the soil.

However, you must consider the following when mowing your lawn to avoid causing more harm than good:

Avoid Cutting It Too Short

Don’t cut your grass too short. Mow your lawn at the appropriate height, depending on the grass variety. Otherwise, your grass will feel stressed and weaker against weeds.

Ensure the Mower’s Blades Are Sharp

Inspect the sharpness of your lawn mower blades. Sharp blades will cut more cleanly, reducing the risk of microbial infection.

Mow at the Right Time

Choose an appropriate time for mowing your lawn. You can mow your lawn weekly during the growing season in spring, but avoid doing so immediately after the rain or your watering schedule. Allow the grass blades to dry before mowing.

You can also mow your lawn a few times in summer to help your grass breathe but don’t cut it too short to prevent weed germination.

Remove Long Grass Clippings to Prevent Thatch Buildup

Many experienced gardeners recommend leaving the grass clippings on your lawn after mowing, allowing them to decompose and provide your soil with more nitrogen for better lawn health. This is an excellent recommendation when done right.

If you’ve mowed a lawn before and decided to leave the glass clippings behind, you must have noticed how they create thatch as they dry up. This is especially true for very long blades.

Grass clippings can help keep your soil cool in the summer and improve moisture retention. However, too much can reduce aeration for the roots and ultimately choke your grass.

It’s also worth remembering that grass clippings can take about a month to decompose when left on your lawn. For these reasons, you should leave only short grass clippings behind. Ideally, they should be less than an inch (2.5 cm) long.

If you’ve let your grass grow too long and the mowed tips are longer than an inch (2.5 cm), you might as well rake them and dispose of them properly. Otherwise, they will build up thatch and encourage the growth of moss, which can present another problem.

Check the Soil pH and Nutrient Levels Regularly

As explained, soil nutrients deplete over time as your garden plants and lawn grass consume them. The loss of nutrients in the soil can also influence pH, affecting how well your grass can continue to thrive.

Checking your soil quality and nutrient levels at least once a year is crucial to maintaining a lush, green lawn. You can use home test kits to check the soil pH. However, for more accurate results, you can collect several samples from multiple spots on your lawn and send them to a laboratory or a nearby cooperative extension.

That way, you can identify what nutrients are lacking in your lawn and formulate the right kind of fertilizer. It can also give you an idea of how frequently you must fertilize your soil and what amendments to use to improve the quality.

Treat Infections Before They Get Worse

Some weeds are resistant to microbial infections that affect common crops and lawn grass. They can also carry harmful microbes and spread them to susceptible plants. If your lawn has bald and yellowing spots, it can indicate that a soil pathogen has infected your grass. 

You must treat the infected area right away to prevent the spread of the disease. Otherwise, your lawn grass will become weaker, and weeds will take advantage of the situation.

For fungal infections, you may need to send a sample of the infected patch to a laboratory for accurate diagnosis. Identifying the exact fungus causing the disease will help you select the most appropriate treatment. Remember that specific fungicides don’t work on all fungi, and some diseases may not be curable at all.

Final Thoughts

Although lawn fertilizers cannot kill weeds, you can use them to boost your lawn’s health and give it a fighting chance against its sturdy competitors. A healthy lawn will leave no room for invasive weeds to thrive.

Applying additional care management and weed control methods, such as herbicides and manual removal of weeds, can eventually eliminate the weeds from your lawn.

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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