Certain types of grass may seem “unkillable” and others, the types you want in your lawn, can seem far too delicate for the robust reputation grass has. The thing is, there are hundreds of grass species and dozens of common grass types in the US alone. All of these grass types have slightly different needs.
Below you can learn what exactly it takes to kill grass, including a list of specific substances and practices as well as a number of overlooked factors. Whether you’re looking to eliminate a problem species of grass or searching for answers as to why your lawn is turning brown, this article should help point you in the right direction.
What Kills Grass: The Different Factors that Can Lead to a Lawn’s Demise
As mentioned above, all grass types have specific needs. Some grass types like an acidic pH and can handle a mostly shady environment while others need full sun, a dry climate, and an alkaline pH to thrive. Below are the 9 critical factors that determine whether a lawn lives or a problem grass dies.
Chemicals, including fertilizers, cleaning products like Clorox bleach, and herbicides like Roundup, can all have very potent effects on grass, even in small quantities. These effects range from the ability to cause chemical burns, limit or halt the uptake of nutrients, disrupt the photosynthesis process, and the ability to halt growth and repair processes.
Synthetic hormones may be a type of chemical, but they deserve special attention as synthetic auxins (a specific plant hormone related to growth) are the primary component of most selective herbicides. Selective herbicides are the most common types of lawn herbicides. They work by putting out a synthetic hormone (auxin) that causes immediate, unregulated, and constant cellular growth in certain types of plants. These are most often broadleaf or woody plants.
This sudden growth spurt causes severe damage to plants in two ways. First, it depletes nutrient stores and disrupts the absorption process. Next, the unregulated growth can cause cellular collapse. As this sudden growth spurt occurs at the cellular level and leads to death so quickly, it is almost impossible to see with the naked eye.
Grass, like most plants, needs quite a bit of light to survive. This light is used in the process of photosynthesis to create food for the grass. A lack of light will completely halt plant growth and may quickly allow the plant to be compromised by bacteria and other unwanted organisms, breaking down the plant further and leading to its demise.
Like light, water is a major component in the process of photosynthesis. However, water also plays several other roles. It is a critical component in the transfer of nutrients throughout the entire plant as well as a necessary resource for normal growth and the dilution of unwanted substances in the soil, plant, and root system.
Small microorganisms, deer, and grubs are all-natural enemies of healthy grass. While damage from large animals can be easy to see, grubs and other underground pests can disrupt a patch of grass from the soil up, leaving many lawn owners wondering why there are sudden brown patches in their lawn.
One major factor in the health of a lawn is aeration. As a lawn is walked over, rained on, or even driven over, it can become compacted. This means that not enough air or nutrients from the air are being exchanged with the air trapped under this compacted soil.
How well-aerated soil is can even determine how well it can absorb water. If the ground is repelling water or water runs off instead of being absorbed, the soil may be compacted. Though this can lead to the death of grass, it’s also a deadly condition to all plant life and even insects and microorganisms in the soil.
Though most lawn grasses are hearty and capable of making it through a given winter in the area in which they are planted, some can be more sensitive to sudden changes in temperature than others. Further, all grass is susceptible to extreme temperatures. For example, no species of grass can survive being submerged in boiling water.
The alkalinity or acidity of soil can also be one of those things many people don’t think about until things start looking dire. Yellowing grass is a frequent sign of an incorrect pH for that grass type. The pH of the soil can affect the rate of nutrient absorption, root length, and overall plant vigor.
Further, some problematic grass species have a very different pH preference than that of many desired lawn grasses. Changing your lawn’s pH can be one of the easiest and longest-lasting ways to kill unwanted grass seeds and help your lawn thrive naturally.
Speaking of nutrients, having the right things available in the soil may be one of the single best ways to keep a lawn healthy and avoid problems. Though there are dozens of necessary nutrients for all grass types and it can be a challenge to keep track of them all. It may be easier to keep track of the things that can disrupt nutrient production or absorption.
For example, if salt builds up in the soil it can prevent plants from absorbing nutrients and the water grass needs to survive. This can also lead to stunted root growth and, further, longer and longer recovery times after mowing.
Specific Substances that Will Kill Grass
From commercial herbicides to household cleaners and even some common pantry staples, most people have access to dozens of grass-killing substances. Sometimes you can use these to kill grass and sometimes you accidentally spill them and they might kill your grass. Either way, below are 18 different substances that answer the question, “What kills grass?”
Household bleach, Clorox or otherwise, contains chlorine. This is what gives it that distinct “bleach” smell. While chlorine can harm grass if applied directly, there isn’t all that much chlorine in a bottle of bleach.
What really makes bleach deadly to grass is its high pH. Bleach, or sodium hypochlorite, has a pH of 12 or more. This means that bleach is highly corrosive and can cause chemical burns to plants on contact. Bleach also prevents grass and weed seeds in the affected area from germinating in the future.
Lemon juice is a common pantry staple. Whether it’s freshly squeezed or from concentrate, as long as the lemon juice in question is “natural strength” or better, that lemon juice can be applied to any plant as a natural herbicide.
Lemon juice is acidic and will remove the outer waxy coating of a plant’s leaves and stem. This allows the plant to dry out very quickly as it will be unable to retain moisture.
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Copper sulfate may be meant for killing smaller organisms like moss and algae on pasture and golf courses, but this is one of those substances where a little goes a long way. 1 oz of copper sulfate in a single gallon sprayed over 250 sq. ft. won’t kill your grass, but 3 oz in that same gallon will.
Once applied, the plants will, over the course of as little as one week, show evidence of copper poisoning. Roots will die off and plants may even look like they are beginning to rust with orange and red spots developing on all affected grass and other plants.
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Landscape fabric is often used to kill grass but it does have quite a few drawbacks. Certain types of grass, like crabgrass and Bermuda grass, will colonize landscape fabric in as little as 3 days if not pulled out as soon as they take hold. Most types of turfgrass, however, are easily smothered by landscape fabric and a thin layer of rock or mulch.
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Preen is a pre-emergent herbicide that kills grass seeds and very early sprouts by using chemicals that prevent seeds from sprouting and slows nutrient uptake in young plants. The tender plants emerging from a new rhizome may also be damaged by Preen. Preen can also damage the health of the soil and lead to future problems if used on an established lawn and, as such, Preen does not recommend itself for use on lawns.
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Human urine may be a potential nutrient source for plants, but it is so strong in this nutrient supply that it can cause a plant to “burn” when it attempts to take up these potent nutrient stores. Luckily, human urine is easily diluted and any grass that has accidentally been burned by human urine is easily overtaken by neighboring plants.
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Pine-Sol is a detergent that, like dish soap and other household detergents, will break down the waxy, oil-based outer layer of plant leaves, stems, and other components. This, combined with the sodium carbonate found in Pine-Sol, will make it difficult for grass to retain moisture, prevent germination and cell division, and slow nutrient uptake.
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Muriatic acid is an “impure” form of hydrochloric acid. Like hydrochloric acid, muriatic acid is quick to burn, corrode, and break down most organic cells, including grass. Even if spilled on the ground, muriatic acid can burn plant roots several feet deep in the soil, making this one of the most effective ways to kill any plant down to the root.
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Baking soda or sodium bicarbonate is a common kitchen staple, used to bake quick breads such as muffins and as a last-minute de-icer for sidewalks in the winter. However, sprinkling baking soda is also an easy way to kill grass.
Baking soda particles are phytotoxic, making it difficult for plants to use the sun the way they intend to. This can lead to leaf damage or, in the case of grass, blade damage. This can lead to moisture loss and an inability to make or process certain nutrients. And that’s just where it starts.
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TSP (Trisodium Phosphate)
TSP is an inorganic cleaning agent used in many industrial processes. It isn’t generally approved or recommended for common household use and when it is used for things like power-washing in cases where there is extreme grime buildup, barriers must be used to protect plants.
Like other salts and detergents, TSP will compromise the waxy outer coating of the plant and draw out the moisture within. This damage cannot be repaired. Further, TSP can stay in the plants and soil for a number of weeks, continuing to break down plant life.
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Propylene glycol antifreeze is deadly to plants, even in small doses. Like many other chemicals in this list, antifreeze will corrode the plant’s outer layer and break down the cells and structures within. This can continue for several weeks before the antifreeze has dissipated. Without cleanup, it may be difficult to grow anything for several months in an area where there has been an antifreeze spill.
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Borax is an inexpensive household cleaner that is often used to kill weeds. It will not, however, naturally spare grass. Borax is not a selective herbicide to any degree. Spraying borax solution on grass in too high a concentration will cause the roots of the grass to die back and, eventually, lead to the plant starving.
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Ammonia can be a great lawn fertilizer or an inescapable poison that can not only kill the plants it is applied to but also build up in the soil and harm or kill nearby plant life. When used in quantities this high, ammonia causes damage in two ways.
First, as plants try to take up too much ammonia, it can corrode the pathways needed to take in nutrients as well as block out other nutrients. Next, this corrosion can lead to roots dying off and chemical burns that cause the plant to dehydrate.
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No type of grass is immune to the effects of boiling water. Just like with most other types of living tissue, grass can be “burnt” if boiling water is poured onto it. The high heat will kill each cell it comes into contact with, making it difficult for the plant to maintain basic life functions. If too much of the plant is damaged, it will die.
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Common dish soap is a detergent and will, when applied directly or with a small amount of water, break down the outer waxy coating of each blade of grass. This will lead to moisture loss and the inability to retain moisture once the damage progresses.
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In as little as 30 minutes, grass soaked in gasoline will show visible signs of death. The blades will curl and turn brown. Internally, these grass plants died within minutes of application. Gasoline kills plants quickly by breaking them down and “burning” them from the inside out.
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Diesel is something you don’t want to get on your lawn. If you do have a spill, it’s important to contact your local hazardous waste disposal center for directions on what to do next. Small spills can usually be contained by digging up any contaminated dirt or by also applying an absorbent medium shortly after the diesel has been spilled.
Diesel kills grass and weeds. In the US, it’s illegal to use diesel to intentionally kill plants as the impact diesel can have on soil and water quality can be devastating, even in small amounts.
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Salt water kills plants by way of chemical burns, blocking nutrient pathways, sodium toxicity, and dehydration. Salt, in the quantities found in salt water, is not a healthy thing to feed grass and will build up in the soil over time if it is frequently poured over the same spot, even if the concentration of the salt in the water seems “low enough”.
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Newspaper is cheap or free and is often easy to find in abundance. Newspaper can be used, in thick layers, to smother grass and prevent any sun from reaching it. This causes the grass and any other plants or weeds caught under the paper to die within several weeks, breaking down rapidly. Weed and grass seeds are also often smothered at the same time.
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Atrazine is a broadleaf herbicide used by many commercial landscaping companies to control weeds and unwanted grass growth. It can also be purchased for residential or private use, though it can be tricky to use without unintended results.
Atrazine prevents a plant from generating the energy it needs to grow by interrupting the photosynthesis process. This affects “broadleaf” weeds, or weeds with large leaves as well as several types of grass, including lawn grasses such as Bermuda. It can also blunt or prevent new growth from grass species like Zoysia that aren’t even in the “broadleaf” category.
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Mulch, if used to kill grass, is effective. You just need to make sure you have the right type of mulch for the job. In some cases, you may even want to combine several types of mulch so you can smother grass and weeds where you need to, but also feed your lawn and bedding plants or landscaping at the same time.
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Though the urine of herbivores might seem less intense than that of carnivores, deer are an exception. Not only is their urine highly concentrated but it has the same high potential for damage as coyote or fox urine. Deer are also notoriously difficult to keep off of a lawn, but there are ways to do it. Clattering noises, motion, and flashing lights are the most effective strategies outside of building a fence.
Certain grass types are also less likely to be killed by deer or deer urine. These include Fescue, Zoysia, and all types of ryegrass.
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What Won’t Kill Grass
Below is a list of products that are sometimes found in DIY weedkiller recipes or that may have an unjustified reputation for harming lawns. After thorough research, all of them have been found ineffective at killing grass and easy to use in a lawn-friendly way.
Calcium chloride is the primary component of many ice melting products. It has a low amount of sodium compared to rock salt, the leading primary ingredient in ice melt products. Though the sodium from calcium chloride could build up over time and cause problems. This takes far too much product to be practical and is easily diluted in smaller quantities.
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When used as directed or even in much larger quantities, lime can help adjust the pH of your lawn to better accommodate the species of grass growing there. If the lime is applied too densely, it absorbs slowly enough that there is plenty of time to make corrections before damage is done.
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Castor oil will not kill grass. This is an organic substance that, while not a great fertilizer, will ultimately break down with no ill effects.
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Tordon is a selective herbicide that only kills broadleaf plants. The type of hormones it uses aren’t even effective on seeds or sprouts. As long as the type of grass you have is a “true” variety of grass, Tordon is safe to use on it.
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Triclopyr is another selective herbicide that, though it contains different chemicals and slightly different hormones, works in the same way as Tordon. As long as the “grass” you are applying this product to is a true grass, Triclopyr will not affect it.
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Algaecide, if applied with the recommended dilution, will only harm algae, moss, and other plant-based organisms much smaller than grass. However, many algaecides are copper-based and can build up in the soil if too high a concentration is used or these products are used too often. High copper levels can harm all plants and some animals.
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Spray paint is safe to use on grass unless it is used to purposefully coat all blades of grass from top to bottom on a given plant. This will smother the plant. With the typical application, spray paint should stay on the top half of a blade of grass and will be mown off over time.
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Coffee grounds can be a good source of nutrients for grass, but are rarely harmful unless used to fully smother a patch of grass. While coffee may be acidic and lightly corrosive, used coffee grounds are almost neutral.
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Wet & Forget
Wet and Forget is an algaecide made up of about 10% benzalkonium. While this is an effective product for killing small plants like moss and algae, it’s not effective on grass. Further, Wet and Forget takes time to become harmful. This means that in the case of a spill, a little water applied in the first 8 hours can often prevent all meaningful harm.
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Sawdust, unless applied in a layer so thick it can compact and repel water, is not a great method for killing grass. Sawdust is often too fine-grained to prevent all of the light from reaching the grass beneath.
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Once Oxi-Clean has been exposed to water, it only takes a small amount of time for it to break down. In doing so, you will ultimately be left with oxygen, water, and a little sodium. Unlike chlorine-based bleaches, Oxi-Clean isn’t particularly corrosive and should not harm most plants, including grass.
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The classic formulation of Simple Green is safe for plants of all kinds, even if poured straight from the bottle onto a lawn. All ingredients in classic Simple Green are biodegradable and, at most, may stall plant growth for a few days as these ingredients break down. Water can speed this process along.
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Kitty litter is often clay, silica, or paper-based. These substances are not meant to be harmful to plants or animals. The particles of any of these are also large enough to sweep or vacuum up, in the case of a spill.
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Oxalic acid is naturally found in many plants and is not toxic to grass.
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Crossbow (Brand Herbicide)
Crossbow is another selective herbicide that contains Triclopyr and 2,4-D. Both of these herbicides should leave grass alone while killing all varieties of woody or broadleaved plants through the use of “auxin mimics”.
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Hot Tub Water
Hot tub water is often blamed for killing grass as it contains chlorine. However, allowing the chlorine to dissipate for several hours before draining the hot tub or simply diluting the runoff can save any grass this water comes into contact with.
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Cayenne pepper, though it contains an irritant for most people and animals, is not harmful to plants or even the least bit irritating to them as they have different systems and receptors.
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Similar to hot tub water, pool water should not have enough chlorine in it to harm grass. A small splash should be well tolerated and any larger spills can be mitigated by adding fresh water, or allowing the pool to sit for several days with no addition of chlorine before it is drained.
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The application of vinegar with an acetic acid content of 10% or more could cause mild “burning” or browning to the leaves or blades of grass and even greater damage to broadleaved plants. However, most household vinegars only have a maximum of about 5% acetic acid. This is not strong enough to harm grass.
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Beer is the subject of many a lawn care myth. Is it good for your lawn? How much should it be diluted? Can beer poured on a lawn actually kill fungus? The truth is, beer is not nearly as miraculous a lawn care tool as it has been said to be. Not only will the sugar in beer feed more bacteria than the alcohol could kill, but the sugars in beer are also so simple and refined that your grass can’t even use them as energy.
On the bright side, a little beer spilled on your lawn isn’t devastating and can easily be cleaned up with a few gallons of water and, if it doesn’t soak in too quickly, a towel. Clean-up is important, too. Spilled beer on any plant, including grass, can attract lawn-killing insects like slugs and grubs.
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Rabbit poop in and of itself is rarely harmful to a lawn unless you have a rabbit enclosure on your property. The buildup could also attract predators that may urinate on or dig up your lawn. Rabbits, with how little they eat and how low in nitrogen their droppings are, are some of the least destructive visitors your lawn could have. They are also unlikely to transmit diseases to humans through their feces, though infected rabbits could transmit certain diseases to dogs and cats.
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What Kills Grass and Weeds Permanently
Grass and weeds can be hard to kill permanently and even if you do manage it, seeds in the soil could still spawn new weeds and grass as soon as the current batch has been removed. Below are the best substances to use to kill grass and weeds as well as most if not all of the weed seeds in the soil. However, many of these substances will also make that patch of soil unsuitable for any plant growth for weeks to years.
- Baking Soda
- Dish Soap (Detergents)
- Muriatic Acid
- Copper Sulfate
- Salt Water
What Kills Grass Naturally
Not all substances that can kill grass will leave you with soil that you can or would want to grow something in after that patch of grass has died. Below is a list of substances you can use to kill grass with minimal or zero damage to the surrounding plant life or underlying soil.
- Lemon Juice
- Boiling Water