Homemade Weed Killers

DIY Weed Killers 

Social media is full of recipes claiming that vinegar, table salt, dishwashing detergent, and a variety of other household items make a “safe and natural” weed killer. The problem is that “natural” does not automatically mean harmless. These mixtures can destroy or knock weeds back, but they can also damage soil structure, disrupt soil biology, and make nearby plants struggle. In other words, a pantry-based weed killer can cause more long-term damage to your property than the weeds ever will.

It sometimes seems that social media has convinced people that if an ingredient sits next to the sourdough starter in a kitchen pantry, it must have been personally approved by Mother Nature. Unfortunately, homemade weed-killer mixes can act like highly destructive, non-selective herbicides. They may burn off top growth, but they often fail to kill deep-rooted weeds, especially plants with taproots.

Pantry items and others in the cleaning cupboard all have a purpose, none of which were intended or designed for use in your garden.  Photo by Annie Spratt

Before you fill your plastic spray bottle with "pantry magic" and apply it enthusiastically around your yard like an eco-warrior, let’s re-examine basic high school chemistry and see what happens when you substitute science with "trust me, bro" biology.

Homemade weed killers are often shared via social media. Are they really “safe” and “natural”? Photo by Andrej Lisakov

High School Chemistry for Present Day Common Sense

Everything is made up of chemical elements and compounds. You, me, soil, cleaning solutions, salads, condiments – we’re all a gloop of chemicals in a meat sack, garden bed, bag or bottle.  The premium compost you purchase is a decaying, crumbly mess of carbon compounds contained within a plastic bag that itself is made up of chemicals; all of which is absolutely fine! It was prepared for use in your garden and is enormously beneficial to the soil and the plants which it nourishes.

Similarly, DIY “natural” weed-killer recipes are also mixtures of chemical compounds that were not designed or intended for use in your garden. Used individually or together, those ingredients still have chemical effects in the garden, and the results may not be what you expected. If you ask any gardener whether they would be keen on spraying acid on their plants and garden, they’ll probably look at you as if you’ve grown a second head. Yet, that’s what vinegar is – acid (specifically acetic acid)!

Many DIY weed killers are touted as “chemical-free”, a statement that shows a profound lack of understanding about what chemicals are. Photo by Getty Images

The Ingredients

These are some of the chemicals that I have seen people encouraged to use in their DIY weed killer.  

Vinegar is Acetic Acid (CH₃COOH): Household vinegar is acetic acid at about 5% dilution, while horticultural or industrial-strength vinegar can be much stronger. When used in gardens rather than a vinaigrette, acetic acid works mainly as a contact herbicide. It damages the plant’s protective waxy cuticle, causing exposed leaves to dry out and wither. It does not reliably move down into the roots (translocate), so deep-rooted weeds such as dandelions will probably regrow after the top growth is burned off.

If I were to ask you whether spraying acid on your garden was a good idea, would you say “Yes”? Photo by Zuzana Rainet

Table Salt is Sodium Chloride (NaCl): Plain old table salt is a powerful desiccant that pulls moisture out of cells through osmosis. Unlike vinegar, which breaks down relatively quickly, sodium chloride can remain in soil until water moves it away. That movement can carry dissolved salts into nearby soil or waterways, creating problems far away from the weed you were trying to kill.

In ancient times, “salting the earth” was a symbolic curse to ensure land remained barren and unlivable. The clearest early written record is in the Book of Judges (9:45), which describes the Israelite leader Abimelech capturing the city of Shechem, killing its people, tearing it down, and sowing the land with salt. Photo by Jason Tuinstra

Rubbing Alcohol is Isopropyl Alcohol / Ethanol (C₃H₈O / C₂H₆O): Social media enthusiasts have been known to suggest adding alcohol to homemade weed-killer mixes, but they rarely explain why. Alcohol can dry and damage plant tissue, and at high enough concentrations it can also harm microorganisms it contacts, like the ones in your soil. That makes it a poor choice for weed killing, especially when the goal is to protect soil life rather than sterilize whatever the mixture touches.

Alcohol is often used in hand sanitizers to kill ‘germs,’ but it is an indiscriminate killer in a garden. Photo by Getty Images

Detergents: Dishwashing liquid lowers surface tension, helping the homemade mix cling to leaves instead of sliding off. That makes the vinegar and salt more effective at burning foliage, but it does not make the concoction safer for soil, insects, or nearby plants. Adding a surfactant from beneath the kitchen to help keep horticultural oils like Neem Oil emulsified whilst being used is practical. In small quantities, adverse effects are negligible, but if the goal is an eco-friendly weed solution, using a certified biodegradable or castile soap is a truer eco-friendly alternative.

A few drops of detergent in a spray is an effective surfactant, and castile soap is an eco-friendly option that does not contain synthetic chemicals. Photo by Margaret Jaszowska

• Epsom Salts (MgSO₄⋅7H₂O): Ironically, magnesium sulfate (aka Epsom Salt) is a component of fertilizer (congratulations, you are feeding the weeds). 

• Baking Soda (NaHCO₃): Baking soda (sodium bicarbonate) is highly alkaline and can violently disrupt soil pH.

• Bleach (NaOCl): Kills weeds and fungal diseases, but will also severely damage your soil, poison nearby plants, and leave toxic chemical byproducts behind. When used with other ‘ingredients’, spraying the concoction atomizes the liquids into a fine mist, immediately triggering dangerous chemical reactions in the air before the droplets even land on the soil. In addition to being a concern for your own wellbeing, it can also instantly kill bees, butterflies, and beneficial ladybugs.

• Hydrogen peroxide (H₂O₂): Scorches foliage on weeds but also kills beneficial microbes in the soil and – if it gets near the roots of plants you want to keep – can burn the feeder roots, stunting their growth and even killing them.

Before you use random items in a DIY weed killer concoction, doing an online search to see what they ar, what they become when combined, and their impact if used in a garden is recommended. Photo by Melvyn Swingler

What Happens in the Soil? The Real Damage

Misusing pantry items and household cleaners can do a great deal of harm by turning a thriving microbial community into an acidic wasteland. 

Soil health is critical to garden health. Photo by Tsuyoshi Kozu

Rubbing alcohol and detergents do not distinguish between helpful organisms and unwanted ones. They can harm beneficial soil bacteria and mycorrhizal fungi that plants rely on to absorb nutrients. Repeated use may reduce the soil life that helps plants stay healthy, while creating conditions that are less friendly to the garden you are trying to protect.

When efficient grease-cutters come into contact with soil, they can strip protective coatings from small soil organisms and beneficial insects, increasing the risk of dehydration and death. Over time and with repeated use, these detergents can adversely affect water movement through soil and may also suppress some beneficial microbial populations.

Sodium chloride (salt) splits into sodium (Na⁺) and chloride (Cl⁻) ions. Sodium destroys soil structure, which can turn healthy loam into a compacted concrete block that water can no longer penetrate. Even worse, excess salt in soil raises the osmotic pressure, physically preventing neighboring plants—like your prized tomatoes or hydrangeas—from absorbing water. Sprinkling (or spraying) just one tablespoon of salt over a 1-square-foot patch introduces a concentration of roughly 1,000 parts per million (ppm). Anything over 200 ppm is toxic to standard garden plants. You have essentially built a localized, miniature version of the Dead Sea … and then wonder why your roses are dying. 

The Myth of "Pantry Safe" 

The online defense for DIY weed killer recipes usually boils down to: "If I can put it on my salad, or clean my kitchen with it, it must be safe for the garden!"

This logic is risky. Nature does not care whether something came from the kitchen, the laundry room, or the garden shed. Many common household products can become dangerous when mixed without understanding the chemistry:

• Bleach + Vinegar = Chlorine Gas

• Bleach + Ammonia = Chloramine Gas

• Bleach + Rubbing Alcohol = Chloroform

• Hydrogen Peroxide + Vinegar = Peracetic Acid

Chemical safety isn't a corporate conspiracy; it’s a reality straight out of the periodic table. Just because items are stored in plastic bottles under your sink or next to your spice rack doesn’t mean they’re harmless. 

Using homemade weed killers may have undesirable results. Photo by Getty Images

Truly Non-Toxic Alternatives 

If the goal is to manage weeds without leaving a toxic chemical footprint in your soil, start with methods that physically remove, smother, or burn the weeds, such as:

• Boiling Water

• Flame Weeding

• Manual Extraction

• Sheet Mulching

Better on Fries

Mixing household cleaners and pantry items into homemade weed killers can create real safety risks and may not be effective or eco-friendly. Until you have checked the chemistry, the safest place for salt and vinegar is still on fries and crisps, where they can do their best work.

If you want an “organic” spray option, professionally formulated organic contact herbicide and bioherbicides exist. If you are looking for one, the Organic Materials Review Institute (OMRI) is a useful place to start because it lists products that have been reviewed for use in organic production. Their website is: https://www.omri.org/

Photo by Zoshua Colah