By Skye Pelliccia, Noxious Weeds Education Consultant, King County Noxious Weed Control Program, spelliccia@kingcounty.gov
So, you’ve found yourself pondering ways to tackle those pesky weeds—perhaps through a friend’s recommendation or some late-night online research. Salt and vinegar might have popped up as the seemingly perfect DIY solution – “eco-friendly,” and you already have some on hand! But before you start sprinkling and spraying, let’s uncover the real story behind these household remedies and their often-overlooked environmental impacts, as well as some possible alternatives.
The Myth of Salt and Vinegar as Safe Weed Killers
The idea behind using salt and vinegar as weed killers is appealing because these ingredients are common household items. The logic goes that if they’re safe enough to eat, they must be safe for the environment, at least safer than synthetic herbicides. Unfortunately, this is a dangerous oversimplification. Both salt and vinegar may kill some weeds, but they do so in a way that can cause significant collateral damage to other plants, the surrounding soil, and the delicate microbiome that supports plant life.
And perhaps this collateral damage would feel ok if these methods were effective long-term, but they are not. Salt, and especially vinegar, act like contact herbicides, meaning they burn the leaves off of plants, with the added misfortune of potentially being harmful to any non-plant beings in the vicinity (worms, beneficial bacteria, fungi, etc.)
Even approved contact herbicides are ineffective for most weeds because they work by killing whatever surfaces they touch, i.e. above ground plant growth (comparable to mowing or burning). For perennial plants and grasses with larger root systems, this doesn’t work well, because the plants will almost always grow back from their roots. This is why systemic herbicides (glyphosate, triclopyr, imazapyr, etc.) are the primary herbicides used in weed control. They work by absorbing into the plant’s vascular system and down into the roots, killing the weed from the inside out versus just on the surface. There are plenty of non-chemical options, but this is just to say that if you’re going to take a chemical approach, there are safer options.
Natural does not always mean good for you and the environment!
When it comes to environmental impact – neither salt (as sodium chloride) or vinegar (as acetic acid) are approved by the U.S. Environmental Protection Agency (EPA) as stand-alone pesticides for pest control. Approved pesticides must undergo rigorous testing and evaluation by the EPA to ensure they are safe and effective when used according to label instructions. This process involves assessing potential risks to human health, non-target organisms (non-plants), and the environment. Approved herbicides have proven to target only plants, usually by attacking specific plant parts at the cellular level, like the chloroplast which animals and other organisms lack. Neither Salt nor vinegar pass this test.
Is it ever appropriate to use these “natural” pesticides?
Sure! Anywhere that you are not concerned about the surrounding soil or plant health, these could work (i.e. gravel lots, sidewalk cracks, etc.). Keep in mind – the efficacy and impacts mentioned below still apply to that area, so please avoid using these options where they are at risk of entering any water bodies (towards storm drains, wet ditches, etc.) or within five feet of any plants you wish to keep healthy.
Vinegar: A Sour Solution
As a weed killer – horticultural vinegar (acetic acid) essentially works as a contact herbicide via acid burns. Vinegar used for cooking and cleaning is often 5% in concentration (95% of this mix is water). Cooking/pantry vinegar is typically made up of 5% concentrate and 95% water. Vinegar that works as a weed killer, by contrast, is anywhere from 20-40% in concentration.
Sour impacts
In addition to short-term effectiveness, acetic acid (the concentrated vinegar) may harm users and the environments they’re treating. While vinegar may offer short-term weed control benefits, its indiscriminate use can have long-term consequences for soil health and ecosystem function. Here’s why:
- Soil Chemistry: Vinegar’s high acidity can alter soil pH, making it unsuitable for many plants and soil organisms. This disruption can negatively affect soil structure, nutrient availability, and overall ecosystem balance.
- Soil Organisms: The acidic nature of vinegar can harm all living things within the microbiome. Vinegar is used broadly to control insects and other pests and could kill other living things in the treated area such as earthworms, fungi, beneficial bacteria, and insects. These organisms play vital roles in a healthy soil system and without them, soils degrade at rapid rates.
- Human Safety: Weed-strength vinegar products are legally required to have product information and warning labels, but unfortunately due to being misrepresented as an “eco-safe option” are often not read with as much caution as synthetic herbicide labels. Reading labels of any chemical is crucial to safe and proper use. Read that again!
- Infrastructure: Warning – over time, excess use of vinegar on sidewalks will degrade your concrete and cause it to break down.
Chemicals are labeled with signal words based on their potential risk:
| Signal Word | Toxicity |
| DANGER -POISON | Extremely toxic compounds when consumed, inhaled, or absorbed through the skin or eyes, etc. (must have skull and crossbones symbol on label). Fatal at very low doses. |
| DANGER | Extremely toxic compounds that are corrosive and may cause irreversible skin and eye damage. |
| WARNING | Products with moderate toxicity. These products can cause moderate eye or skin irritation. |
| CAUTION | Slightly toxic; may cause slight eye or skin irritation. |
For reference – horticultural vinegar is labeled most often as “danger” due to its corrosive nature (can cause skin burns and blindness). By contrast, other more common herbicides are labeled as “warning” (i.e imazapyr and dicamba) or “caution” (i.e. glyphosate and 2, 4-D).
Salt: A Recipe for Soil Damage
As a weed killer – table salt (NaCl or Sodium Chloride) is sometimes used as part of a mixture or on its own. The way it works is through desiccation, aka dehydrating the plant. When salt encounters plant tissues, it draws moisture out of the cells. This causes wilting, browning, and ultimately death. If the impact of salt stuck only to target weeds, it would be a considerable alternative! Unfortunately, that is not the case.
Salty impacts:
Soil Structure & Flood Risk: When salt is used, it doesn’t stay at the surface for long. Instead, it dissolves with water and seeps deeper into the ground. This creates clumps of salty soil – think underground salt flats. These aggregates of soil slow or stop water flow and eventually result in localized flooding.
Soil Chemistry: While some plants tolerate salty soil, most don’t. Both sodium and chloride are plant nutrients at the proper levels, but in excess, they are fatal.
Soil Organisms: Beneficial soil microorganisms, like bacteria and fungi, and macro-organisms, like worms and insects, are vital for nutrient cycling and overall soil/plant health. High salt concentrations can be toxic to these essential lifeforms, leading to a decline in microbial activity and diversity. This disruption compromises soil health – which in our interconnected ecosystem can cause a domino effect: unhealthy soils make for sad plants, which may reduce forage for wildlife, which may reduce healthy prey for predators, and the list goes on.
Collateral Damage: Salt leaching from treated areas can harm surrounding vegetation and water sources, impacting non-target plants and aquatic ecosystems unintentionally.
Epsom Salt: A Weed Fertilizer
Honorable mention – Epsom salt is actually used as a plant fertilizer. Epsom salt, AKA magnesium sulfate, helps supply magnesium (which enhances chlorophyll production & nutrient uptake) and sulfate/sulfur (which enhances plant metabolism & protein/enzyme activity). The only way Epsom salts could be used for weed control is through overfertilization, which requires a lot of product and will impact any surrounding plant and soil life.
In conclusion: Epsom salts may be an effective fertilizer for plants you want, but are not an effective method for plants you’re hoping to get rid of.
A Comparison with Herbicides
While salt and vinegar may seem like convenient alternatives to synthetic herbicides, it’s essential to consider the broader context of these chemical weed control methods:
- Regulatory Approval: Synthetic herbicides undergo rigorous testing and evaluation before receiving regulatory approval for use. These evaluations assess potential impacts on human health, non-target organisms, and the environment, ensuring that approved herbicides meet stringent safety standards.
- Environmental Impact: Approved herbicides are designed to minimize environmental harm, with formulations and application methods tailored to target specific weeds while minimizing off-target effects. Additionally, many herbicides undergo extensive studies to assess their impacts on soil health, biodiversity, and ecosystem function.
- Human Safety: Approved herbicides are subject to strict safety regulations to protect human health during application and subsequent exposure. Proper handling procedures and protective equipment requirements help mitigate potential risks to applicators and bystanders.
Herbicides are not appropriate for all weeds and all settings, so they should be used with careful consideration of impacts. They are one tool among many to manage noxious weeds. This post is not advocating the use of herbicides, instead we hope that readers will consider the chemical impacts of salt and vinegar before using them in a garden or natural area.
Chemical-Free Weed Control
If you were considering salt or vinegar out of a desire to avoid chemical methods, the good news is that there are a variety of non-chemical weed control options for each species depending on the situation. Other options include manual control (digging, pulling, cutting), mechanical control (mowing and burning), cultural control (tarping and mulching), and more.
If your weed of concern is a listed weed on our list, you can find it on our website! We have a webpage written for almost every listed species that has more information, including control options: kingcounty.gov/weeds
For all other species, we recommend reaching out to Garden Hotline with photos and specifics of your situation: gardenhotline.org/question
Conclusion
Remember, a healthy ecosystem starts with healthy soil. Use alternatives that support the environment rather than compromise it. By approaching weed control with a focus on sustainability and soil health, we can create thriving gardens and ecosystems that are resilient and productive for years to come.
References/more reading:
Can I use vinegar to control weeds? (orst.edu)
Effects of salinity on the soil microbial community and soil fertility – ScienceDirect
Economics of salt-induced land degradation and restoration (hal.science)
Vinegar: An Alternative to Glyphosate? | University of Maryland Extension (umd.edu)
Why It Can Be Dangerous to Use Vinegar to Kill Weeds (goodhousekeeping.com)
Garden Myth: Salt Makes a Good Weed Killer – Laidback Gardener
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