In recent years, there has been increasing skepticism toward traditional weed killers like Roundup. The skepticism seems to be focused on whether or not the chemicals in these products are really safe for the environment.
This has led many gardeners to look for alternatives to traditional herbicides, including one vinegar-based herbicide that has gone viral on social media multiple times. So the big question is, do these “natural” weed killers actually work?
Homemade, “natural” weed killers do not work in the long run, can decrease the quality of your soil, and pose safety risks to gardeners. However, there are brands of organic herbicides that have proven effective at controlling weeds and are much safer alternatives to “natural” weed killers.
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First, let’s clear up some confusion about the terms “chemical,” “natural,” and “organic.”
“Chemical” vs. “Natural” vs. “Organic”
Chemical Weed Killers
When people label something as “chemical,” they often mean “harmful.” This is a highly misleading assumption.
Chemicals and chemical compounds are literally everywhere: in the food we eat, the cleaning products we use, and even the air we breathe. Water itself is a chemical compound consisting of two hydrogen atoms combined with one oxygen atom.
In terms of weed killers, the term “chemical” has come to refer to traditional herbicides that rely on synthetic chemicals to control weeds. “Synthetic” simply means “man-made” or “produced in a lab but not found in nature.”
Throughout this article, I will refer to traditional herbicides, like Roundup, as “synthetic” to avoid confusion, since all weed killers rely on chemical reactions to get the job done.
Natural Weed Killers
The word “natural” means “naturally occurring” or “found in nature.” In other words, a “natural” product is one that comes from the earth with no added chemicals.
The problem with this label is that people tend to label products as “natural” if they can be made with typical household ingredients. Household ingredients like dish soap, however, are not naturally occurring. They may be safe to use, but did not grow and develop in nature.
Furthermore, people often assume that if something is “natural,” then it’s free of chemicals. The problem with this assumption is that everything contains chemicals, even things that come straight out of the soil. Again, water is a perfect example, as is the glucose contained in the leaves of a plant.
For these reasons, throughout this article, I will use the term “homemade” to refer to mixtures made from household ingredients and “natural” only to refer to substances that can be found in nature.
Organic Weed Killers
“Organic” is another term that is potentially problematic. In popular usage, “organic” refers to substances that are made without synthetic chemicals.
In its most basic form, however, “organic” simply means “containing carbon.” This is why some products are labeled “organic” when they are actually chock-full of synthetic chemicals. As long as a product contains some form of carbon, technically, it’s organic.
Organic weed killers, without synthetic chemicals, do exist and have proven effective in the right circumstances. However, because the label can be misapplied, it’s important to do some research before you buy.
Throughout this article, I will use the term “organic” to refer to weed killers that don’t contain synthetic chemicals.
Homemade Weed Killers
There are several different recipes for homemade weed killers circulating on the internet. The most popular one, a mixture of vinegar, salt, and dish soap, has provoked heated responses from horticulturalists and botanists.
The idea behind this recipe is that gardeners can spray this mixture on weeds, and the weeds will be gone within hours. This concoction is described as “miraculous,” but if we break down the individual ingredients, we’ll see the reality is much more complicated.
Vinegar is acetic acid and works by burning whichever plant parts it touches. It’s a common ingredient in organic herbicides that you can buy from your local garden center, but there are several problems with its usage in this homemade weed killer.
- The kind of vinegar that you stock in your pantry is 5% acetic acid. If your weeds have passed the seedling stage, 5% acetic acid will not be strong enough to kill them because it will simply burn the upper portion of the weeds. The roots will remain intact, and the weeds will likely regrow.
- Horticultural-grade vinegar is 20% acetic acid and carries a warning label because it’s extremely dangerous to handle (source). Any vinegar that contains more than 10% acetic acid is strong enough to burn your skin or permanently damage your eyes (source).
- Vinegar will harm any plant it touches, not just the weeds you want to kill.
- When vinegar seeps into the soil, it has the potential to kill earthworms, helpful microbes, and other things that actually benefit your soil and your plants (source).
Some versions of the vinegar-salt-Dawn recipe call for Epsom salts (magnesium sulfate); some call for table salt (sodium chloride). Many people use Epsom salts and table salt interchangeably even though they’re completely different chemical compounds.
The truth is, you don’t want to use either one of these in a weed killer.
- The two main elements in Epsom salts are magnesium and sulfur, which are both highly beneficial plant nutrients. Gardeners have used Epsom salts for years as a fertilizer substitute, so it simply doesn’t make sense to include them in a mixture meant to kill plants.
- Table salt, sodium chloride, will kill plants (except those which are salt-tolerant), but salt does more than that. It destroys the soil so that plants, weeds, or otherwise, won’t grow there in the future. Furthermore, salt alters the structure of the soil so that water won’t drain properly (source).
Whether you use Dawn or any other brand of dish soap, this ingredient serves one purpose in a weed killer: it’s a surfactant. This means that it helps the vinegar and salt stick to the leaves and stems of the targeted plants.
Surprisingly, dish soap is the only ingredient in this recipe that isn’t natural, but it’s the one that is the least likely to have any affect on your plants. It will burn leaves in the heat but won’t cause any lasting harm in small quantities (source).
Other Common Ingredients
- Bleach and Borax are included in some homemade weed killers, but like dish soap, these are not actually natural ingredients. Furthermore, they can harm children and pets, and they can damage your soil the same way salt does, resulting in patches where plants simply can’t grow.
- Boiling water is also common. However, like vinegar, boiling water is only likely to kill the upper portion of the weed, but leave the roots intact. Furthermore, carrying pots or kettles of boiling water poses a burn risk to the gardener (source).
It’s easy to see why homemade weed killers are so appealing to gardeners. The ingredients are cheap and many of us already have them on hand. However, as attractive as it may seem to make your own weed killer with “safe” household ingredients, it is simply not a good, long-term solution for your yard or garden.
Organic Weed Killers
If you want to avoid using traditional, synthetic herbicides, but also want to avoid some of the harmful effects of using a homemade concoction, an organic weed killer may be right for you.
Organic Herbicide Benefits
- Organic weed killers, when applied responsibly, are often safer to use where your children or pets may play. This is because organic herbicides break down more quickly than synthetic ones. You should still keep children and animals at a safe distance during application, but organic herbicides don’t pose a chronic risk to their health and safety (source).
- Organic herbicides truly are naturally sourced. Many organic weed killers rely on the use of essential oils, including cinnamon oil, citrus oil (d-limonene), clove oil or clove leaf oil, and lemongrass oil. They may also contain acetic acid in the form of horticulture-grade vinegar, citric acid, or both (source).
There are several brands of organic weed killers widely available commercially. One highly regarded product is Weed Zap® (link to Amazon), a biodegradable, non-selective herbicide
Organic Herbicide Drawbacks
- Like pure vinegar, organic herbicides do not target weeds alone and will harm grass, flowers, or any other desired plant they touch.
- Organic weed killers don’t completely prevent the future growth of weeds. If you spray the weeds early on, you can decrease the chance that they’ll return.
Organic herbicides work best with other types of weed control (e.g., hoeing and mulching). If you want a once-and-for-all solution, organic herbicides are not your answer.
Applying Organic Herbicides
- Make sure to read and follow all safety instructions listed on the product! Just because something is natural or organic doesn’t mean it is risk-free.
- Spray weeds when they are less than four inches high or have developed only 2-4 leaves.
- Spray thoroughly!
- Plan to apply your weed killer more than once, especially if your weeds are more than a few weeks old.
When you see a recipe for a “natural” weed killer that you can whip up right in your own kitchen, don’t believe the claims! The ingredients may be perfectly safe in your kitchen, but can do a great deal of harm in your garden.
If you want to avoid synthetic weed killers, consult an Extension agent or horticulturist to see if organic weed killers might be right for you.