If you enjoy visiting social media sites like Pinterest or Facebook, you’ve seen posts touting “natural” weed killer recipes involving one pantry staple or another. In a quick search, I’ve found recommendations for salt, vinegar, baking soda, and cornmeal, as well as recipes combining some of these ingredients. Do any of these work? Does “natural” equal safe for the environment? Let’s take a look.
Vinegar seems to be a miracle product, if you believe the internet hype. There are many recipes for homemade weed killers containing vinegar – full strength, diluted, with or without soap, salt, and/or additional ingredients. Vinegar itself contains acetic acid, generally at a concentration of 5%. Acetic acid kills by desiccating any foliage it contacts – weeds as well as other plants. It does not kill the roots of plants, so regrowth will occur unless plants are very young. Some plants, such as those with waxy or hairy leaves, do not absorb as readily as others, so vinegar may be less effective on these plants. Bottom line – vinegar will burn the leaves it touches, including those of your lawn and landscape plants. Control is short-term, so you’ll have to apply repeatedly.
Sprinkling or spraying salt on a plant will kill the leaves the salt touches by drawing water out of the plant, eventually causing it to dry out. Like vinegar, salt only damages what it touches, leaving the roots of weeds intact and ready to re-grow. If you want to kill a weed or two in the cracks of your sidewalk, salt could be effective, but keep in mind that salt dissolves easily in water and can be carried to other (desirable) plants in your lawn. A high salt concentration in the soil can impact growth of anything planted in the treated area after the application as well. Plants’ uptake of water from soil can be impacted as can the availability of nutrients in soil Think about the types of plants that grow near the ocean – they have adapted to a high salt concentration. Most of the popular landscape plants and food crops grown in the Triangle do not have this adaptation and will not thrive in salty soils. We’ve all heard the legend of the ancient Romans “salting the earth” of those they had conquered – even if it isn’t true, should we really salt our own bit of earth?
In the 1990s, scientists at Iowa State University found that corn meal gluten (NOT the corn meal found in our pantries, but a high nitrogen by-product of milling) reduced seed germination in studies. The corn meal gluten was not specific – it inhibited germination of some – not all – weeds and some desirable plants. In addition, it didn’t kill existing weeds – in some cases the nitrogen acted as a fertilizer to existing weeds. Field trials of corn meal gluten have had mixed results, and the cost is higher than other weed control methods. It certainly doesn’t seem to be a household miracle either.
One website I saw touting baking soda as a weed killer claimed that “baking soda neutralizes the pH of soil and nothing can grow there”. Another claimed that “sodium bicarbonate is deadly to weeds”. First, the pH claim is ridiculous. Most plants grow best in slightly acid to neutral soil (pH 6.0 – 7.0). Our NC soils tend to be more acidic than this, so adding baking soda could conceivably raise the pH to a more beneficial level, not to a toxic level. Garden lime is a more effective way to raise the soil pH than baking soda. As far as being deadly to weeds – I would speculate that it works in a similar fashion to the previously mentioned home remedies – by desiccating foliage but not killing roots.
To summarize: while any of these remedies might provide some temporary weed control, your best natural, organic weed killer would have to be your own two hands. I’m afraid there’s just no substitute for old fashioned hard work if you would prefer not to use chemical weed killers.
In addition, please keep in mind that just because something is natural does NOT mean that it is harmless. Some of the world’s most deadly poisons are naturally occurring substances. Others can have unintended consequences (such as damaging desirable plants in the quest to kill weeds). Before you try a home remedy, check with a research-based source to determine that remedy’s safety and effectiveness.