Why You Shouldn’t Use Homemade Weed killers
Making sense of internet myths
By Hannah Miller at DIY Gardening
Hello, my name is Hannah Miller, and I’m the co-owner and contributor here at DIY Gardening.
On this page, I will try and convince you not to use the homemade weed killers that organic gurus and health websites are promoting all over the internet.
I’m seeing more and more website authors, YouTube presenters and social media influencers promoting “safe” alternatives to chemical weed killers.
I’ve looked into these concoctions, and for the most part, I believe they do more harm than good.
Keep reading, and I’ll explain why they’re so harmful and I’ll suggest alternatives.
One Word: Salt
Nearly every homemade weed killer recipe I’ve seen contains salt and often in huge quantities.
Salt with baking soda.
Salt with vinegar.
Salt with washing up liquid.
Salt with cooking oil.
Salt with all of the above.
Here’s the problem; salt doesn’t degrade, and it can contaminate the soil.
Salt isn’t just toxic to weeds; it’s toxic to all plants.
The only way to get rid of excess salt in the soil is to wash it away with water.
It can take up to two years for rainwater to wash away the salt from contaminated soil, and in that time, very little will thrive in the soil.
But is Salt an Effective Homemade Weedkiller?
Studies have shown that salt is effective at browning and killing off the leaves of most weeds.
It can also completely kill off new weed seedlings.
Unfortunately, it doesn’t kill off the roots of established weeds which can start to grow back in a matter of weeks.
To kill off the roots and the entire weed, you would need to contaminate the soil with so much salt that nothing would grow there for years.
While salt is effective, it doesn’t sound very organic or safe to me; I guess that depends on what you consider organic or safe to mean.
I see salt as a non-selective, toxic metal that only kills because it’s so harmful to the soil.
As salt never degrades, it eventually gets washed into streams and rivers, where it causes more harm.
I don’t think gardeners should be using salt in their homemade weed killer recipes, and if they do, they should only use it once per year and make sure they only use enough to wet the weeds and not soak the entire area.
Vinegar – Maybe
Vinegar also browns off the leaves of many weeds and can completely kill seedlings.
Unfortunately, it rarely kills the roots and studies have shown that soon after rainfall, the weeds start to grow back.
Vinegar is a contact herbicide; it kills the green leaves and green stems of what it comes into contact with but doesn’t kill the roots.
Vinegar is quickly washed away in the soil and doesn’t hang around as long as salt does.
Vinegar is far safer to use than salt, but it’s also less effective and would need to be applied frequently, which isn’t practical for most gardeners.
Baking Soda – Nope
When mixed with vinegar, baking soda fizzes, but this is just the acid from the vinegar cancelling out the alkaline from the soda; it doesn’t produce any extra weed killing benefits.
Baking soda does contain sodium (salt) but is no more effective at killing weeds than table salt, although it’s more expensive.
The bottom line: baking soda isn’t good at killing weeds, you may as well just use salt, which I don’t recommend either.
Washing Up Liquid – Pointless
This is another fad that’s doing the internet rounds – washing up liquid.
The idea is that the oil in the liquid helps the salt bind to the leaves of weeds, making it more potent.
I’ve seen a few gurus recommend other oils but they all achieve the same results.
Unfortunately, we are back to square one as salt is bad for the soil (and rivers, streams etc.), so it doesn’t matter if it’s mixed with washing up liquid or not; once the liquid degrades, the salt will remain and persist.
Salt is not a good homemade weed killer because it’s toxic to the soil.
Alternatives to Homemade Weed Killers
I personally don’t use any homemade weed killers in my garden.
I would never use salt but would consider vinegar if I was desperate; at least it doesn’t persist.
There are several alternatives and below are my recommendations:
1) Electric Weed Killers:
I’ve tested an electric weed killer before, and it worked really well; the key is to give the weed a 5-second blast and then move on, the leaves will die instantly, but the green matter may hang around for a few days.
There’s no need to blast the weeds to a crisp; this is a common mistake and just burns out the heating element in the tool.
I recommend electric weed burners for all weeds on hard surfaces; you can ditch the nasty chemicals, there’s no salt toxicity, and they’re cheap.
Weeds produce seeds that spread to other parts of the garden by the wind, rainwater, or a gardener using a hosepipe or watering can.
The seeds then germinate and produce more weeds.
One way to break this cycle is to use mulch in your borders.
A 10-15cm thick layer of bark or mulching compost will stop light from penetrating the soil; without this light, the seeds can’t germinate.
Mulching is a proven and accepted method of suppressing weeds in borders, and no chemicals are needed either.
It also stops water from splashing around the plants when the gardener uses a hosepipe – a common way pathogens and pests spread from one plant to another.
3) Try This Lawn Weed Removal Tool:
Lawn weeds are difficult to get rid of without resorting to harsh chemicals and none of the homemade weed killer recipes I saw online was suitable for weeds in lawns.
Have a look at the product in the photo below.
This weed extractor tool pulls up weeds and up to 10cm of roots too.
No chemicals, salt or vinegar required.
To date, this weed remover has 9400 customer reviews on Amazon.
76% of the reviewers gave it a 5-star rating.
13% gave it a 4-star rating.
Looking deeper into the reviews, I found that most of the lower ratings were due to postage issues, delays and transit damage etc.
The customer feedback for this weed removal tool speaks volumes.
4) Use Pelargonic Acid:
Pelargonic is a natural, organic fatty acid that’s been used in the food industry for decades.
It can be found in many organic commercial weed killers such as Roundup Natural and Neudorff “Glycosylate Free”.
You shouldn’t use Pelargonic acid on hard surfaces as the product needs to enter the soil to degrade.
Use this natural weed killer around plants, trees, on gravel and along fences.
I recommend Roundup Natural as it doesn’t contain any other active ingredients.
Neudorff, has a similar product that will be more effective but it also contains Maleic Acid Hydrazide, which can be harmful to dogs.
You can safely use pelargonic acid under trees and established shrubs, it won’t harm them and isn’t absorbed through brown wood and bark.
Of all the commercial weed killers out there, I feel Roundup Natural are the safest.
Homemade Weed Killers – A Summary
More and more gardeners are moving away from harsh chemicals, and that’s great for the environment, but homemade weed killers can be just as harmful.
Just because a product is made from products found in the home doesn’t mean it’s safe or suitable for garden use.
In fact, many of these concoctions only work because they toxify the soil.
There are plenty of ways to kill, prevent and suppress weeds naturally; gardeners have done this for centuries, long before chemical-laden products came along.
More From Hannah Miller:
This warning about homemade weed killers was created by Hannah Miller and was posted to our blog on the 24th of June, 2021.
Hannah is a keen amateur gardener, mother and a former NHS administrator.
She enjoys gardening as much as she cares about the environment and likes to share her knowledge with others.