I once had a hairdresser use a “natural” hair color product on my hair. Within a day or so, I developed a rash at my hairline that was uncomfortable enough that I had to see a dermatologist. When I defended the stylist’s choice as “natural,” the doctor noted, “So is poison ivy.”
All this to say that just because something is “organic” doesn’t mean it can’t have detrimental effects.
Many gardeners are choosing organic weed killers (herbicides) in an effort to protect pollinators, other beneficial insects, and earthworms, as well as to protect soil health. And this is certainly a reasonable goal. But how risky the product is depends on the active ingredients, concentration, where and how it is applied, and what can potentially be exposed at that time.
So let’s take a look at a few of the more common organic herbicides in use today and any precautions we should take when using them.
First, What Counts as an Organic or Naturally Derived Weed Killer?
For a home gardener, the products you are most likely to see contain ingredients such as:
- Acetic acid, the active acid in vinegar
- Citric acid
- Clove oil or eugenol
- Cinnamon, thyme, mint, orange, or other plant-derived oils
- Fatty acids or fatty-acid soaps, including pelargonic/nonanoic-type ingredients
- Combinations of acids, oils, and surfactants
How They Work
Most of these naturally derived products are nonselective contact herbicides.
That gives us two important words to explain.
Contact means they primarily damage the foliage they actually touch. Acids and plant oils burn the leaf surface. This causes the foliage to dry out quickly. They generally don't travel through the plant to kill extensive roots and rhizomes the way a systemic herbicide can.
Nonselective means they can injure all plants, including desirable ones. They don’t know the difference between a weed and your favorite flowering annual that might be growing beside it.
So you’ll need to be very cautious when applying these products so that you don’t accidentally kill plants you want to keep.
General Precautions for Home Gardeners
1. Always Read the Product Label
“Natural” doesn't mean you can skip reading directions. Remember my hair color story.
Products containing similar ingredients can have very different concentrations. Household vinegar is typically around 5% acetic acid, while horticultural herbicidal vinegar may contain about 20%. Horticultural vinegar carries a DANGER label because of acute exposure risks.
Always use the product at the labeled concentration. Don’t assume adding more makes it a better or safer weed killer.
2. Protect Your Eyes and Skin
This is particularly important with acid-based products.
Use appropriate eye protection, long sleeves and pants, waterproof gloves, shoes and socks, and other label-required protection. Some organic herbicides are concentrated enough to burn skin or seriously injure eyes. Follow the label’s protective-equipment instructions just as you would with any other chemical.
3. Remember That They Are Nonselective
Don’t broadly spray weeds growing among desirable flowers or vegetables.
A weed growing in a sidewalk crack is a much easier target than one growing in the middle of your perennial border.
4. Young Weeds Are Usually Much Easier to Control
These products tend to perform best on small annual seedlings as opposed to established plants with bigger root systems. Since many of these products work by burning or killing the leaves of the plant, this doesn’t necessarily mean that the roots will be killed as well.
If you need to spray again, this doesn’t mean you need a stronger product. It just means you may need a different method to get rid of that weed.
5. Don't Assume “Organic” Means Certified, Risk-Free, or Environmentally Neutral
Products described as natural, organically derived, or even approved for some organic uses can still be concentrated herbicides. Judge them by the active ingredients, label directions, and how you plan to use them, not by the word “natural” on the front of the bottle. And as we said before, always follow the directions.
For more information on using vinegar, and vinegar combined with other household products, as a weed killer, please see our article:
Is Vinegar Really a Good Natural Weed Killer?
What About Earthworms and Beneficial Insects?
If you’re choosing an organic weed killer because you’re concerned about earthworms and beneficial insects, I do have some good news.
There really isn’t strong evidence that careful, targeted use of most organic herbicides routinely destroys earthworm or beneficial-insect populations.
But that doesn’t mean there's no risk.
Some ingredients used in organic weed killers can affect insects when those insects are directly exposed. The effect depends on the chemical and the type of insect.
Earthworms are affected by the conditions in the soil around them. Heavy or repeated applications of acidic products like vinegar can temporarily change soil conditions and microbial activity, although these effects are generally short-lived.
The practical lesson is fairly simple:
- Spot-treat weeds rather than spraying large areas.
- Keep the product on the weed foliage as much as possible.
- Avoid repeatedly soaking the soil.
- Don’t spray flowering weeds while bees or other beneficial insects are actively visiting them.
- Follow the product label, even if the ingredients sound familiar or natural.
A weed growing in a driveway crack is one thing. A flowering weed covered in bees in the middle of a garden bed is another. Wait until the flowers die and the bees move on to another plant before treating the weeds.
Prevention Is Still the Best Weed Control
If your goal is to protect earthworms, pollinators, soil microbes, and the plants you want to keep, the safest weed killer may be the one you don’t need to use.
That means preventing weeds whenever you can.
A few simple practices can dramatically reduce how many weeds you have to deal with:
- Cover bare soil with mulch.
- Plant groundcovers or other plants closely enough to shade the soil as they mature.
- Pull or hoe weeds while they’re still small.
- Avoid unnecessarily disturbing soil, which can bring buried weed seeds to the surface.
- Remove weeds before they flower and set seed.
Mulch is especially useful because it does more than suppress weeds. It helps conserve moisture, moderates soil temperature, and creates a better environment for many soil organisms.
And from a practical standpoint, preventing ten weeds from germinating is a lot easier than figuring out how to kill ten mature weeds later.
The Bottom Line
Organic weed killers can be useful tools, but “organic” or “natural” doesn't automatically mean harmless. Handle these products carefully and apply them minimally.
And if protecting beneficial insects and soil life is important to you, start with prevention, remove weeds while they’re small, and use weed killers only where they truly make the job easier.
The goal doesn’t have to be a perfectly weed-free garden. It’s a garden you and your insect friends can enjoy without creating more work for yourself.
