GOLDEN VALLEY, Minn. — Here’s a hot topic to discuss this week, one that will certainly stir up some divided opinions. Here’s ours.
Many dedicated gardeners have seen the recipe online and many have used it: Vinegar mixed with a combination of dish soap and/or salt for a homemade weed killer. I’ll admit to using it.
And while these household ingredients "seem" very safe, in truth they aren’t good for your soil.
Vinegar - especially strong horticultural vinegar - is highly acidic. Horticultural vinegar is 20-30% acetic acid and is far from a safe product. Contact with skin, eyes or lungs can cause severe damage.
Vinegar works as a weed killer by burning the leaves it comes in contact with. It's important to note that it also burns the bugs, frogs and toads, bees and bugs it comes in contact with.
Salt that many people add to the solution (table salt or Epsom salt) never leaves the soil and water it pollutes. Salt pollution, mainly from road and sidewalk treatments is one of the biggest problems plaguing our waterways.
If you choose to use vinegar as an herbicide know this:
- It’s not a harmless alternative
- It only tends to be effective on very young weeds
- It’s not cheap and is a waste of money on mature, established weeds
- It also is not 100% effective and generally is not effective for grassy weeds. Large and grassy weeds may look like they have been killed initially, but they usually regrow within a week
- Vinegar does not impact the roots of the plants sprayed.
Here's two cents from the University of Maryland on using vinegar to address weeds.
Pros:
- Excellent control when contacting very small annual broadleaf weeds
- Rapid kill rate (Over 90% of treated plants should die within 24 hours).
- Acetic acid products break down quickly in the environment
- Most useful for managing weeds in gravel and on patios/sidewalks.
- These contact herbicides fit into an integrated pest management program; although weeds require monitoring for best control timing.
- Non selective, but mainly kill broadleaf weeds. Burns back grasses temporarily.
Cons:
- No residual activity. Will kill or damage any plants they touch.
- Weeds must be small (timing is important – within 2 weeks of germination)
- Roots are not killed; repeat applications are needed for larger weeds and perennial weeds
- Good spray coverage is essential (70 GPA+)
- Sharp vinegar odor may be unpleasant
- Spray equipment must be cleaned after application, particularly metal equipment. Avoid using spray equipment with metal working parts such as metal spray lines or metal nozzles.
- Spray drift may damage desirable plants.
- Do not apply to reactive metals such as aluminum, tin, iron, and items such as fencing or lawn furniture. Avoid spraying the material onto masonry sidewalks and structures. If the product contacts these surfaces, staining, mottling, etching, or other harm to the finishes or surfaces may occur.
- Do not apply more frequently than every two weeks
- Treatments must be delayed 24-48 hours or more after rain
- Severe eye irritation, burns, and possible irreversible damage potential. Vinegars with acetic acid concentrations of 11% or greater can burn the skin and cause severe eye injury, including blindness.
- Severe skin irritation and possible allergic sensitization
- Prolonged or repeated exposure may cause dermatitis, chronic bronchitis, and erosion of teeth
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