Lawn care myth: Vinegar is an effective weedkiller

I have recently been contributing to a discussion on the great Gardeners Corner Forums on the merits of using vinegar as a weedkiller.

This is something that I have heard about before and a quick Google search reveals a number of blogs, websites and resources claiming that acetic acid (more commonly, vinegar) is a perfectly safe and effective herbicide for all garden weeds.

The truth to this is, it is both right and wrong!

Vinegar as a weedkiller – The facts:

Myth 1: Household vinegar is an effective weedkiller

It is true that vinegar does kill green vegetation on plants that it comes into contact with and that it is even sold as an ingredient in some specialist herbicides in the US. However, acetic acid is only ever effective as a contact herbicide, killing only parts of the weed that it comes directly into contact with.

Any parts of the plant which it does not touch directly remain completely unaffected. This will include any leaves not touched, the root and any growth nodes from which new leaves can form. This means that it is only effective on small annual weeds, which often easily just pulled out by hand. The majority of garden weeds such as dandelions, are extremely tough. Just killing a few of their leaves will pose no threat to them. They simply send up new leaves quickly and bounce back to full strength in a matter of days.

This means that household vinegar cannot really be compared to weedkillers that have been designed and tested to thoroughly kill weeds, root and all.

Myth 2: Vinegar is an easy to use weedkiller

As vinegar is a chemical which only kills plant tissue, so it needs to be in direct contact with the target plant. However, it will also damage sensitive plants and like these may take a long time to recover from acid damage, far longer than a weed. Have a look at your garden or lawn and asses if you would enjoy trying to paint every single weed, avoiding every plant you want to keep. For general weed control, it’s obvious that it is not really a viable option.

Myth 3: Vinegar is totally safe

Household vinegar is only 5% acetic acid. It would work more effectively as a weedkiller at higher concentrations. But once you get above 7% it starts to become a quite a dangerous chemical to handle with a risk of skin burns, and a possible danger to fish if spilt in water. Not exactly harmless.

Myth 4: Vinegar is safe to use as a base for a “home herbicide”

Some Internet sources worryingly give out instructions of how to mix together your own herbicide at home. These give examples of using ingredients like detergent, salt and even bleach! I strongly advise against this. These chemicals are not designed for use in the garden and can end up doing much more harm than good. You don’t know what they may contain and you should only use them as labelled. In some areas use of all chemicals “off label” is illegal with heavy fines if caught. These rules are there to protect the environment. Products designed for garden use have been fully tested and licensed for that use. To use other household chemicals because you think they are better is very poor judgement.

Retails herbicides are designed to do their job as safely as possible, with as little impact to their environment as possible. If you do not wish to use any chemicals at all in your garden you are much better off getting down on your hands and knees and hand pulling weeds regularly rather than rooting round in the kitchen cupboards for home remedies.

In summary, leave the vinegar for your chips!

References:

• Oregon State University – PDF Fact Sheet for Vinegar/Acetic Acid Recommendations
• Garden myths blog – Does vinegar kill weeds?