Wednesday, March 14, 2012

Vinegar as a Weed Killer?

The focus of this blog is not to debate organic versus man-made weed killers but to possibly enlighten you on just exactly what vinegar can and cannot do. I have used vinegar as a non-selective weed control method (and still use it today) but it does have its' limitations.

After over 30 years in the pesticide business, I have seen a lot of changes happen and used theories that do and do not work, and made use of a lot of home brew, organic pesticides and weed killers. I still use some to this day and have discarded others. I have absolutely nothing against organic methods of gardening or farming and I have been using those methods for the last twenty years, long before it became fashionable.

The lack of weed control options has and will continue to be very frustrating for organic farmers, gardeners and homeowners who do not want to use synthetic pesticides. The idea of using household vinegar as a herbicide is very appealing, it's natural, inexpensive and readily available.

How Vinegar Works as a Weed Killer

The acetic acid in vinegar is the active ingredient. When applied to plant foliage, the acetic acid destroys cell membranes causing plant tissues to dry out. Acetic acid does not translocate (move through the plant and into the root system) so only the foliage of treated weeds are killed, not the roots. Re-treatment will be necessary.

Vinegar-based herbicides are contact and non-selective, which means any plant foliage that is sprayed will be damaged. So, be very careful that you only apply to your target weed or grass, any surrounding plants will be damaged. Consider adding vegetable oil in your mix. It serves as a drift control agent.

Tips for best results: Apply vinegar on hot, sunny days. It works best on young (less than 3 weeks old) and rapidly growing weeds.

Why Homemade Weed Killers Are Sometimes Not a Great Idea

Yes, vinegar is an environmentally friendly, natural weed control option, but mixing up a home brew of vinegar weed killer may not the best idea.

  • The higher the concentration of acetic acid, the better it will work. Kitchen grade vinegar is only 5% acetic acid and is not a very good weed killer. Horticultural vinegar is much stronger -- 15 to 20% acetic acid -- and a much more effective herbicide.
  • "Yeah, but I have a recipe that includes salt, dish soap and citric acid". Oh, my. Never use salt unless you want nothing else to grow! The only additive that will increase weed control is dish soap. Dish soap will help the mixture penetrate the target weed, especially through a waxy coated leaf, such as dandelion. Other additives are just a waste of time and money and do not increase weed control. The percentage of acetic acid and volume applied to weeds determined effectiveness.
  • WARNING: Handle with care! The acetic acid in vinegar is an acid and acid is corrosive. Any acetic solution above 5% must be handled with care, it can burn skin and cause eye damage.
  • Weed Pharm is a vinegar weed killer that is labeled for organic use.
Although not organic, glyphosate (Roundup) is a more suitable and safer choice for non-selective weed control. Contrary to popular belief, it is safe to handle and is bio-degradable, when used according to the label directions and will kill grasses and weeds to their roots. Re-treatment is normally not necessary.
  • Horticultural vinegar products carry the Danger signal word on the label, while Caution is found on glyphosate. 20% acetic acid is not something I want to handle, glyphosate is much safer for the applicator.
  • A single application of horticultural vinegar will kill many annual weeds but perennial weeds need to be retreated frequently. A single application of glyphosate will eliminate most weeds, killing them down to the roots.
  • When used according to the label, glyphosate will not harm the soil or pollute water supplies. It cannot leach into and contaminate ground waters because it forms a strong chemical bond with soil particles where it quickly breaks down into harmless elements.
Organic gardening is a very noble pursuit and I'm very much in favor of reducing or even eliminating chemical usage. Vinegar weed killer home brews made from food grade products are not very effective. Glyphosate is safer to handle than horticultural vinegar and a much more efficient herbicide. If used according to the label, glyphosate is safe to use around homes and will not harm the environment.


Sherwood Botsford said...

Good post on the use of vinegar.

My problem with glyphosate is that it is too effective. I always end up killing something I didn't intend to.

Glyphosate is not permitted for use in potted woody ornamentals. Seems that the breakdown products don't disperse well in a pot.

In passing: Vinegar is expensive if you are doing lots of weed control. Is it just the fact that's acidic? If you are going to use an acid, would dilute muriatic acid work as well?

The plant whisperer said...

Yes, it is expensive if you purchase the "Grocery Store" vinegar (doesn't work as well (different formulations). Instead, you will want to buy formulations made specifically for weed control applications which you can purchase at local farm stores. Muriatic acid will work, too but be careful using it.