Home remedies abound in the horticultural world. Some gardeners swear by their mixtures of a little bit of this, and a little bit of that, but Extension does not readily recommend the use of homemade pesticides. Perhaps your anti-Japanese beetle potion warded off the critters last year. But what if you get the amount of the ingredients out of balance next time or what is happening in the long term to your plants, soil and environment? An example which was recently brought to my attention by a McDonough County Master Gardener is the use of salts and vinegars for weed control. These two substances are common ingredients in many purported weed remedies found on the internet. Contrary to some beliefs that the internet never lies, just remember that any Joe Shmoe (or Jane Shmoe for that matter) can post something on the World Wide Web.
Vinegar is reported to be an old-world herbicide, used for generations. Plus, vinegar is sold commercially as an herbicide treatment. Now let's distinguish kitchen vinegar and vinegar-based herbicides. Dosing dandelions or purslane with vinegar from your kitchen cabinet means all you're missing is some olive oil for a nice salad. Simply put, kitchen vinegar does not make a good herbicide. The concentration of acetic acid, a compound found in kitchen vinegar, is typically around 5%. A concentration that low is just not strong enough to kill any but the smallest of weed seedlings.
Higher concentrations of acetic acid are marketed commercially in vinegar herbicide formulations. Often these are billed as organic options to conventional chemical herbicides. Vinegar herbicides are effective against young seedlings and annuals somewhat. But acetic acid does not translocate to other plant parts, therefore any perennial weed or weed with a well-established root system can regrow. Additionally, the contact kill delivered by the vinegar herbicide affects soil microbes and soil pH, though studies show these effects are often minimal and short-lived. Yet, some effects can be long-term for the occasional unlucky amphibian I read about in this e-Extension blog post about using vinegar herbicides.
So just how much acetic acid is required to be effective? According to Michelle Wiesbrook, University of Illinois Pesticide Safety educator, studies indicate that acetic acid concentrations of 10 to 20% provide effective weed control in the range of 80 to 100%. Homeowners should note that concentrations of acetic acid this high are incredibly harmful to humans. Any contact with the skin and eyes causes' irreversible corrosion and damage, meaning gloves and goggles or a face shield are a must when using vinegar herbicides. Just because a product is labeled as 'Organic' does not mean it is harmless, but that's another article.
Salt is another common ingredient found in homemade weed killers and has been used for centuries. If we crack open our history books we will read that a key weapon used by ancient armies was salting the fields of their enemies. Sure salt does the trick in knocking down weeds, but what are the long-term effects? To this day some gardeners still salt asparagus beds, which was once a recommendation given by Extension. It seems to be an effective strategy, yet as the salt levels in soil rise above the tolerance of the asparagus- the decline of your favorite perennial vegetable is imminent. Salt is soluble and thus highly mobile in your soil allowing it to spread to areas planted with desirable vegetables and ornamentals, damaging them along with your weeds.
One remedy to high salt levels in your garden bed is to leach the material out of the top layer of soil with repeated soakings of water. Luckily, like vinegar, the effects of using salt in the landscape are not long-term and can be remediated.
It is always best to leave the homemade concoctions where you found them on the internet and opt for commercially available products which have been tested and registered with the EPA. The testing required by the EPA determines both the benefits and adverse effects of pesticides. And of course always follow label directions. Pesticide labels are there to ensure the proper use of the product which protects you and the environment. If you have questions about what pesticide is well-suited to your situation, feel free to contact your local Extension office.
Want More Information? Check out my references for more information on home horticultural remedies.
Take a look at Michelle Wiesbrook's HYG article Registered Herbicides Recommended Over Non-Conventional Weed Killing Mixes Touted Online. In this article Michelle dives into the use of vinegar, salt and more!
Sandy Mason, horticulture educator, writes about the use of vinegar as an herbicide. Vinegar - Salad dressing or weed killer?
At the Monmouth Research Farm- Kyle Cecil, small farms/local foods educator, is investigating no-till, chemical free weed control. Click the link to watch the news story Alternative Weed Control.