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The Parklands

Using Organic Herbicides in the Garden

Getting rid of weeds can be a real hassle. When the garden or lawn starts getting out of control, it is common to run to the nearest garden center and pick up the first herbicide on the shelf that will kill every kind of weed in your landscape. It may seem like the quickest and easiest solution to your unwanted plant issues, but there are a few alternatives that are safer to use and easier on the environment.

As gardeners for The Parklands, we must always be aware of our surroundings, asking ourselves a couple of questions before applying any type of herbicide:

  • Who is going to come into contact with the areas I am treating?
  • How is the application going to affect the wildlife, land and water around me?

Many of the most popular herbicides are toxic to humans or other critters. For example, the extreme decline we are seeing in bee population is partly due to the use of neonicotinoid pesticides. Synthetic pesticides can take a long time to break down and disappear from the environment. If used too frequently, weeds can even develop a resistance to a chemical to the point where it will no longer be effective in killing the plant.

The most important thing to remember is to always read the label before you use a pesticide and to do the research on it. Take time to read studies on the effects the pesticide can have on animals and the environment. Find out who funded the study if you can, to make sure you aren’t reading a biased opinion.

These concerns have motivated our gardening team to experiment with the use of organic herbicides. Our current favorite is a mix of undiluted extra-strength vinegar (20% as opposed to the normal 3-5% that you find in the grocery) and about a teaspoon of liquid dish soap per gallon of vinegar. The vinegar kills the plant while the soap increases its effectiveness by acting as a surfactant. *If you are spraying an area where you don’t want plants to grow in for a while, you can add a cup or two of salt to the mix. We do this in areas like our gravel paths or in the cracks of sidewalks. You have to be very careful when using this method though, because repeated use of salt will prevent anything from growing in the treated area for a very long time.

Other organic herbicides include corn gluten meal, which can be applied as pre-emergence weed control (may prevent seeds from germinating), clove oil and other essential oils, citric acid, and ammonium nonanoate (an herbicidal soap). These are all non-selective, meaning they will kill any plant they come in contact with. The only selective organic herbicide I know of is chelated iron, which should only kill broadleaf plants like dandelions and thistles, but not grasses.

Although organic herbicides sometimes offer a less toxic alternative to synthetic herbicides, this isn’t always the case, and organic doesn’t always mean safe. Extra-strength vinegar can cause burns to your skin or severe damage to the eyes. Certain essential oils can cause skin irritation. It is always a good idea to use caution whether the pesticide you are using is organic or not. I recommend wearing eye protection and gloves while you are mixing the chemical and gloves when you apply it.

Another drawback to organic herbicides is they tend to require repeated applications. Most are not systemic, so they don’t move through the plant and affect the roots as well. Annual weeds can be killed with one treatment, but perennial weeds will probably re-sprout. Repeated applications will weaken and can eventually get rid of them. As I said before, most organic herbicides are non-selective so be careful not to spray any plants that you want to keep around. They can also be more expensive than synthetic herbicides and are probably not reasonable to use on a large scale.

One important way to deal with weeds is just that—learn to deal with them. Our culture has conditioned us to believe that our landscape needs to be absolutely weed-free at all times. Constant use of pesticides no doubt has a negative effect on both our health and the environment. If you feel like you need to get rid of a weed, the simplest, quickest and most effective way is always to just bend down and pull it. I recommend experimenting with alternatives to popular synthetic pesticides, but remember to always use caution and be aware of your surroundings, even if your herbicide is organic.

Matt Jenne was born and raised in Louisville, KY. He attended Eastern Kentucky University and graduated with a Bachelors Degree in Horticulture in 2012. While he was in school, he worked for Louisville Metro Parks as a member of the Landscape Division. Matt started as a Park Attendant for the Parklands in early 2013 and was promoted to Zone Gardener shortly afterwards. He currently manages the plantings in the Humana Grand Allee, and also runs his own landscape business on the side. In his free time, Matt enjoys hiking, camping and gardening.