Oxalic acid, aka oxalate, is a substance found in many types of plants. This substance is generally thought to be more harmful to people than it is to plants. Oxalic acid is used as a commercial cleaner for removing stains, preparing wood for treatment, or stripping paint. Many people use it to clean decks, patios, and for power-washing the siding of their homes. In these applications, there is a much higher concentration of oxalic acid than is natural. The question remains, “Will oxalic acid kill grass in high concentrations?”
Will Oxalic Acid Kill Grass?
Oxalic acid should not kill grass in any reasonable concentration of a cleaning solution. As most cleaning solutions recommend rinsing the area well or using water in the application of oxalic acid, the risk is reduced even further.
The caveat to this is that many companies that sell oxalic acid recommend not-so-lawn-safe instructions for what to do after applying the oxalic acid. It is often recommended that all cleaned surfaces are wiped down with baking soda. They also recommend that any remaining cleaning solution have baking soda added to it.
If you choose to follow these directions, remember that the baking soda, and anything that it is added to, does have the potential to harm your lawn or kill patches of grass. Dumping these solutions on any patch of grass will likely cause browning. This may be why oxalic acid has developed a small reputation for being more harmful than it claims to be.
What Does Oxalic Acid Do to a Lawn?
Whether you happen to have runoff from a cleaning project or a bag of straight oxalic acid spilled directly on your lawn, the results should be the same- the oxalic acid itself won’t harm the grass planted there or any plants within reach. Treat all oxalic acid spills, including runoff from any household cleaning or DIY projects by diluting the acid with water.
How Do You Clean Up Oxalic Acid?
An oxalic acid spill is best cleaned up with water, any kind. Dilute any spilled oxalic acid solution or powder until it is no longer visible and there is no longer a “fizz” at the site of the spill. A slight fizzing sound may result in a slightly raised pH over time. After the spill has been cleaned up, it’s never a bad idea to check the pH in the area and adjust it as needed. Though not harmful to your lawn directly, oxalic acid is an acid and most lawns prefer a pH closer to neutral or just slightly acidic.
How Do You Neutralize Oxalic Acid?
Oxalic acid added to a lawn is best neutralized first with water and then the pH may be adjusted with a soil additive. Lime (calcium hydroxide) is the most common choice for an alkaline additive to soil or lawns and is sometimes used in industrial processes to neutralize oxalic acid.
Is Oxalic Acid Good for My Lawn?
Oxalic acid provides no lawn benefits beyond a slight acidity if you have a problem with highly alkaline soil. However, if you have ever applied a copious amount of lime to your lawn to reduce a heavy flea population, oxalic acid is one of the easiest ways to neutralize this amount of lime after it has done its job in the same way that lime can be used to neutralize oxalic acid.
However, though oxalic acid isn’t always a good lawn additive for common reasons, it is a relatively harmless and inexpensive first-line treatment for mite infestations. Varroa mites, spider mites, harvest mites, and lawn mites are all likely to have their populations heavily reduced after the application of oxalic acid to the lawn and surrounding greenery.
Related Article: What Kills Grass? The Full List
Is Oxalic Acid a Good Lawn Pesticide?
Beekeepers use oxalic acid for the management of Varroa mites. Recently, these mites have become problematic in North America and oxalic acid has been approved as an official treatment for beehives and the surrounding area to kill these mites. Oxalic acid has a kill rate of about 95% in the case of Varroa mites when applied at a rate of about 1-2 pounds per acre.
It is also proposed that a weak solution of oxalic acid and water may be sprayed on lawns and decorative plants to reduce or eliminate spider mite, lawn mite, and harvest mite populations. If used, this spray is best applied in late fall or at the beginning or end of a period of dormancy for best control.
Oxalic Acid is Generally Lawn-Safe
Does oxalic acid kill grass? No, oxalic acid is safe for nearly any type of plant and generally does not harm soil or most larger, beneficial insects and worms. This makes it a well-known, environmentally friendly cleaning agent. Further, with the new potential for it as a treatment for mites, oxalic acid may be a good thing to keep on hand.
jh says
Great article Tom.
I came across a detailed beekeeper’s article, about using OA to fight mites in hives, when searching for possible repellents for rabbits (our neighborhood has thousands). We have watched these rabbits decimate our cacti and succulents, as well as all other manner of plant…while there are lush green lawns all around us (we have xeriscaped our yard).
I’ve tried all the “bunny friendly” remedies and am about to go the air-rifle route. However, that would mean having to dispose of the critters and while I could bury them, I’d rather not have to have a mass grave to tend.
After reading the Bee article, I wondered if applying OA would be harmful to the plants and then your article gave me some hope. I may try applying a mixture to a few test plants and see if the bitter taste deters the rabbits.
Thanks for the article, it was a missing puzzle piece, that will allow me to move forward now.
Guru says
Hi JH,
Spring bunnies can definitely be a pain and totally wipe out all your hard work. OA could be the way forwards. I’d be interested to hear how you got on. Also, I hear that rabbits are not fond of sulfur and that people sprinkle some around their plants. You could also try planting some onions, as the smell tends to keep rabbits at a distance.
Good luck!
Tom.