Among the items in many home first aid kits is a bottle of hydrogen peroxide,a popular treatment for minor cuts, scrapes or burns. Turns out, what’s good for your wounds may also be good for your plants.
Hydrogen peroxide prevents and controls bacteria and fungi, and is approved by the U.S. Environmental Protection Agency to control pests on both outdoor and indoor plants.
It’s an affordable and easy to find solution that many in the gardening world swear by as a treatment for pests, especially fungus gnats commonly found on houseplants.
Because hydrogen peroxide breaks down rapidly in the environment into oxygen and water, the EPA maintains there are no likely risks to humans or the environment when product label instructions are followed completely.
This agricultural form of hydrogen peroxide approved by the EPA is different from the kind you buy at the pharmacy, according to Kerry Bernard, of the University of Maine Cooperative Extension pesticide safety education program. Pharmaceutical hydrogen peroxide has not been tested or approved for use on plants, she said.
The recommended garden agricultural hydrogen peroxide products can be found at most farm supply and gardening stores. But Kris Graham, a garden and nursery manager in Scarborough, said she has been using household hydrogen peroxide on her plants with no ill effects.
Fungus gnats are attracted to the moisture in potting soil and where an adult female will lay about 200 eggs. After hatching, the gnat larvae burrow into the potting soil feeding on fungi and decaying plant material.
While harmless to humans, an infestation of fungus gnats can damage houseplant root systems and spread plant diseases.
“Hydrogen peroxide can be a helpful tool in certain situations,” Graham said. “But like anything, [when] adding something to plants that is not natural, there are good ways to do it and not good ways to do it.”
Graham is speaking to pharmaceutical hydrogen peroxide and said she has used it successfully to control fungus gnats on her own house plants over the years.
What is important to keep in mind, Graham said, is what hydrogen peroxide is intended for — to kill microbes and bacteria and sterilize whatever it touches.
“There are microbes that are important in the soil to keep your plants healthy,” Graham said. “Having living stuff in your soil is generally a good thing for the plant’s immune system and creating nutrients.”
That’s why Graham recommends using hydrogen peroxide only on indoor plants.
“Inside, your plants won’t be dealing with things that will harm their health if the microbes or nutrients are killed,” she said. “Outside, you have a lot of external factors that can harm your plants so you don’t want to mess with their immunity.”
Indoors, Graham uses hydrogen peroxide for one specific pest.
“I use [pharmaceutical] hydrogen peroxide indoors if I have a fungus gnat problem,” Graham said. “It can kill the larvae.”
She starts with a solution of one part hydrogen peroxide to four parts water in a container large enough for the potted plant. The solution should be several inches deep and the plant should be left in it between 15-and 30-minutes so the soil can draw up the liquid through the drain hole in the bottom of its vase or pot.
The process is a treatment, not a gnat preventative, Graham said, and it may have to be repeated two or three times before the insects or totally eradicated from the plant.
It’s not a bad idea to give your houseplants a bit of fertilizer or even new potting soil after multiple hydrogen peroxide treatments, Graham said.
Using pharmaceutical hydrogen peroxide as a gnat control may be popular and produce desired effects, but Bernard said the science does not support it. Bernard actually recommends against doing so.
“It’s never wise to make your own pesticides or use a chemical as a pesticide that isn’t labeled for that particular use,” Bernard said. “Ready-to-use EPA-approved products should pose very little risk when used according to label directions.”
For those not wanting to use chemicals on pests like the fungus gnat, Bernard said there are alternatives that are just as safe.
“You can let the plant’s soil dry out,” she said. “That will get rid of the fungus gnats and then you can repot your plants in clean soil.”