We Asked Gardeners If You Should Use Hydrogen Peroxide on Plants—And We’re Trying This ASAP

Sometimes, unexpected household items can be useful in the garden, like hydrogen peroxide. Best known for being for first aid, the chemical compound can also be used to deter pests and disease in the garden.

“I like to keep a brown bottle of hydrogen peroxide on a shelf in my garage with my other gardening supplies,” Tabar Gifford, a master gardener and partnership cultivator at American Meadows and High Country Gardens, says. “It’s not a miracle cure, but it’s one of those inexpensive, reliable tools I’ve learned to reach for when a plant needs a little extra help.”

So, how can you best use this household staple to help your plants? We talked to two gardening experts about how hydrogen peroxide can be best used.

Why Use Hydrogen Peroxide in the Garden?

Experts say the chemical compound can be used in the garden for cleaning trays and pots, treating powdery mildew, sanitizing diseased plants, and even saving overwatered ones.

Hydrogen peroxide is an antiseptic that can eliminate lots of different bacteria, but to use it, you will need to dilute it first.

“Peroxide is just water with an extra oxygen molecule,” she says. “When it breaks down, it releases that oxygen, making conditions tough for fungal spores and harmful bacteria. That little burst of oxygen can even help stressed roots breathe a bit easier.”

Hydrogen peroxide can even help sanitize and rid young seedlings of disease, giving them the chance to grow, as Gifford experienced.

“Years ago, I lost an entire tray of zinnia seedlings to damping-off disease practically overnight,” she says. “A gardening friend suggested I sterilize my seed trays with diluted hydrogen peroxide before replanting, and I haven’t lost a tray since.”

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More Benefits to Using Hydrogen Peroxide in the Garden

On top of being anti-bacterial, hydrogen peroxide can also be used to ward off pests—specifically, fungus gnats.

Dr. James S. Mastaler, the founder of Pistils & Pollen, dilutes the liquid and uses it on the top layer of the infected plant’s soil.

He notes that it’s not his “first line of defense” against the bugs, but it works in a pinch.

“This helps kill off gnat larvae in the soil without harming the plant,” he says. “Hydrogen peroxide is something I keep in my pest management toolkit and return to from time to time—especially in low-pressure infestations or when I need a quick intervention.”

How to Dilute Hydrogen Peroxide

To use hydrogen peroxide, Gifford says the trick is getting the dilution right—and that may vary depending on what you’re using the antiseptic solution for.

• For getting rid of fungus gnats: Mastaler dilutes one part three percent hydrogen peroxide to four parts water to saturate the soil’s top layer.
• For watering stressed roots: Gifford suggests mixing two tablespoons of three percent hydrogen peroxide per quart of water and pouring it at the base of the plant.
• For spraying infected leaves: Gifford recommends using one teaspoon per cup of water with a drop of dish soap to help it stick.
• For cleaning gardening tools and trays: Gifford uses the chemical compound at full strength.

Before using the solution to treat your plants, Gifford recommends testing it on your plant first to make sure the strong substance doesn’t harm it.

“I always test sprays on one leaf first because some plants can be sensitive,” she says. “And I don’t use it as a regular treatment—just as needed—because overusing peroxide can disrupt the beneficial microbes in the soil that plants depend on.”