7 Genius Ways to Use Hydrogen Peroxide to Repel Pests and Boost Plant Health

Hydrogen peroxide is popularly used as a mild antiseptic, but it can also do wonders in the garden. It can improve soil quality, remove root rot, repel unwanted garden pests, and even enhance your chances of seed germination. Here, we share all the surprising ways to use hydrogen peroxide to boost the health of your indoor and outdoor plants.

Treat Fungal Infections

Powdery mildew and downy mildew are fungal infections that can be treated using hydrogen peroxide. "I have used hydrogen peroxide as a mist on leaves when I first see signs of powdery mildew," says Tammy Sons, a master gardener and founder of TN Nursery. "It is by no means a sure thing, but a low-cost, easy, and generally safe trick to have in your bag of tricks."

To treat plants suffering from downy or powdery mildew, create a 3:1 solution of water and 3 percent hydrogen peroxide. “Place this mixture in a spray bottle and use it to spray affected plants, including the underside of leaves,” says Lucie Bradley, a gardening and greenhouse expert at Easy Garden Irrigation. She recommends doing this in the early morning so that the solution can dry before the afternoon heat. Repeat this treatment every couple of days until the infection has gone.

Remove Root Rot

Potted plants can suffer from root rot when they are overwatered or experience poor drainage, but hydrogen peroxide can help remedy this issue. "The reason hydrogen peroxide can help with root rot is that when it decomposes, it releases oxygen and water," says Bradley. The increased oxygen improves aeration in the soil, giving roots more access to it, she says. To use hydrogen peroxide to treat root rot, remove the plant from its pot, loosen any soil around the roots, and use clean scissors to cut away infected roots. Then, use a 1:1 solution of 3 percent hydrogen peroxide and 1 part water to spray the roots thoroughly before potting the plant in new soil. 

Prepare Soil

Even if your potted plants don’t have root rot, it may be a good idea to treat their roots with hydrogen peroxide when transplanting. Sons says she uses a couple of tablespoons of hydrogen peroxide per quart of water when moving outdoor plants into pots or transplanting one potted plant into a new container. "I like to use it particularly with young delicate roots,” she says, “this gives them a little extra oxygen as they deal with transplant shock." But she warns that you shouldn’t over-use this solution; otherwise, you can damage plant roots, especially those of younger plants.

Eliminate Aphids

Spray a solution of hydrogen peroxide and water to help control and get rid of aphids. "Mix a solution of 1 part 3 percent hydrogen peroxide and 4 parts water," says Bradley. "Then add to a spray bottle and liberally spray the infested plant, ensuring you cover the aphids with the solution." For the best results, make sure the insects receive direct contact with the solution. The hydrogen peroxide will damage the aphids' exoskeleton.

Eradicate Fungus Gnats

You can use hydrogen peroxide to get rid of adult gnats, as well as their larvae and eggs. "To kill the eggs or larvae in your plant's soil, first let the soil dry out," says Bradley. Then, drench the soil using a 4:1 solution of water and 3 percent hydrogen peroxide. “You can repeat this process once a week until the infestation has gone,” she says. For the best results, aim for direct contact with the adult fungus gnats to kill the invading pests.

Encourage Seeds to Germinate

Gardeners often soak seeds before sowing to soften the seed coat, improving germination rates. "But you can also do this using a solution of 1 part 3 percent hydrogen peroxide and 8 parts water," says Bradley. Soak the seeds in this solution for 30 minutes to an hour, then rinse in water. Then soak in water for an additional 10 to 11 hours before sowing. "This works best with larger seeds, which would usually take weeks to germinate," she says. 

Sterilize Soil

Sterilizing soil with hydrogen peroxide will kill any bacteria and fungi. According to Bradley, there are two ways to do this. "For small amounts of soil—for example, houseplants—use a container where you have placed drainage holes in the base," she says. Then add the soil to the container and drench it with a 1:1 solution of 3 percent hydrogen peroxide and water. Mix the soil to ensure the solution is thoroughly combined. Once the soil is dry, you can use it for potting plants. 

For larger amounts of soil, spread a thin, 1/4-inch layer of soil over a plastic sheet. Then, spray with a solution of 1/2 a cup of 3 percent hydrogen peroxide and 1 gallon of water. Make sure all the soil is moist but not drenched, she warns. If needed, you can add another layer of soil and treat this layer. Once finished, leave the soil to dry for three to four hours, then use it for your gardening needs.