Why And How People Use Hydrogen Peroxide For Greenhouse Soil (& Should You Try It?)

One of the many advantages of growing plants in a greenhouse is that you control the soil quality. Adding purchased soil to raised beds, pots, or even directly to the floor of the greenhouse keeps it relatively free from pests and diseases. However, after a few seasons, it can be hard to keep this same soil in ideal conditions. Sneaky bugs and airborne diseases can make their way through your greenhouse's ventilation system or on plants started in different environments. Hydrogen peroxide is a powerful cleaning tool for greenhouse surfaces, but how about using it for cleaning your greenhouse's soil? Are there other purported benefits of hydrogen peroxide for soil?

Home gardeners share the miracles of hydrogen peroxide for soil on social media. They claim that soaking soil in diluted solutions supposedly nips fungus gnats in the bud, and an undiluted 3% solution can conquer a bit of mold. However, take these anecdotal sources with several grains of salt. Luckily, certified smarty pantses have been hard at work testing hydrogen peroxide's benefits on soil as well. It turns out that there's some solid data to back up these claims, along with some other interesting findings. With the right dilution and application, hydrogen peroxide could be your new favorite way to refresh your greenhouse soil.

There are brilliant ways to use hydrogen peroxide in the garden, so why not in the greenhouse, too? TikTok and YouTube are teeming with vids boasting hydrogen peroxide-purified soil. @andrethefarmer suggests a spritz with a 1:1 water to hydrogen peroxide mix can tackle a moldy crust on a seedling tray. The same ratios do away with algae on soil surfaces or unwanted arthropods squirming around. A more dilute solution drowns out fungus gnats, according to mtplanters. Other online gardeners boast that hydrogen peroxide kills some nematodes and even acts as a fertilizer.

Each video shows convincing results, and other home gardeners share similar successes in the comments. These gardeners confidently pour diluted mixtures on soil complete with resident plants. However, not everyone reports their desired outcome. Skeptical commenters worry that the hydrogen peroxide will kill beneficial soil microorganisms, and others lament that their seedlings died after trying this trick. Outside of a controlled environment, these results don't hold a lot of water (pardon the garden pun), and proof that some of these miracle cures work is hard to find. Yet reliable sources support quite a few of these seemingly homespun remedies to a certain degree. But is it enough to convince you to treat your greenhouse soil with a bit of the brown-bottled stuff?

There have been scientific studies on the effects of hydrogen peroxide on soil, and some are promising. It's been shown to fight fungi and diseases. Hydrogen peroxide knocks out algae in water and on hard surfaces, so it may also be effective at ridding algae from soil. Researchers at China's Huanghai University discovered that a 4.5% hydrogen peroxide solution in soil eliminated a major ailment on apple trees as well as some undesirable fungi in soil. New Zealand's plant supply store, Love That Leaf, shares that different concentrations of hydrogen peroxide can clear up problems like fungus gnats and diseases that cause root rot.

Diluted hydrogen peroxide can also help aerate greenhouse soil. For fluffy growing medium that allows good air circulation, Howard Garrett, also known as The Dirt Doctor, advises stirring one 32-ounce bottle of 3% hydrogen peroxide into one gallon of water to treat 1,000 square feet of soil. However, other studies have found limited benefits to applying hydrogen peroxide to soil. Because it breaks down very quickly on the soil's surface, that limits the chemical's effectiveness for treating diseases, pests, and other problems. 

You may find that the evidence is tempting enough to douse your soil with hydrogen peroxide. The university studies don't share exact recipes for a soil treatment, but the proportions of water to hydrogen peroxide shared by Howard Garrett may be worth a go for prepping your greenhouse soil.