“Soil Your Undies” sounds like the latest, grossest internet challenge to make the social media rounds. But it’s actually a chance to get your hands dirty with a bit of citizen science. We wrote about this fun summer science project for the kids to learn about soil health in 2021, and it’s still a great idea. It could even help you make your garden grow a little lusher.

The Soil Your Undies challenge was simple, and nothing like what you’re probably thinking. The challenge is simply to bury a new pair of tighty-whities and dig them up eight weeks later. It’s an easy test of soil health based on the fact that cotton is biodegradable. In healthy soil, there won’t be much more than the elastic waistband of the underpants left after eight weeks. But in soil where the biome is weak, the (washed) underwear is still wearable after two months underground.

The science behind the spectacle is real. Cotton is almost pure cellulose, a carbon-rich food source that soil microbes devour wherever the underground ecosystem is thriving. One teaspoon of healthy soil can contain more microbes than there are people on the planet, according to the USDA’s Natural Resources Conservation Service — billions of bacteria, fungi, and other organisms that cycle nutrients, store water, and help soil resist erosion. The more chewed-up your undies come out, the more active that hidden workforce is.

Soil erosion and the loss of healthy topsoil are among the top environmental issues affecting farmers around the world. U.S. cropland loses an average of 4.63 tons of soil per acre per year — about 1.7 billion tons nationwide — according to the USDA-NRCS National Resources Inventory. And that figure leaves out tillage erosion: a University of Massachusetts Amherst study estimates the Midwest alone has shed roughly 57.6 billion metric tons of topsoil since farming began there about 160 years ago, eroding 10 to 1,000 times faster than soil naturally forms. Because rebuilding just an inch of topsoil can take centuries, simple tools that get people curious about what’s happening underground matter more than ever.

The “Soil Your Undies” challenge took root in Oregon as a project between farmers and their local Soil and Water Conservation Districts as a way to get the public interested in soil health. The NRCS Oregon Soil Health Committee gave the campaign a visual brand when it launched in December 2018, and more than 100 Oregon farmers, ranchers, and agricultural enthusiasts have since taken the challenge.

Corey Miller, a wheat farmer in Oregon, took the Soil Your Undies Challenge and discovered the richness of his no-till soil:

Oregon Undies Take Off Down Under

Almost immediately, Australian agriculturists and educators hopped on the pants-wagon, and the challenge took off down under. In most parts of the world, people leave a bit of elastic sticking out of the ground to mark their test site. But in Australia, the buried undies kept disappearing (kangaroos have been blamed) so down there they bury their samples completely. More than 400 farms and schools had participated in the challenge by April 2021.

What started as a few hundred buried pairs has become a full-fledged citizen science movement. Soil systems biologist Dr. Oliver Knox of the University of New England, working with Cotton Info and UNE’s outreach teams, has now run the challenge with more than 500 groups of farmers, schools, and Landcare groups. Along the way the program reached an estimated 12,000 schoolchildren across roughly 500 classrooms, work that earned Knox Landcare Australia’s General Jeffery Soil Health Award. The undies have even traveled further afield: Knox has helped adapt the method for farmers in Benin, West Africa, and Western Uganda, using pre-weighed cotton squares where underwear isn’t practical.

“Soil Your Undies” is easier and a lot more fun than taking scientific soil samples and reading soil chemistry test results. It’s also a simple way to illustrate the principle of biodegradation for kids. But surprisingly, it has actually led to meaningful changes. Some farmers who participated in the challenge have changed their land management methods to become more sustainable. If commercial farmers can be convinced to change their ways with this simple experiment, it could be just as useful for homeowners who think they need to spray for every bug.

The movement keeps spreading on this side of the world, too. Soil and water conservation districts, watershed councils, and university teams from Pennsylvania to Tennessee to Montana now run seasonal campaigns, often handing out free cotton undies and flag markers and inviting participants to add their results to a shared online map. The challenge has even become a science-fair staple. In early 2025, a fifth grader in California took first place at his district fair with a Soil Your Undies experiment.

Plant Your Pants

Bury your tighty-whities under about 3 inches of your garden’s topsoil. Assuming you don’t have a kangaroo problem, you can leave a bit of the waistband sticking out to mark the burial site. But using a creatively labeled plant marker might be more fun anyway. Wait two months, then dig them up.

For the cleanest comparison, try burying pairs in a few different spots at once — a composted bed versus a high-traffic, compacted patch, or an irrigated area versus a dry one. Soil scientists note that microbial activity is most visible when there’s good soil moisture, so the difference between a mulched, well-watered bed and bare, dry ground can be dramatic.

If you try this at home, make sure the underwear is 100% cotton. Polyester will not degrade in two months regardless of soil health. If you accidentally use a cotton blend, you’ll be illuminating another environmental issue – the need for sustainable underwear (and other clothing) that won’t live forever in a landfill.

It’s time to reignite Soil Your Undies, a great idea then, and now.

Editor’s Note: This article was first published by Gemma Alexander on June 21, 2021, and was updated in June 2026.

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