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Pee on your plants: Human urine can be used as an effective and sustainable fertilizer

You’re probably flushing away a nutrient-rich, renewable fertilizer down the toilet every day: your pee.

Human urine can be used as a safe and effective crop fertilizer, researchers say. And studies show using pee as a substitute for commercial chemical fertilizers could have positive environmental impacts. 

“If you save all the urine that you produce in a day, there’s enough fertilizer in there to grow all the wheat that you need to make a loaf of bread,” said Abraham Noe-Hays, research director at Rich Earth Institute. “It’s a huge amount of nutrients, and it could grow a significant portion of our dietary needs just from from the nutrients in our urine.”

The Rich Earth Institute, based in Vermont, runs the country’s first community-scale urine recycling program and conducts research on the safety and efficacy of pee as a replacement for chemical fertilizers. One way the group collects pee from donors is by using urine-diverting toilets that keep the liquid separate from the solids. 

Urine contains essential nutrients such as nitrogen, potassium and phosphorus, all of which help plants grow and are commonly found in synthetic fertilizers, Noe-Hays said. 

But when our urine enters the wastewater system, those nutrients become pollutants because current water treatment infrastructure doesn’t totally remove them, causing environmental issues including harmful algal blooms. 

Chemical fertilizers also have their own environmental issues. A 2021 study found the production and use of synthetic nitrogen fertilizers accounts for 2.4% of global emissions, making it one of the most polluting industrial chemicals. 

Urine is “sustainable because we make it all the time,” Noe-Hays said. “We can’t stop making it and it has to go somewhere. So why not have it go where it’s useful?”

‘Pee for the peonies’ 

University of Michigan researcher Nancy Love recently applied pee-derived fertilizers on peonies at Ann Arbor school’s Nichols Arboretum as part of an effort to educate the public on the benefits of recycling urine. 

“It gives us an opportunity to have discussions with people about how nutrients flow through our communities, why it’s not sustainable, and why we need to start thinking differently,” Love, an environmental engineering professor, said.

Love and other researchers have been advancing urine-treatment technologies and studying people’s perception of pee-based fertilizers as part of a $3 million grant awarded in 2016 by the National Science Foundation. 

Some people, Love said, may initially be averse to the idea of recycling pee, but attitudes change once they’re given information on different fertilizers, including urine-derived ones.

For urine-derived fertilizer to become mainstream, Noe-Hays said, “it has to be with fixtures that people are familiar with and comfortable using. And we have to have a commercially available product for processing it and turning it into a usable fertilizer.”

Rich Earth Institute’s spin-off company, Rich Earth Tools LLC, is working on a system that can be used in buildings to capture urine to use as fertilizer.

It may take several years for urine-derived fertilizers to be used at a large scale, as researchers develop technologies, people’s attitudes change and a regulatory pathway for urine recycling is established, Love said. 

“It’ll be longer term than short term,” Love said, “but we have to be doing the work now to get us there.”

In the meantime, here’s how you can use pee in your home garden, according to Rich Earth Institute’s guide:

  • Collect your urine in a sealable and airtight container. To help with the smell, Rich Earth Institute recommends adding white vinegar or citric acid to the container before storing the urine.
  • Sanitize (if you need to). If you intend to share your crops outside your household, you should sanitize your urine by storing it in an airtight container at 68°F or higher for six months. You don’t need to sanitize the pee if no one outside the home is going to eat the crops, but use rubber gloves or wash your hands after handling urine. 
  • Fertilize your crops. Apply the urine directly to the ground, not as a spray. The World Health Organization recommends waiting at least one month after fertilization before harvesting your crops. 
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