Colleen Vanderlinden


I read a post by Josh here on Planet Green about using urine in the garden. One of the commenters stated that using urine was completely unsanitary, which is a common statement when the subject of human waste comes up. Earlier in the day, I read an article from Mother Jones about the value of using urine as an organic fertilizer. It appears that we Americans are way behind in recognizing the agricultural value of urine. From the Mother Jones article: "For more than a decade, 130 households in Stockholm, Sweden, have collected their urine--nearly 40,000 gallons of it per year--and trucked it off to be sprayed on crops. More than 600,000 Chinese households in at least 17 provinces use special urine-diverting toilets to fertilize crops such as sugarcane, watermelons, and peanuts. Farming communities in 17 African countries have also taken up the practice of collecting urine. And in the central Mexican village of Tepoztlán, an environmental group wheels a urine-collecting porta-potty to fiestas and uses the cache on local fields."

Human urine is a very high-quality fertilizer. It is so high-quality, in fact, that a single person's urine would be enough to fertilize up to one tenth of an acre of vegetables for an entire year. There is a certain grossness factor that would undoubtedly turn some people off of the whole idea of using urine on their veggie garden, but before we blow this off as just one more outlandish idea, let's look at what's really going on here.

Set aside the issue of bodily fluids and letting them loose in the garden for a moment. Let's look at what good fertilizers consist of. On any bag of either synthetic or organic fertilizer you would buy, there are three numbers commonly known as the NPK ratio.

  • N stands for nitrogen, which is important for stem and leaf development.
  • P stanks for phosphorous, which aids root development, as well as flower and fruit production.
  • K stands for potassium, which provides for general overall plant health and disease-resistance.

While I have yet to see an NPK ratio for human urine, we do know that it is high in nitrogen, and also provides good doses of phosphorous and potassium. In fact, in a 2007 Washington Post story, they followed a study in which human urine was used to fertilize cabbage (cabbage was chosen because it requires a lot of nitrogen for strong growth). The study found that the cabbages fertilized with human urine were larger at harvest, grew to their maximum size more quickly, and suffered less insect damage than cabbages grown with conventional fertilizers.

One concern that has been raised about using urine as a fertilizer, especially for edible crops, is that any pharmaceuticals that a person is taking could be passed along to the soil and plants via the urine. In the Washington Post story, one of the lead scientists in the cabbage study said that any pathogens that survived in the urine would have to battle it out with microorganisms that already exist in the soil. He also said that, most likely, those pathogens would lose.