A Free Fertilizer (Gross-Out Warning!)

One of the toughest parts about growing a garden in the city is the lack of access to traditional fertilizers and other soil inputs -- we're talking about manure, for the most part. You just don't see a lot of cows, horses, or goats in Rodgers Forge yards, for better or worse.

However, if you have the stomach for it, there is a free fertilizer available to just about anyone who drinks liquid: urine. Yes, we said it, and we'll say it again: pee is good for your plants.

Or so we're told. With this post, we are not saying that you should use urine in your garden, and we're not even saying we use it in ours. We are merely presenting another view on the virtues of using a waste product for fun and profit in the garden. The bottom line here: If you're going to use urine in the garden, do so at your own risk.

OK, down to business.... We are not the first people to suggest using urine as a garden fertilizer. Many organic gardeners already know about the advantages of using urine, especially for "heavy feeders," or plants that require a lot of nutrients. A magazine as mainstream as U.S. News & World Report recently covered the, er, golden opportunities with urine. The story focused on the work of Finnish scientists, like Surendra K. Pradhan.

The "yuck" factor aside, scientists who used urine to help raise a bumper crop of cabbages said the practice may not be a bad idea....

The use of urine as fertilizer is uncommon, but it is increasing in some parts of Finland, the researchers said. It also has been used to fertilize barley and cucumbers, the study said. "We assume the nitrogen contents of human urine could be a good fertilizer for many other plants or crops," Pradhan said.

The researchers chose cabbage as a test crop, because it needs a lot of nitrogen, it is distributed worldwide, and it can be preserved as sauerkraut.

The cabbage fertilized with urine was compared with similar plots of cabbage that either went unfertilized or where commercial fertilizer was used. At harvest, the cabbage enriched with the urine had several advantages: It was slightly larger, it grew to its maximum size more quickly, and, for most of the growth cycle, it suffered less bug damage than the commercially fertilized variety....

As a result of the findings, the team concluded that urine produced by one person over a year would be enough to grow 160 cabbages -- that's 64 kilograms (141 pounds) more cabbage than could be grown in a similar plot fertilized with commercial fertilizer. They recommend collecting urine from eco-type toilets, storing it, then scattering it on the soil around the plants rather than directly on them.

Additionally, a growing number of people have been talking about the risks of "peak phosphorous" -- that is, the dwindling supply of a vital plant nutrient, which is now mined in various parts of the world. As it turns out, urine is a great source of phosphorous.

Both oil and phosphate rock are finite, non-renewable fossil resources that were created in deep geological time, whether from decaying biomass for oil or millennia of pooping seabirds for phosphate. But there are substitutes for oil; there is no substitute for phosphorus, an element that forms bones, sustains cell membranes and gives shape to the DNA and RNA in all living things.

“We are effectively addicted to phosphate rock,” said Dana Cordell, a Ph.D. candidate who works with White and co-authored the recent studies. Cordell’s thesis, The Story of Phosphorus: Sustainable Implications of Global Phosphorus Scarcity for Food Security, was published as an e-book by Linköping University in Sweden on Feb. 4.

“The quality of the remaining phosphate rock is declining,” Cordell said. “We’re going to have to shift away from our use of it. There is no single quick fix solution.”

Worldwide, according to Cordell and White, five times more phosphorus is being mined than is being consumed. Stated another way, 15 million tons of phosphorus is mined yearly to grow food, but 80 percent never reaches the dinner table: It is lost to inefficiency and waste....

Mature animals, including humans, excrete nearly 100 percent of the phosphorus they consume. But only half of animal manure — the largest organic and renewable source of phosphorus — is being recycled back onto farmland worldwide, studies show. And only 10 percent of what humans excrete is returned to agriculture as sludge or wastewater.

“We need to start talking about our pee and poo more seriously,” Cordell said. “We need to be thinking in terms of 50 to 100 years.”

So, those are some of the arguments for using pee in the garden. Now, here's how most people suggest using it: Collect the stuff in a vessel, like a watering can, and dilute it -- at least eight parts water to one part urine. (Pure urine could burn your plants, experts say.)

Also, we would suggest pouring it at the roots and not on the plants that you plan to eat whole, like salad greens. That's just gross. Urine is said to be sterile in most people, so contamination tends not to be a problem.

One more thing: If you're eating a high-salt diet or consuming medications that could pass through your body and into your urine, it's probably best not to use urine at all.