Happy International Pee on Earth Day

Applying urine to your garden may not be a silly idea

Applying urine to your garden may not be a silly idea

OPINION: A few years ago NZ Gardener magazine ran a survey asking readers for their best gardening tip - and one of the most popular pieces of advice was that we should use human urine in a diluted state as a free fertiliser for growing plants.

If you have ever been tempted to do this yourself, today is your day. Six-odd years ago June 21 was declared the International Pee on Earth Day by ecological wastewater expert Carol Steinfeld (also co-incidently the author of Liquid Gold: The Lore and Logic of Using Urine to Grow Plants).

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Applying dilute urine in the garden.
SuSanA Secretariat/Wikicommons

Applying dilute urine in the garden.


My time as editor of NZ Gardener has convinced me it's not actually that off-the-wall an idea. Human urine contains nitrogen, phosphorous and potassium as well as a few other trace elements that plants need to grow. Prof Walker, the much loved soil scientist who was a regular on Maggie's Garden Show, famously was an advocate of it and in the closing credits of one show was shown turning his back on the camera and unzipping his trousers to fertilise his sweetcorn. Roland Clark (who as 'Norwester' wrote many articles about trees and tree farming in agricultural and Tree Crops magazines) also was a fan of the practice: he would talk about his "source of portable nitrogen".

According to the Royal Horticultural Society Dictionary of Gardening urine is a good fertiliser as it contains not only small quantities of various salts, but also urea. With bacterial action this breaks down into water and ammonium carbonate, which in turn breaks down into ammonia, water and carbon dioxide. Adding gypsum coverts the ammonia into sulphate of ammonia, which is commonly used as a soil fertiliser (incidentally, the RHS guide specifically recommends urine, diluted with 3 or 4 parts of water for black currants and raspberries to help prevent diseases to which the plants are otherwise prone). 

The results of a trial using urine as a fertiliser on spinach. The crop on the left was fed with urine, the crops on the ...
Peter Morgan/Wikicommons

The results of a trial using urine as a fertiliser on spinach. The crop on the left was fed with urine, the crops on the right with water.

Pee on the Earth Day might sound frivolous, but there is a serious message behind it. Every person emits, on average, between 800ml and two litres of urine a day, and passes water an average of seven times. Every time you flush the loo you are using between five and 11-litres of drinking quality water, so Steinfield established the day to raise awareness around water usage.

She suggests marking the day by pee-cycling - whether you are making your contribution directly or using a discrete container that you can take outside after the act - and applying it to an area of soil or dirt (so not on concrete!) or directly onto your compost heap (urine is also a useful compost activator). If you want to use it on the plants in your garden, dilute it nine parts water to one part urine and spread it around - too much in one spot can risk burning plants' roots.

In fact it is only in very recent human history that we have been squeamish about urination. Human urine has so many practical applications that a few ancient societies actually used it as a trading currency, it was employed to soften leather, wash clothes, make soap, dye clothes and in the manufacture of gunpowder. The ancient Romans even used to gargle with it (the ammonia in urine cleans the teeth and gives you a brighter smile). Remembering that makes peeing outside sound positively pleasant - at least no one is suggesting you use urine as a mouthwash.

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Still not convinced? Maybe this heartfelt version of Miley Cyrus's Wrecking Ball, reworded so it's now about reusing urine as fertiliser, will convince you. And if you want to sing along with the chorus the words are: I wanna grow a garden/And I make all this nitrogen/I just need something to store it in/All I ever did was... flush it away/Yeah yeah you… you flush it away (be warned, it's a bit of an ear-worm).



 - NZ Gardener


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