Taking the pee: is urine a good fertiliser?

Many of us consider it a waste product but, in fact, is urine a good fertiliser? Scarlett Penn of WWOOF UK sets out why we should pause for thought before we flush.

Many of us consider our urine to be a waste product, which we flush out of our lives with purified drinking water. Even with a low-flush toilet the average person may use about 40L of treated water a day to whisk away their wee. The eco and cash cost of sanitising water for drinking is huge, so to recklessly contaminate and flush it is, in both senses, taking the piss.

But in fact, just like when we discard our manure into the sewage system, we’re flushing away one valuable resource with another. And what’s even less widely known is that a majority of beneficial land nutrients leave the body with urine, not faeces.

credit: Michigan Tech

Urine is 95% water but it’s what’s in that other 5% that’s important. 2.5% is urea, a nitrogen-rich organic compound formed from the breakdown of protein in the human body. The remaining 2.5% is minerals such as potassium and phosphorous and other dissolved ions, salts, hormones, other compounds and metabolites.

So, we’re saying urine is a rich source of nitrogen (N), plus it contains phosphorus (P) and potassium (K). If you have anything to do with farming or growing you’ll be familiar with these initials as the triplet of macro-nutrients essential for plants to grow well. You’ll see sacks of artificial fertilisers with a dizzying array of numbers to signify their ratios and concentrations of N:P:K (20-5-5 or 10-10-10 for example).

The NPK ratio of human urine varies with diet and each person has a unique profile within that but roughly speaking, an average westerner will produce urine with the proportions at 11:2:4. This means:

• your pee is a high quality fertiliser, rich in nitrogen, which can be applied directly to your soil

• it’s local, readily available and plentiful – one person’s urine is enough to benefit a tenth of an acre plot for one whole season

• it’s fast acting because it’s in a ready-mixed form perfect for your plants to have a hearty drink, absorb and use straight away

• it’s safe and sterile – most urine is urine is pathogen free unless you have a serious infection. If you have doubts, consider the planetary risk of the alternative because…

• to produce nitrogen artificially involves the industrial fossil-fuel and energy hungry Haber-Bosch process

• With an expanding population producing more of this rich source of nitrogen, if our wee went in our waterways without being treated at a sewage plant, it would contribute to eutrophication (algal blooms) in which will in turn kill animals and plants due to lack of oxygen.

• and it’s FREE

So what’s holding you back from doing your pee-cycling? Let’s be clear, any ewwwwww! or gross-out factor is cultural programming. We’re perfectly happy to use animal poo (rebranded as garden manure), why not human wee? It’s been used for thousands of years but fertiliser manufacturers don’t want to you to know that. They also don’t want you to know many fertilisers are made from dried animal pee.

But wait, pull up that pelvic floor! Before you rush out to tinkle on the tomatoes here are some important dos and don’ts.

Dilution is the solution

Your pee pH is likely to be on the mildly acidic side, perhaps about 6. With our Western diet, it’s also likely to contain a lot of salt. These things can scald and harm microorganisms and delicate root systems, so you need to dilute your salute with water. Advice varies between a 1:5 and 1:15 dilution, but generally use a gentler mix for younger or more sensitive plants.You’ll need to do a degree of experimentation to see what works for your own particular circumstances but some general rules apply. Add your liquid gold to the soil, not to the leaves (a foliar feed, in growers’ terms) as it can burn them. You will see the leaves will go a really dark, rich green after a good soil application. Don’t overdo it as it’s deceptively potent stuff. If you eat a lot of salty foods you might want to thin further, especially if the land is parched or climate arid. If you don’t, sometimes salt can accumulate in white crystals on the garden which is harmful for the plants you’re trying to nurture.

pee rainbow – diet, drugs and illness make a difference. credit: Heather West

Are you on drugs?

Think twice before taking a leak on your leeks if you’re on recreational drugs or medication; pharmaceuticals or by products can go through you and into the soil. And if you have any funky goings-on downstairs don’t put your pee to veg garden use. If you really want to avoid flushing, try going in a hedgerow to fertilise your fuel crop, or perhaps on the compost heap where the very act of peeing will accelerate decomposition and the heat cycle eliminate bacteria.

Don’t pee on the peas please

Leguminous (nitrogen fixing) plants such as beans and peas have access to enough nitrogen so while it won’t harm them, you’ll get better effects elsewhere. You might also want to consider holding back on plants where lots of green leaf may come at the expense of the crop e.g. carrots. Urine is so rich in nitrogen it’s great for plants where you’re trying to encourage green leaves and also seeds, such as cereal crops. However it’s relatively low in potassium, which is also very easily fixed for free. Simply add wood ash (N:P:K ratio of 0:1:3, plus contains lots of calcium) stir, et voilà , the perfect fertiliser for plants which are set to produce more in the way of flowers, fruits and roots.

The angle of the dangle

You can collect your golden wonder by using urine separating toilets, by going in a bucket, or – if you’re going to store it – using a funnel or natural male attributes to insert contents directly into a screw cap container. It can be stored as long as there’s an air tight seal but if you can smell stale urine your precious nitrogen is leaving as ammonia, a breakdown process which starts after 24 hours. At this point it’s stronger, so some say it’s best put straight on to the compost heap rather than onto your soil

Can I have a P please, Bob? (only people over 35 will get this)

It may be considered polite to inform or get permission from the people you’re serving up your piddle-powered produce to. But don’t be shy, get the family involved and induct your kids into this healthy habit an early age.

The positive results have been documented, for example a study with beetroot by the University of Kuopio, Finland here. A 2007 study of cabbages fed with human urine grew much better than those fed artificial fertilisers and in addition, suffered less insect predation. Trials with chard in Africa showed the same effect.

With all these benefits, why would you not consider closing the nutrient cycle and feeling more in touch with your earth, and getting more out of it? Don’t let your wee be a waste stream – start tapping into this golden opportunity right now!

About the author

Scarlett Penn used to live at Redfield Community, and is the Chief Executive of WWOOF UK. When she’s not travelling around in her big yellow van, she lives in Shropshire on a smallholding with her partner. She also looks after the Plants section of our website.