As far as gardening trends go, the latest fad of sprinkling your beloved borders with pee is something of a divider. Where do you stand (or wee, as might be more apt), on the topic of urine for the garden?
Quite a question isn’t it? The use of human urine for fertilising the garden is nothing new, in fact it’s an age-old gardening technique that has been employed by the more passionate gardeners for centuries.
There are two sides to this garden practice and most people will fall into one of two categories – ‘Oh yes, definitely! And there’s lots of evidence to back it up.’ This is quickly appended with an insistent assurance along the lines of ‘I’m not mad though!’ Then there’s the other side of the argument – ‘Ew, what? No way.’ accompanied by a look of disbelief…and bewilderment…and horror.
So, when it comes to urine in the garden, what exactly is the lie of the land?
Well, fresh urine is actually completely sterile and thus free from bacteria – furthermore, it is essentially so clean that, technically, it could be drunk when fresh (though admittedly you’d have to be pretty thirsty to try).
It is only when urine is older than 24 hours that the urea turns into ammonia and develops that funky stale fragrance that we’ll affectionately call, eau de wee. By this point there’s no going back and the urine is not just unsuitable as an afternoon beverage but also too strong to use on plants.
That’s not to say it can’t be used on the compost heap – there’s no waste here! Adding urine, or urinating directly onto a compost heap, most definitely helps to activate the composting process and accelerate it. This is considered a completely safe and organic method for producing a healthy supply of organic matter.
But back to the fresh stuff, exactly what is it that makes our urine so influential in the garden?
A study titled Urinalysis in Clinical Laboratory Practice, published in 1975 by one Dr A. H. Free, outlines some of the critical nutrients found in urine, including urea nitrogen, urea, creatinine nitrogen, creatinine, uric acid nitrogen, ammonia nitrogen, amino nitrogen, sodium, potassium, calcium, magnesium, chloride, inorganic sulphate and inorganic phosphate.
Here comes the science
Healthy human urine is approximately 95% water, 2.5% a key substance called urea and another 2.5% a mixture of minerals, salts, hormones and enzymes. As such, human urine is actually one of the fastest-acting sources of potent nitrogen (mostly as urea), as well as dissolved phosphates and potassium – all of which are the main macronutrients required by plants.
The nastier and less productive concentrations of heavy metals such as lead, mercury, and cadmium, commonly found in faeces, are significantly lower in urine and therefore of very little cause for concern. In fact, the only currently observed problem with using human urine as a fertiliser is the potential for a build-up of excess nitrogen and inorganic salts such as sodium chloride, which also contribute to the wastes excreted by the renal system.
In short, science backs up the ‘oh yes, definitely’ argument but before you go relieving yourself onto your rose bush…
The changeable nitrogen and inorganic salt levels don’t necessarily mean it’s a no-go, but they do rely on the quantity and regularity of the use of urine, the tolerance of the plant and general soil condition, as well as the amount of rainfall and other forms of irrigation and fertilisation.
There is a very easy way around all of these manipulating factors though and that’s as simple as dilution.
After all, it’ll come as no surprise that undiluted urine can potentially burn the root of a plant and discolour grass – anyone with a dog will be able to vouch for the unwanted effect of excess nitrogen.
In the same way that this is precisely why you don’t need to dilute urine intended for use on the compost heap, it is exactly the reason that, should you choose to use your urine anywhere else in your garden, you should always dilute it first.
It is recommended that you dilute one part urine with approximately 10 parts water and always apply it directly to the plants root system. Dilution will also help to fend off any associated whiffs.
Which urine is best? Male v Female
Whilst some state that male urine is a superior form of fertiliser to female urine because it is less acidic, there is no scientific evidence to support any difference between the effectiveness of diluted male or female urine on the garden – so, logistics aside ladies, feel free to get involved!
From amateur trials, foxes tend to stay away from areas that have been sprayed with male urine. So if you are needing to keep a newly planted area fox free, try spraying some male urine around.
Word of warning: Should you decide to give it a go, we strongly advise that you use only healthy urine that is free from infection. Birth control and hormone supplements are widely considered unsafe for use. Supplements however, tend to present themselves in very low doses in the urine and would consequently have a negligible impact on the garden.