"I pee on the lawn to water the ladybirds..." Do you know the song? Well, it turns out it's making a comeback, and there's increasing talk about using urine in the garden. To be more precise, we're revisiting the idea that peeing in your garden to help plants grow (or just for fun!) was a common practice in the past, especially in rural areas.
But is it really effective? Can human urine replace our usual fertilisers? Is watering with pee a cure-all? Does it not bring diseases? Let's check all this out!
Urine as a fertiliser: a concentrate of nitrogen
Human urine is naturally rich in nitrogen. It can actually be used to correct nitrogen deficiency. To be precise, urine contains urea, which is reduced to ammonia gas NH3 (that's the smell!). This can, depending on temperature and soil biology, be further reduced to ammonium NH4+, which is good; or oxidised to nitrate NO3-, which is less desirable... But both of these chemical compounds can be directly absorbed by plant roots. They are part of what is known as the nitrogen cycle.
Urine also contains phosphorus, potassium, sulphur, magnesium, and various other trace elements.
The composition varies depending on the person's diet: nitrogen content ranges from 3 to 6 g/litre, while phosphorus and potassium average around 1 g/litre.
All this makes urine a balanced and readily absorbable fertiliser for plants.
But, like anything, it must be used correctly!
Urine in the vegetable garden
In well-amended soil (using compost or manure), the use of liquid fertiliser is not really necessary. However, urine can be used diluted at a rate of 100 ml in 1 litre of water, every two weeks during the plant growth phase.
Be careful not to give this "fertiliser" to seedlings or very young plants. They will then produce stems and foliage at the expense of the root system, causing problems later on. These plants will struggle to access water and nutrients and will be less resilient.
Urine in compost
Urine in compost accelerates the decomposition of organic matter.
However, in high doses, urine is toxic to earthworms, compost worms, and other living organisms in the soil. So, be sure to use urine sparingly or dilute it at a rate of 250 ml of urine to one litre of water at a minimum.
Urine in other parts of the garden
Urine is a powerful nitrogen fertiliser. Overdosing in certain areas of the garden will encourage the proliferation of nitrophilous plants: nettles and bindweed at the forefront. In some extreme cases, you could even "burn your plants". So, caution is advised...
If care has been taken to provide fertilisation at planting and to maintain a living and healthy soil, nitrogen fertiliser is rarely needed for ornamental plants: trees, bushes, and even perennials.
In pots or containers, however, it can be a good alternative to regular liquid fertilisers. Again, remember to dilute the urine: 50 to 100 ml of urine per litre of water. And only apply your mixture (or pee...) once every two weeks.
Urine? Yuck?
It's mainly in the West that we have reservations about using human and animal excretions. Urine is frequently used in Africa, Asia, and South America. Numerous agronomic studies are underway to quantify the real impact of this practice: so far, the results are more than encouraging.
Pee, it stinks!
Urine, even diluted, has an unpleasant smell during its decomposition. Storing it for a week will remedy this issue. On a healthy and balanced soil, the decomposition of urine will occur very quickly, which will limit the duration of this unpleasant odour.
Pee, it's not clean!
Urine is naturally sterile in a healthy person. However, avoid using the urine of someone with a bacterial infection in the vegetable garden: note that relatively long storage (at least a month) will eliminate any potential pathogens. Conversely, also avoid using urine from someone on medication, especially antibiotics.
Note: it should also be noted that urine can contribute to excessive salinity in sensitive soils.
Conclusion
If we can get past the repulsion of using our own excretions, urine can prove to be an effective fertiliser. However, keep in mind not to use it pure, not too often, and only when necessary. In short, the usual precautions for a genuine fertiliser! It's also ideal to store urine beforehand to avoid pathogens and significantly reduce the smell.
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