Fertilizing with human urine

Using human urine can help us work toward a closed-loop fertility system. While not a plant-based technique per se, using their own urine is a way that veganic gardeners can cycle back the nutrients from the foods they consume, while also diverting their urine from the water system where it acts as a pollutant.

Nutrients in human urine

When we eat food, our kidneys filter out excess nutrients that our body is unable to use, and these nutrients are then expelled from the body in our urine. Our urine contains significant levels of nitrogen, as well as phosphorous and potassium (typically an N-P-K ratio around 11 – 1 – 2.5, similar to commercial fertilizers). Americans produce about 90 million gallons of urine a day, containing about 7 million pounds of nitrogen. Studies conducted in Sweden (Sundberg, 1995; Drangert, 1997) show that an adult’s urine contains enough nutrients to fertilize 50-100% of the crops needed to feed one adult. Rather than importing nutrients for gardening, and exporting nutrients via the toilet, we can help close this loop by keeping our urine in the local food cycle. It can be especially beneficial for fertilizing in city environments where other local forms of fertility may be scarce due to lack of green spaces.

The truth about flushing

The high nitrogen levels in urine are favorable for plant growth, though this can actually pose a major environmental hazard when we flush urine down the toilet into the public water systems. After we flush, part of the nitrogen is removed during an energy-intensive denitrification process. The remaining nitrogen often makes its way to natural waterways, where it can off-balance the ecosystems through a process called eutrophication: the excess nitrogen causes increased algae and aquatic plant growth, and as these plants decompose it depletes the oxygen supply that is needed by aquatic animals, often causing death. So it’s preferable to cycle the nutrients in our urine through terrestrial environments rather than aquatic environments, by fertilizing trees, bushes, wildflowers, lawns, and even our gardens.

Is it safe for our health?

Is urine safe to use in our gardens? Pretty much. In healthy populations, human urine is almost always sterile. In the rare cases when it isn’t sterile, urine is generally still fine for personal use, or can be stored for several months to minimize pathogen risk. But you don’t have to take our word for it: there are detailed resources available that give comprehensive information. The following is intended to be a brief and non-exhaustive overview of health concerns and solutions, though we ask that people do their own research and draw their own conclusions.

Health concerns and solutions:

  • Avoiding fecal contamination: this is the most important element in the safe use of urine. While pee is almost always sterile, feces contains dangerous pathogens. Make sure that you get a 100% stream of pure urine. Special toilets are available that will separate your urine and divert it into a holding tank, though a simple plastic jug probably works even better to avoid any chance of fecal contamination. You can also store urine in a sealed container for several months to minimize any potential pathogens. (Sidenote: feces can be made safe for gardening through a specific composting process described in the Humanure Handbook, though should otherwise be completely avoided in gardening).
  • Avoiding illness: If someone has a urinary tract infection, or is using medications, they should avoid using their urine in edible gardens. Though there are still advantages to using the urine on lawns or landscaping, to avoid sending it to aquatic environments.
  • Individual use: Urine is considered quite safe for individual use. Our urine is probably sterile, and even if it’s not, we can’t catch anything from our own urine that we don’t already have. It’s recommended that after applying urine, we wait a month before eating the crops as a simple precaution.
  • Group use: When mixing urine from multiple people, again, it’s probably sterile, though there is more chance of pathogens, especially from accidental fecal contamination. Store the urine for 6 months in a sealed container before using it, and wait another month before eating the food crops as an added precaution.
  • Being extra safe and socially acceptable: Where safety and social acceptability are concerns for the user, there are a variety of ways of cycling the nutrients from urine. For those who choose to fertilize fruit and vegetable gardens, most people would focus on fruit-bearing crops like tomatoes and cucumbers rather than peeing by the root vegetables. Or, we can fertilize perennial plants like bushes and trees with urine, and later use the plants’ leaves in our compost pile or as a mulch, as a very safe and socially-acceptable way to cycle the nutrients back to our gardens. Or, when cycling our urine for environmental reasons, there’s no need to add it to our food crops: it can just as easily be applied to non-edible plants, like trees, wildflowers, lawns and landscaping projects.

Container gardens that occasionally receive watered-down pee

Using pee: A how-to guide

Keep in mind that urine is very high in nitrogen. You may need to pee daily, but your plants don’t need your daily pee. Choose plants that need lots of nitrogen, such as corn and squash, tomatoes and cucumbers during their fruit-bearing stage, and older plants that need a boost. Signs of nitrogen deficiency include yellow or pale green leaves, and some plants have key signs, like pointed cucumbers. Don’t overdo it at the beginning of the season, as excess nitrogen can lead to bushy, leafy plants that bear little fruit. Signs of excess nitrogen include curled leaves, and these plants may also attract aphids. For garden plants in need of a genuine nitrogen boost, once or twice a month is generally fine, though some people will add highly diluted pee a couple of times a week. If you have more pee to give, try your lawn, trees and bushes.

As a basic premise, the urine must be mixed with carbon-rich materials in order for the nitrogen to become accessible to the plants. Carbon-rich materials can include leaves, straw, or just good quality earthy soil. The nitrogen in urine is in the form of urea, creatine, and ammonia; when mixed with carbon-rich materials, the aerobic bacteria convert it into nitrates, which the plants can then uptake.

Here are a few possible ways to use pee in your garden or landscaping. Please read the safety guidelines too.

  • Recipe 1: Watered-down pee
    For soil with good drainage that is crumbly and earthy-smelling. Also works well for container gardens.

    Grab a reclaimed plastic container and take a pee. Dilute it with eight to ten parts water, and apply it to the soil. Easy peesy. Working the urine into the soil or applying the urine under the top layer of soil would ensure that less nitrogen is lost due to conversion to ammonia gas, and the presence of soil organisms would help neutralize the (rare chance of) pathogens, though just pouring it on the soil works okay too. After applying the pee, water the plant.

  • Recipe 2: Straight up pee
    For soil with a thick layer of carbon-rich mulch, like wood chips and leaf mulch.

    This is the easiest method. Just pee on the mulch. The mulch will stop the plants from receiving an overly-concentrated blast of urine, as well as helping to break down the nitrogen into a source the plants can use. Peeing between two layers of mulch will lessen nitrogen losses from conversion to ammonia gas.

  • Recipe 3: Compost pee
    Urine can be composted. It’s very high in nitrogen, so it counts as a "green" in the compost, and shouldn’t be added to a compost bin that is already high in nitrogen-rich materials like food scraps. Be sure to add plenty of carbon-rich materials, like dry leaves, sawdust, straw and cardboard. Urine can act as a starter for a compost, encouraging the decomposition process, such as adding urine to a pile of leaves.
  • Recipe 4: Straw bale bathroom
    You can urinate directly on a bale of straw until the straw decomposes, and this compost can later be added to your garden. We’ve even met a gardener from Montreal who plants directly in the decomposing straw bales to create a new garden.
  • Recipe 5: Greywater with a hint of yellow
    Greywater is the waste water from showering, doing dishes, etc, and urine can be added to a greywater system. The greywater provides some carbon and significantly dilutes the urine. Ideally this should drain into an aerobic greywater system with natural filters like plants and gravel. Instructions for installing such a system can be purchased from the EcoWaters Project in the guide How to Build a Washwater Garden Plan.

Keep in mind: Urine is high in salt. This is one reason why it needs to be properly diluted. Not all plants respond well to high salt content. Reducing the salt in your diet can be helpful to your own health and improve the salt ratio in your urine.

Is it good for our gardens?

Pretty much. As long as we don’t add excessive amounts.

Like all liquid nutrient sources, this shouldn’t become the primary form of fertility for our gardens. In natural ecosystems the soil organisms break down organic matter, like leaves and food scraps, and make the nutrients accessible to plants: this is nature’s digestive system. Liquid feeds (including urine, compost teas, chemical fertilizers...) bypass this natural system and feed the plants directly, much like a human receiving a liquid diet through an intravenous tube rather than eating lunch. We need to provide the soil organisms with organic matter in order to keep the soil healthy and biodiverse. So in general, liquid feeds should only be used as a complement to other forms of fertility, such as compost and mulch. On the upside, adding a little urine can help activate the decomposition of organic matter, so a wee bit of pee here and there is fine.

Adding too much urine can also affect plant health. Ever see a yellow patch on a lawn because a dog keeps peeing in the same spot? Too much nitrogen; it burns the plant roots. However, the reverse is true, that a lawn that is yellow because of a lack of nitrogen can have green patches where the dog pees. So, in order for urine to be helpful, we need to be observant of our gardens and moderate how much we apply.

Is this even veganic?

Sort of. That depends how you look at it.

Using human urine isn’t a “plant-based technique,” so in its purest form it can’t be considered “plant-based growing”. Though, all veganic gardens naturally contain free-living animals, like microorganisms, earthworms, and birds, who eat organic matter and create “micro-manure” as part of their normal daily life. So while veganic growing excludes the addition of waste products from animals that have been bred and raised, humans can be seen as “free-living animals” who voluntarily contribute their waste. This can also help reestablish humans as contributing members of a local ecosystem, rather than separating ourselves (and our bodily waste) through mechanized processes.

Here at the Veganic Agriculture Network, we keep our large countryside garden completely plant-based, to produce veganic food without the addition of any animal products (human or non-human). In the city, we use a little of our urine in our balcony container gardens to provide additional fertility to the plants, and to avoid the occasional flush in a highly urban environment.

Is urine gross? Does it smell?

Despite urine having an “ick” factor in many modern cultures, it’s been used throughout history for a variety of purposes, including cleaning wounds, making bread, and in the process of dying clothing. There are even people who drink their own urine on a regular basis. While there are good reasons to be cautious around feces, urine is generally sterile and fine to use for a variety of purposes. To learn more about the history and culture of urine, see Liquid Gold and Life of Pee.

Urine does sometimes smell. There really isn’t much problem if you use it immediately, especially if you dilute it. If you choose to store the urine (i.e. to eliminate potential pathogens) keep it in a closed container to reduce the smell. When applying it to the soil, it can help to slightly bury the urine in the soil or under mulch. We’ve used diluted urine in container gardens on a balcony for quite some time, and the neighbors haven’t even noticed.

Is it allowed?

For home gardens it should be fine, especially if you keep it low-key, but what about commercial farms? In some countries urine is accepted in commercial farming, such as Sweden, where it’s even applied mechanically to large-scale farms. The regulations vary from country to country, and using human urine could also affect the certification status of a farm. So if you are a commercial farmer, please contact the relevant local services to learn whether urine is an acceptable soil amendment in your region.

Further resources

Online resources

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9 January 2012
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