Is Urine Safe to Use in the Garden?

Is urine in the garden a match made in heaven or hell on earth?

Human urine is not commonly used as a fertilizer but we do use animal urine when it’s mixed with manure. Many gardeners have no issue with its use this way, but few would use human urine even if it is clean and free of feces. Is this just due to social attitudes or are there some a good reasons for not using urine. Is it safe? Will it burn plants? Can it spread human pathogens and what about all the drugs we use? Those can’t be good for plants?

Let’s have a wee look at using urine in the garden.

We Can Learn from Nepal

Urine is not used very much as a fertilizer in North American or Europe, but it is used in other countries like Nepal. Here is what Maharjan, a farmer from Nepal says about his organic vegetables.

“Urine also enhances the taste and quality of the vegetables”. “That’s why when I go to the market to sell, people come to me, and they don’t mind paying a few rupees extra.”

Concerns About Using Urine in the Garden

Gardeners have a number of concerns about using urine.

• Urine will make my garden smell like a subway – actually the smell goes away almost instantly when you pour it on soil.
• All the drugs and chemicals in my pee are going to kill the soil life! – a chemophobic reaction that is simply not true.
• Urine can transmit diseases – this is possible, but if you are using urine from your household you are already exposures.

One blogger wrote : “My pee is like the fine wine of pees. I eat nearly all organic vegetables that I grow myself. My diet also mostly consists of vegetables and fruit. The meat I do eat comes from our homestead or farmers I’ve personally vetted.” – Nonsense! An organic diet does not make urine better. Making urine is your bodies way of removing unwanted chemicals from the body. Almost all of these are natural and organic and come from vegetables as much as meat.

Nutrients in Human Urine

Common claims like “urine is a rich source of nitrogen, phosphate, potassium and micronutrients” are simply not true but it does have low levels of nutrients.

Urine contains 0.9% urea, or about 0.4% nitrogen. It also contains 0.1% potassium and 0.05% phosphate so it’s fertilizer NPK is 0.4 – 0.05 – 0.1. The actual values vary quite a bit and are affected by diet and the amount of water consumed. The pH is around 6.2 with a range of 5.5-7.0. At best this is a weak fertilizer with nutrients in the same range as kelp fertilizer.

A number of sites report that “Urine contains a nitrogen-phosphorus-potassium (N-P-K) ratio of 10:1:4”. This statement is not technically wrong but it will mislead some readers. This is a RATIO – not an NPK value. An NPK value is the actual amount in the bottle. A ratio ignores the actual amount you have, which in this case makes the amount of nutrients look bigger. Maybe this is why some bloggers report high nitrogen levels?

Unfortunately, it also contains 0.2% sodium which can be toxic to plants. The small amount of phosphate is in plant available forms but it can precipitate out during storage.

According to the Stockholm Environment Institute, “a person can produce enough urine per year to fertilize 300-400 square meters or roughly 3200-4300 square feet of crops”. Used at a household level, the urine a family produces is more than enough to help sustain a home garden.

Everything in this post deals with human urine unless stated otherwise.

Does Urine Work as a Fertilizer?

Humans have been fertilizing with urine for 6,000 years and we continue to use animal urine, which is not very different.

A study in Finland tested urine as a fertilizer on cabbage and found “the urine-fertilized plants grew slightly larger than the cabbage that took conventional fertilizer” and there was no change in taste. Many field tests have shown that urine is a good fertilizer for cereals, leafy vegetables, and fruits. Another study reported growth of cabbages was as good as with synthetic fertilizer. The same results were found for beans.

Urine is a good source of nitrogen and can replace the use of nitrogen fertilizers.

Is Sodium an Issue

Plants have a range of sensitivity to sodium but at high enough concentrations it is toxic to all plants. Beets are very tolerant of sodium and even high levels of urine (800 kg N per ha) produced higher yields. Carrots on the other hand are very sensitive to sodium and yield peaked at 50 kg N per ha.

Sodium should not be an issue provided it is diluted.

Is Ammonia Lost to Air?

Some people say it is not worth using urine in the garden because the urea quickly turns to ammonia which then evaporates into air. I think they believe this because you can smell the ammonia in urine, but the claim is not really true.

Urea reacts with water to produce an ammonium ion which is water soluble and can be used by plants. Some of this will turn into ammonia but even it is soluble in water. Ammonium is also converted fairly quickly to nitrite and then to nitrate by bacteria in the soil.

Diluting urine will keep more of the nitrogen in solution. Applying it to soil and watering it in will also help since ammonia released deeper in soil is less likely to escape into the air before microbes or plants use it.

Some of the nitrogen in urine will be lost, but most will remain in the soil.

Sweet Smelling Urine

If you don’t like the smell of urine, change it, while at the same time preserving the nitrogen.

Fermenting urine changes the odor and lowers the pH so that less nitrogen is converted to ammonia. Take your urine, add in some lactic acid bacterial inoculum (LAB) from sauerkraut juice and ferment it in a closed vessel for a month. Pickled pee might just become the next garden craze!

Find out more about LAB here.

Is Urine Sterile?

With certain illnesses it is not sterile, and without illness it is only sterile until it enters the urethra, at which point it gets contaminated. It also picks up microbes quickly once it exits the body. Contrary to popular belief it is not sterile.

Can Human Urine Transmit Diseases?

Urine can contain pathogens and you could potentially get sick from them. The major source for pathogens is from fecal contamination that occurs during the collection process. Provided you collect urine without contamination, it is rarely a problem.

Also consider that most gardeners use urine from their household and they are already in contact with the people carrying any diseases.

Can Urine Burn Plants?

All fertilizers, including human urine, should be used in moderation. Just as using too much chemical fertilizer can burn plants, using too much urine can harm plants by causing nutrient burn. To decrease this risk, urine should be applied to the soil at the base of the plant instead of directly on the foliage. Dilution solves burning problems.

Aging and Diluting Urine

From gardening information on the internet:

“Fresh urine will burn plants, aged is better.”

“Aged urine will burn plants, urine should be used fresh.”

How can both be right? Why does no one give a scientific reason for their suggestion?

Burning Plants

Dilution Rates

The internet suggests a wide range of dilution rations from no dilution to a 1:100 dilution rate.

Urine is 0.4% nitrogen, or 4,000 ppm. A good but safe level for nitrogen fertilizer is 100 ppm, so a 1:40 dilution ratio would produce a standard fertilizer solution and be safe even if applied on plants.

An even easier way is to just pour the undiluted urine over the ground and water it in. If you sprinkle a bit here and there, you don’t even have to water it in.

Aging changes the molecular form of nitrogen, but not the total amount, so aging does not affect dilution.

Pathogens

The real concern with urine are the pathogens. How does dilution and aging affect them?

Pathogens were tested using three different dilution ratios, 1:0, 1:1 and 1:3 (urine:water) as well as four temperatures 4, 14, 24 and 34 °C. Aging urine increases the ammonia level and when it gets high enough it kills pathogens. Storage of urine below 20 °C did not reduce pathogens effectively. Dilution decreases the ammonia concentration therefore it is best to store urine undiluted and above 20 °C. When stored this way for 6 months it is safe for unrestricted use.

Best Aging and Diluting Rates

I suspect most gardeners don’t want to store urine too long and if you are using your families urine you don’t need to store it for pathogens. Use it fresh and dilute to 1:40.

If you are concerned about pathogens, store it as suggested above.

What About Drugs in Urine?

Most drugs in urine have not been analyzed but there is some work done on antibiotics. The concern with these are toxicity and more importantly their ability to promote the develop of antibiotic resistant bacteria.

A study from the University of Michigan found that “recycled, aged human urine can be used as a fertilizer with low risk of transferring antibiotic-resistant DNA to the environment”, provided it was stored for 12 to 16 months. During storage, ammonia levels increase, lowering acidity and killing most bacteria and disrupting their DNA.

A study looking at veterinary antibiotics found that they degrade during composting and have half-lives from 5 to 462 days depending on the animal and the drug. The study also looked at antibiotic concentrations in vegetables grown on land fertilized with such manure. In most cases the level of antibiotics was below the limits of quantification (LOQ). “Highest sulfamethazine concentration (27.34 µg kg-1) occurred in lettuce harvested in one certified organic farm”.

Several organizations have established acceptable daily intake (ADI) values for some of the veterinary pharmaceuticals. Most of these ADI values are less than 10 µg/kg body weight per day which for an average person (50-75 kg) is equivalent to 500-750 µg per day. The maximum concentration of antibiotics in vegetable produce in the above study was less than 30 µg/kg wet weight. An average person would need to consume 17-25 kg of produce every day to reach the ADI safe limit. These antibiotic are not a major health risk.

Antibiotics are only partially digested and absorbed by the human body. Approximately 30%–90% are excreted through urine and feces within 8 to 24 hrs.

Another study looked at male urine collected at a university building in Beijing. Results showed that the urine contained 18 out of the 30 antibiotics tested. In fresh urine “the detected values, sulfonamides (2 antibiotics), tetracyclines (4 antibiotics), and fluoroquinolones (12 antibiotics) had a concentration range of 0.25–2.94, 0.94–41.2, and 0.06–163.16 ng/mL, respectively”. Storage of the urine for 30 days resulted in a significant decrease of antibiotics.

When urine containing carbamazepine and ibuprofen was applied to ryegrass, only carbamazepine was detected in the plants and soil after 3 months. Ibuprofen was not found in either the soil or the plant.

Antibiotics, and probably most drugs, will end up in urine. The amounts are relatively small and would pose no harm to plants. Antibiotics are absorbed in by crops in very small amounts. Even if you don’t use urine on your vegetables, you are already eating some animal antibiotics in your purchased produce. Organic produce might even have higher values than non-organic since these farmers relay more heavily on manure for fertilizer.

The risk to the environment for creating antibiotic resistant bugs is real. The solution is to reduce their use. Storage of urine for longer periods of time, or composting it does reduce the amount of antibiotics in it.

Urine on the Compost Pile

Should you put urine on the compost pile?

If you need some extra nitrogen then it will speed up the composting process otherwise there is no point in composting urine. It is already composted!

The reason you compost is to break large organic matter into smaller molecules, but urine is already mostly small molecules.

When Not to Use Pee

If you are taking medication, especially antibiotics, it is probably better not to use your urine. If you are sick with something like a urinary tract infection it is best not to put the urine on a vegetable garden, but it is fine to use on ornamentals.

How to Use Urine in the Garden

Use it straight in the garden and water it in, or dilute it 1:40 and use that directly either in the garden or on potted plants.

If you are concerned about drugs or pathogens, use it on ornamental plants and keep it out of the vegetable garden, but the reality is that it won’t cause any problems in the vegetable garden.

The concerns people have about urine are unfounded, except the real concern about producing microbes that are resistant to antibiotics.