Urine as a Fertilizer

How do I spend my Saturday mornings you ask? Answer: scanning the peer reviewed literature for articles about using human urine as a nitrogen source in the garden, i.e. taking a leak in the watering can. As we’re currently hosting some excellent classes at our house taught by Darren Butler, a big proponent of what he calls “pee-pee-ponics,” I thought I’d take a look at the science of urine use.

Urine offers a free and readily available (at least after a night of beer drinking) alternative to organic nitrogen fertilizers such as blood meal. We’ve got a perpetual nitrogen deficiency in our vegetable beds and I hate buying industrial ag sourced items like blood meal. Urine is a great alternative.

To use urine in the garden you’ve got to dilute it with water, at least ten to one. Straight urine will burn your plants. Thankfully we don’t worry about our sauerkraut taking on a urine flavor:

Use of Human Urine Fertilizer in Cultivation of Cabbage (Brassica oleracea)––Impacts on Chemical, Microbial, and Flavor Quality by Surendra K. Pradhan, Anne-Marja Nerg, Annalena Sjöblom, Jarmo K. Holopainen and Helvi Heinonen-Tanski

Human urine was used as a fertilizer in cabbage cultivation and compared with industrial fertilizer and nonfertilizer treatments. Urine achieved equal fertilizer value to industrial fertilizer when both were used at a dose of 180 kg N/ha. Growth, biomass, and levels of chloride were slightly higher in urine-fertilized cabbage than with industrial-fertilized cabbage but clearly differed from nonfertilized. Insect damage was lower in urine-fertilized than in industrial-fertilized plots but more extensive than in nonfertilized plots. Microbiological quality of urine-fertilized cabbage and sauerkraut made from the cabbage was similar to that in the other fertilized cabbages. Furthermore, the level of glucosinolates and the taste of sauerkrauts were similar in cabbages from all three fertilization treatments. Our results show that human urine could be used as a fertilizer for cabbage and does not pose any significant hygienic threats or leave any distinctive flavor in food products.

As the study above noted, too much nitrogen (from any source) can cause pest outbreaks. And we do need to be judicious in our urine application in alkaline soils such as here in Los Angeles as urine has a high pH:

From Human urine – Chemical composition and fertilizer use efficiency by H. Kirchmann and S. Pettersson:

Stored human urine had pH values of 8.9 and was composed of eight main ionic species (> 0.1 meq L–1), the cations Na, K, NH4, Ca and the anions, Cl, SO4, PO4 and HCO3. Nitrogen was mainly (> 90%) present as ammoniacal N, with ammonium bicarbonate being the dominant compound. Urea and urate decomposed during storage. Heavy metal concentrations in urine samples were low compared with other organic fertilizers, but copper, mercury, nickel and zinc were 10–500 times higher in urine than in precipitation and surface waters. In a pot experiment with15N labelled human urine, higher gaseous losses and lower crop uptake (barley) of urine N than of labelled ammonium nitrate were found. Phosphorus present in urine was utilized at a higher rate than soluble phosphate, showing that urine P is at least as available to crops as soluble P fertilizers.

With some common sense urine application (i.e. not too much), it clearly makes a good fertilizer:

Stored Human Urine Supplemented with Wood Ash as Fertilizer in Tomato (Solanum lycopersicum) Cultivation and Its Impacts on Fruit Yield and Quality by Surendra K. Pradhan, Jarmo K. Holopainen and Helvi Heinonen-Tanski:

This study evaluates the use of human urine and wood ash as fertilizers for tomato cultivation in a greenhouse. Tomatoes were cultivated in pots and treated with 135 kg of N/ha applied as mineral fertilizer, urine + ash, urine only, and control (no fertilization). The urine fertilized plants produced equal amounts of tomato fruits as mineral fertilized plants and 4.2 times more fruits than nonfertilized plants. The levels of lycopene were similar in tomato fruits from all fertilization treatments, but the amount of soluble sugars was lower and Cl− was higher in urine + ash fertilized tomato fruits. The β-carotene content was greater and the NO3− content was lower in urine fertilized tomato fruits. No enteric indicator microorganisms were detected in any tomato fruits. The results suggest that urine with/without wood ash can be used as a substitute for mineral fertilizer to increase the yields of tomato without posing any microbial or chemical risks.

So go forth and pee (and dilute!). You can also, of course, just pee on the compost pile.

Many thanks to the always useful Google Scholar, one of my favorite gardening resources.

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18 Comments

  1. I love it!
    I have always peed on my compost pile, and from this year have been diluting and using it in the garden as well. It has worked well for me if the plant’s other conditions are met as well. For example, my buckwheat is growing gangbusters, but since the rice crop’s water was too cold, and they are pretty stunted.

  2. My dad does this, though I’m not sure how much he dilutes it by. Unfortunately, it makes our front yard smell like a Santa Monica alleyway which is Not Pleasant. Does diluting it 10 to 1 reduce the horrible smell, or is this just how it goes?

    • Yes, diluting will not only help with odor but should be done to prevent damage to plants and roots due to too high concentration. Also, the urine should be “fresh”. No more than 24 hours old. There really shouldn’t be in any odor if you are using fresh diluted urine.

  3. So does natural mesquite charcoal ash count as wood ash? And if so, what proportions of urine, ash, and water would our tomatoes and orange tree enjoy?

    A little off topic, but can you compost charcoal ash? I’m just throwing it away now because I’ve been afraid to add it to the compost bin.

  4. christianhertzog–our western soils are too alkaline to use wood ash as a soil ammendment.

    mjaui–using urine immediately should help with the smell and dilution is essential.

    Penny–you can reduce urine burn by hosing down after dog incidents.

  5. Did anyone write a chapter on how to induce a guy to do this? Exbf and another friend think I am nuts. They don’t doubt it might work, but either “forget” or say “no.” One guy (friend) takes testosterone shots and an experimental, legal drug for the army. I wonder if his urine should even be put on the garden or lawn. Will an excess of testosterone hurt either?

  6. I’ve had the dood doing this for me for as long as we’ve been working on improving our soil and the compost piles :) And when our cat Pancho insists on “amending” with a pee spot, we just hose it to dilute. Works pretty well. Pancho’s specialties are fruit trees…

  7. I cannot believe the timing of this post as just this morning Matt was telling me that he wanted to look into using urine as fertilizer. He read about it somewhere and wanted to learn more. Seriously, impecable timing. Thanks for the source articles too. I look forward to reading even more!

  8. Interesting, I didn’t know it had to be diluted first. I always have my husband pee on the compost pile, which I know is something a little different, but that’s good to know about the dilution for plants!

  9. The other benefit of using urine as a fertilizer is fresh water savings in the home and lower utility bills (toilets are huge water users). Instead of peeing in the toilet, I pee in a 1/2 gallon milk jug (put the cap on!). When the jug is full, I walk out in the garden and sprinkle it in one one of several compost bins. I’ve been doing this for years, and the water savings is considerable. In addition, the urine in the compost bins helps to keep down the fruit fly population.

  10. Chuck–
    One thing that would help is a soil test–UMass has a cheap one. That way you’ll know if you need to add nitrogen. Another thing to look for–too much green leafy growth which can lead to pest problems–this is a sign of too much nitrogen. Also, if you live where there are alkaline soils (such as the southwest) you have to watch out for signs of salt burn (urine is high in salts).

  11. I have heard that peeing into hay bales is a great practice. Pee and hay make a great match due to their high carbon and high nitrogen contents. The bale then breaks down and can be composted. I have heard of people doing this at festival/concert venues.

    Do you think it is possible to do the same thing with a pile of leaves. One could have a 55 gal trash can filled with leaves and pee into it, and as the leaves break down you can add more. I guess peeing into the compost pile would do the same thing. Any thoughts? I was also thinking that if you had a drip system you could elevate your 1:10 ratio of pee to water in a 5 gallon bucket hook up a hose to the bottom of the bucket and gravity feed your pee water into the drip system. You could also add it to your grey water system by pouring the pee water into a sink.

  12. This might be a silly question but it’s one I’ve wondered about. I would like to use urine as fertilizer on our garden, but should we start applying the diluted pee now when the garden is fallow and mulched? Will the nitrogen still be available to the plants in the spring? Or should I wait until spring when the plants are planted and growing? I live in Kentucky- so we got several months until growing season again.

    BTW, finally bought your newest book through our local bookshop. Along with your first book, I’m using it as part of a “home ec” curriculum for a bunch of homeschool kids- really great stuff!

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