From what I’ve heard, New Zealanders are intimately familiar with the movie The World’s Fastest Indian. In it, Burt Munro (Anthony Hopkins) tells another character to pee on his lemon tree while he’s away, and claims Confucius said it’s the world’s best fertilizer. So, while this movie reignited the widespread idea of peeing on plants, is this really true—is urine good for plants?
Urine is generally acidic, high in nitrogen, and easily absorbed, making it a great fertilizer for most plants. However, the nitrogen from urea is usually too potent to use directly on plants. For best results, dilute 1 part urine to 10 parts water, or compost it. Urinating on plants on occasion won’t harm them.
Even though peeing on your plants can be an odd practice, it’s proven to be a great fertilizer. But what exactly does urine do to the soil, and can it kill plants in higher amounts? Let’s take a closer look (but not too close).
Why Urine is Good for Plants
Urine is 95% water, 2.5% urea, and 2.5% minerals including phosphorus and potassium. Salts, hormones, dissolved ions, compounds, and metabolites are also found in urine.
Urine typically offers an ideal pH for the vast majority of plants. Since plants prefer a pH of 5.5-7.0, and urine ranges between 4.5-7.8 (depending on one’s diet), there’s a lot of overlap in pH. However, in times when urine is too acidic or alkaline, soil amendments can be used.
Maintaining a slightly acidic soil pH of 5.5-7.0 is important for plants because the acidity helps dissolve the nutrient solids in the soil, making them accessible to the plant’s finer roots.
Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils.Donald Bickelhaupt, SUNY College of Environmental Science and Forestry
If you find that the urine you’re using is too acidic for plants (below 5.5), you can add some alkaline amendments such as wood ash, charcoal, or lime. If the urine is too alkaline (above 7.0), add some acidic amendments such as coffee grounds, sand, or peat moss. However, urine is generally more acidic than it is alkaline.
To be safe, for those of you who are more serious about regularly urinating directly on your plants, consider testing your urine with pH strips first. Also, depending on the amount of urine you’re adding, it may be a good idea to check the pH of the compost and soil to see if it’s getting too acidic.
While the pH of urine is typically fine for plants, the problem occurs with the excessive levels of nitrogen building up in the soil.
High Amounts of Nitrogen
Urine has 2.5% urea, which contains high amounts of nitrogen—the primary nutrient required by most plants. Plants use nitrogen largely to grow leaves and roots and absorb nutrients. This is why most fertilizing products display an NPK value, or percentage of nitrogen (N), phosphorus (P), and potassium (K).
[Nitrogen] is involved in various critical processes, such as growth, leaf area-expansion and biomass-yield production…Insufficient amount of N available to plants can hinder the growth and development.BioMed Central
Some plants, such as citrus and avocado trees, are heavy feeders and require double the nitrogen to phosphorus and potassium (an NPK ratio of 2:1:1). For example, fertilizers with an NPK of 6-3-3 works well for these plants.
However, urea has a much higher ratio of nitrogen than most fertilizers, with an NPK of 11:2:4. This is about 2-5x the potency of the preferred amount of nitrogen for most plants.
What is Urea?
Both urea and urine are different. In humans, urea is a nitrogen-containing waste substance that the kidneys clear from the blood and excrete into the urine. Human urine consists of water, urea, inorganic salts, creatinine, ammonia, and pigmented products.Divya Jacob, Pharm. D., Medicinenet.com
Over time, the nitrogen from the urea builds up in the soil. And when plants are exposed to high levels of nitrogen in the soil, their roots are chemically burned. This leads to issues such as yellowing leaves or dying plants. An overabundance of nitrogen is also common with chemical fertilizers.
As a result, diluting urine before applying it to your plant’s soil is essential.
As a liquid, urine is easily dispersed through the soil and absorbed by the plant’s finer roots. Compared to solids, liquids don’t need to be first dissolved in the soil. However, liquids that are potent with nutrients (such as urine) should be diluted to ensure the plant doesn’t get overwhelmed.
Is Human Urine Good for Plants?
Human urine is good for plants as long as it’s low in sodium and diluted. Sodium levels in urine largely depend on diet. With the Standard American Diet, excess sodium, preservatives, and medications are often present and can pass through urine, all of which are often harmful to plants.
Additionally, diets too high in protein can cause excess nitrogen levels in urine, potentially damaging the plant.
Is Dog Urine Good for Plants?
Dog urine is good for plants as long as it’s not a daily occurrence. If your dogs regularly pee on the same plants, the plant can become overloaded with nutrients and start to die. Consider training your dogs to go elsewhere, or water the plant more often to dilute the nutrient concentration in the soil.
I don’t know about you, but when we take our dogs out to the yard, they usually pee in the same spots. Because of this, the potent nitrogen is simply too strong for the grass and chemically burns its roots. As a result, the grass turns yellow and dies.
It makes our yard look like Swiss cheese.
This also applies to larger plants. For example, we have a certain shrub in the backyard that our two cattle dogs ALWAYS peed on. After about a week of them urinating on the shrub, its leaves turned from a deep green to a bright yellow.
However, after heavily watering the shrub to dilute and leach the existing urine in the soil, and training our dogs to not pee on it, the deep green color returned in another couple of weeks.
Normally, you don’t need to worry about your dogs urinating on most plants, but if it gets excessive, increase how often you water the plant or consider putting deterrents such as small fences or cayenne powder around the plants.
Can Too Much Urine Kill Plants?
We’ve already covered that too much urine can discolor leaves and kill grass, but it can kill the average plant?
Undiluted urine can chemically burn a plant’s roots and kill it, especially if its soil is dry. Additionally, any medications or diets that are high in sodium can pass in urine and negatively impact the plant. However, urine is unlikely to kill plants in small amounts, or after dilution or composting.
The first signs of a plant dying from excessive nutrients, such as those found in urine, are yellowing leaves. If you see the leaves yellowing and are fairly certain it’s from the urine, then pause or lower the volume of urine you’re using.
Additionally, if your plant currently has dry soil and is going through drought stress, urine will become even more concentrated in the soil and be directly absorbed by the plant.
How to Use Urine to Fertilize Plants
Use urine to fertilize your plants by diluting 1 part urine to 10 parts water, or by composting it. You can compost urine by adding it to your compost pile, getting a composting toilet, or urinating on a hay bale. When composting urine, make sure to balance the nitrogen with carbon such as hay, leaves, or sawdust.
Since diluting is fairly self-explanatory, let’s explore more about how to compost urine.
When saving or composting urine, one of the biggest problems is that ammonia starts to build up, and it starts to STINK. This can even negatively impact ammonia-sensitive livestock such as goats.
Fortunately, composting does a great job at containing the smell, ammonia, and harmful bacteria.
However, to properly compost, you’ll need to balance out the urea’s nitrogen with carbon. This is commonly referred to as the carbon-nitrogen ratio.
The ideal C/N ratio for composting is generally considered to be around 30:1, or 30 parts carbon for each part nitrogen by weight.Cornell University
While nitrogen is extremely useful for plants, its potency poses a problem. Luckily, carbon-based materials such as hay, leaves, bark, wood chips, or sawdust, are great at absorbing and suppressing ammonia, nitrogen, and contaminants.
So, by adding 30 times the amount of carbon to the urine, you’ll help prevent issues such as smell from developing. Keep in mind that 95% of urine is water, so 30 times might be an overestimate. Also, turn the compost pile as needed.
If you’re diluting the urine instead, make sure to apply it fairly quickly to prevent it from smelling.
However, if you’re still planning on urinating directly on the plants, start with small volumes in low doses. If the plant’s leaves start turning yellow or dropping, stop the application and heavily water the tree’s soil to dilute the remaining concentration of nutrients further.
How Often To Fertilize Plants With Urine
You can fertilize plants with urine daily as long as it’s diluted or composted. Generally, pastures with livestock require 30-60 days rest from manure and urine to recover. For this reason, avoid using undiluted urine regularly on plants. For larger amounts of urine, consider diluting or composting it first.
Since grass in pastures easily becomes overloaded with nutrients from manure and urine, livestock stewards typically provide that section of land around 30-60 days of rest before coming back to it (source). However, undiluted urine won’t negatively impact larger plants such as trees in small volumes.
There’s some truth that urine is “liquid gold” for the garden. Nitrogen, phosphorus, potassium, and other valuable nutrients and minerals are incredibly beneficial for plants. The only downside is that plants are generally unable to use the high concentration of nutrients in urine.
Overall, if your plant is occasionally exposed (pun intended) to urine, whether it’s from you or your dogs, it won’t kill the tree. However, if you’re intending to do a permaculture-like approach, and you’d like to recycle as many nutrients as possible for your garden, process the urine first by a 1:10 dilution or compost.
If you’re interested to see how an Australian gardener processes urine on his permaculture farm, check out this video by Happen Films. It’s just a quick look at their setup, but it definitely sparks some ideas (spoiler: they use the hay bale method). I’ve linked the specific time in the URL (5:54), so it should take you to the right spot in the video in case you’d want to virtually tour their farm for any other ideas.