Human urine, sometimes called “liquid gold,” is a highly effective and easily accessible source of nutrients for plant growth. This organic material contains significant concentrations of the three macronutrients that form the basis of most commercial fertilizers: nitrogen (N), phosphorus (P), and potassium (K). The approximate NPK ratio of human urine is often reported to be around 11:1:2.5, making it especially rich in nitrogen, which promotes leafy green growth. Utilizing this resource is a sustainable practice that closes the nutrient loop, but it requires a mandatory step for safe use in the garden. This powerful liquid must be diluted with water before application to prevent immediate harm to plants and long-term soil issues.
Understanding the Need for Dilution
Dilution is necessary due to the high concentration of soluble salts in urine, which can severely damage plant tissues. Undiluted urine causes “fertilizer burn” because its high concentration of nitrogen compounds, primarily urea, converts into highly alkaline ammonia when broken down in the soil. This ammonia can chemically scorch leaves and roots.
The excessive salt content creates an osmotic imbalance, drawing water out of the plant roots instead of allowing absorption. This desiccation causes visible damage, such as browning, wilting, or scorching of the foliage. Repeated application of highly concentrated urine also leads to a buildup of inorganic salts, causing soil salinization. This inhibits the plant’s ability to absorb water, which is detrimental to long-term soil health.
Essential Dilution Ratios and Guidelines
The most commonly recommended safe ratio for applying urine to mature plants is between 1 part urine to 5 parts water (1:5) and 1 part urine to 10 parts water (1:10). This range ensures the nitrogen is sufficiently dispersed to be safely utilized by the root system.
Heavy-feeding crops that demand high nitrogen, such as corn, squash, brassicas, and leafy greens, can tolerate a dilution closer to 1:5. General garden beds, including most established vegetables and ornamental plants, thrive best with the more conservative 1:8 or 1:10 dilution. Always err on the side of greater dilution if a plant’s sensitivity is unknown.
New seedlings, young transplants, and potted plants require the greatest caution, often needing a dilution ratio of 1:15 to 1:20 or more. Their tender roots and the restricted soil volume in containers make them highly susceptible to salt damage and root shock. Increase the dilution ratio during periods of drought or high heat, as dry soil conditions increase the immediate risk of fertilizer burn.
Safe Collection, Storage, and Application
Proper collection and short-term storage are essential. Urine should be collected in a clearly labeled, non-corrosive container with a sealable lid to minimize nutrient loss and manage odor. Fresh urine contains urea, which quickly breaks down into ammonia gas, leading to a strong odor and loss of valuable nitrogen.
To retain nitrogen and control the ammonia smell during short-term storage, some gardeners add a small amount of white vinegar to the container. Another common practice is “aging,” where urine is stored in a sealed container for one to six months. This storage naturally raises the pH and sanitizes the liquid, making it safer for use, though dilution remains necessary.
When applying the diluted fertilizer, direct the stream to the soil around the base of the plant, ensuring the mixture does not contact the leaves or stems. Applying it as a soil drench ensures the nutrients reach the root zone and prevents foliar burn. If the soil is dry, water the area thoroughly with plain water immediately after application to distribute nutrients and flush remaining salts further into the soil.
A frequency of once every two to four weeks is generally appropriate during the active growing season. Stop application when crops enter their reproductive stage (when fruit or flowers begin to form) to prioritize nutrient needs for those processes.
Hygiene and Safety Precautions
For safety and hygiene, observe the following precautions:
- Do not apply urine, even diluted, to crops that are eaten raw or grow close to the ground, such as radishes, carrots, or low-lying berries.
- The World Health Organization recommends a waiting period of at least one month between the final application and the harvest of any raw-eaten food crops.
- Individuals taking strong medications, such as antibiotics or chemotherapy drugs, should avoid using their urine in the garden due to the potential for pharmaceutical residues.