How to use urine to fertilise plants

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Option 1: when watering plants

Urine needs to be diluted before use. Some plants like stronger concentrations than others. A dilution rate of 1:8 is good for general use, but 1:3 has been used on plants that really like nitrogen, such as corn, cabbages and rhubarb.

1:8 dilution means topping up the average 300ml pee with 2.4l water, making around 2.7l.

Work the diluted solution into the soil around the roots. This helps soil bacteria break down the urea (the nitrogen-containing part of urine) into a plant-useable form.

Option 2: directly to a compost heap

Urine can be added to a garden waste compost heap without dilution. This helps the woody parts (carbon) decompose more quickly.

Food scraps and green garden waste also add nitrogen to compost heaps, so don’t add too much urine to these types of compost heaps, or mix in carbon-rich matter such as straw, ash, cardboard or even sugar.

Tips

  • For tender plants, seedlings and containers that don’t drain into the ground, pee should be extra-diluted at 1:20-50. Urine can have a higher salt content than commercial fertilisers, and in pots this can build up over time.
  • Urine is potent! It contains 9.3g urea per litre, equalling a nitrogen content of around 4.3%. By comparison, blood meal is 12% nitrogen and cow manure is 0.6% nitrogen. In other words, urine is contains around 7 times the nitrogen as manure.
  • Don’t stop using your usual compost. This will provide essential organic matter which helps keeps soil micro-organisms healthy. Think of urine as a nutrient supplement – we still need to eat!
  • Think of feeding the soil, not feeding the plants. A healthy soil is great for healthy plants. Fertilising with urine before rain can be good as it helps the urine spread through the ground.
  • If you use a wood-burning stove, wood ash is a great source of potassium which can be used in combination with urine for an all-round fertiliser. Ash is also slightly alkaline which urine can help counteract.
  • Nitrogen washes out of the soil quicker than phosphorus or potassium. That means it’s best to apply it little by little over the growing season.
  • Undiluted urine is usually too strong and can damage plants – use this to your advantage to kill young weeds.
  • Avoid splashing leaves if you’re going to eat them!
  • A well-mulched soil can tolerate undiluted urine.