" Blog da Horta Biológica: Nettle Slurry: Benefits and How to Make It

Nettle Slurry: Benefits and How to Make It

Nettle is an excellent plant, not just for gastronomy and health but also for taking care of other plants on farming and gardening. In this post we talk about the benefits of nettle slurry and, at the end, you find our video about how to make nettle slurry step-by-step.

What Is Nettle Slurry?

Nettle slurry is a concentrated liquid obtained by maceration of this plant. This is a biological process that takes several days and results from the decomposition of organic waste. Nettle slurry benefits both plants and soil, and can be used for both spraying and watering.


Nettle slurry is a great ally in organic farming because it is a totally natural product and is very versatile in its use. It is an excellent fertilizer, an effective stimulant for plant growth, it has a protective action against diseases, a repellent effect against pests, and is also a compost activator.


Nettle, among other properties, has a high content of nitrogen, sulfur, iron, phosphorus, silicon, magnesium, potassium, vitamins, and micronutrients. Sometimes, land has these in limited quantities. Because nettle is so rich in properties, it can be used as a liquid fertilizer, enriching the soil and developing plant growth.


Nettle benefits soil and plant growth in several ways. 

  • It absorbs nitrogen in the soil, supplying it to plants. Nitrogen is the element that plants need the most, being essential for their growth.
  • It facilitates photosynthesis due to the carbon dioxide produced by its bacteria. 
  • The immersion of the seeds in nettle slurry before cultivation, stimulates the growth and resilience of the plants. 

Protection Against Diseases

By providing the soil with the missing nutrients, it stimulates the defense mechanisms of the plants, strengthening them and making them more resistant to diseases, especially those caused by fungi, such as mildew, powdery mildew, and mold.

Pest Repellent

In addition to protecting against diseases, nettle has bactericidal and antiseptic properties. In nettle naturally occurs formic acid, which is produced by the plant for the purpose of self-defense. Due to its abilities as a natural insecticide it is very effective against aphids, mites, the red spider, the white fly, and other unwanted creatures in the garden.


Because it has a large amount of nitrogen, nettle favours the activity of microorganisms and is an excellent activator of the composting process. The bacteria present in the liquid stimulate fermentation and accelerate the decomposition of organic waste.

How To Make Nettle Slurry?

Required Material

  • 2 Plastic or wood containers with 15L capacity (do not use metal)*
  • Rubber gloves
  • Scissors 
  • 1 Kg of fresh nettles, preferably without flower*
  • 10L of rain or distilled water*
  • Filtering cloth
  • Funnel
  • 2 recipients for storage (water bottles will do)


  • Use long-sleeved shirts and thick clothing to avoid skin irritation. 
  • The preparation should be done outdoors due to the smell it will cause in the following days. 

*Do not use metal because nettles are rich in acids such as acetic, butyric, and formic. The reaction between acids and metal can release toxic substances.

*Preferably without flower because although nettles can be harvested practically all year round, before flowering they are less fibrous and decompose more easily. Blossomed nettles will also do the job but they will take loner to decompose and will also result in more fibrous tissues, with less use of the plants. 

*Rain or distilled water because the water that is used to make nettle slurry must not contain chlorine. This is very important, as chlorine kills most of the bacteria responsible for fermentation.

Preparation Method

  1. Cut the nettles and place them in the container, add the water, and stir to mix well.
  2. Cover the container and store it in a sheltered place without direct sunlight. The temperature must be between 18ºC and 25ºC.
  3. Stir every day to release the accumulated gases and to better involve the plants in the water. Cover the container again after stirring. The fermentation process takes time and will depend on the air temperature. Heat accelerates the process, cold delays. Generally, after a week, the fermentation process should already be underway. We know that it is fermenting if there's foam on top of the water.
  4. Keep stirring every day until the foam disappears. This process releases a very strong smell, so it must be done outdoors. When foam disappears, the fermentation process ends and the slurry is ready to be filtered. It may take up to two weeks to complete. This slurry that we made for this post was made during the month of March, in which we had very hot days and very cold days. Our nettle slurry took 18 days to be ready to use.
  5. Use a cloth to filter the slurry. It might be necessary to make more than one filtration. The liquid should be as clean and free of residues as possible, so that it does not go bad and so it has a longer shelf life.
  6. Place the remains of the plant in the compost pile.


Store the liquid immediately by pouring it, with the help of a funnel, into a container with a lid. Store the container in a cool, dark place. Under these conditions, nettle slurry may last more than a year. It is also very important to label the container in order to remember the date the slurry was made.

How To Use Nettle Slurry?

Nettle slurry is highly concentrated, so it must be diluted. See the percentage dilution in table below.

Many vegetables and other plants appreciate nettle slurry. Examples of this are cabbages, tomatoes cucurbitaceae, fruit trees, roses, and other flowers. 

Onions and legumes will be less likely to enjoy the application of nettle slurry. However, when in doubt, it is always a good idea to experiment in a small part of the garden and see how the plants react to watering and spraying with nettle slurry.

All of this process takes a lot of time and work but it is worth it! There's nothing like knowing that we are taking care of ourselves, our food, and our land in a totally natural way.

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