Beginners guide to home-made fertilizer

A small plant sprouting from soil

Gardening on a budget? Keen to choose natural methods? Concerned about the environment? Prefer not to purchase fertilizers advertised for growing cannabis? There are many good reasons for making your own fertilizer. This post has been brought to you by the letters N, P, and K!

Cannabis plants, like all members of the plant kingdom, need nutrients to thrive. In fact, it’s important to remember that the soil is what is being fertilized, not the plants themselves. Soil contains a complex miniature ecosystem of microbes that act like the plants’ digestive system, breaking down nutrients into a form that can be absorbed by the roots and give the plant the building blocks it needs to grow healthily. The primary nutrients required by cannabis plants are nitrogen, phosphorus, and potassium.

N, P, K – as easy as A, B, C

These three vital nutrients are known by initials for short. N stands for nitrogen, P stands for phosphorus, and K stands for potassium. Wait, K stands for potassium? Are we high? No, K is short for kalium, the Neo-Latin name for potassium. On commercial fertilizer packaging, the three numbers that appear refer to the ratio of N, P, and K, always in that order. The ratio is important because cannabis plants need different levels of fertilizers depending on what stage of their life cycle they are in.

What fertilizers should be used when in the cannabis plant life cycle?

During vegetation, cannabis plants need high levels of nitrogen, which is used for developing healthy and plentiful leaves and stems, and medium levels of phosphorus, which is necessary for good root systems. This feeding program should be continued for the first couple of weeks of flowering, to allow for the ‘stretching’ period, when plants will need plentiful nitrogen. Once flowering is properly underway, levels of nitrogen should be kept low, and levels of phosphorus should be increased, since phosphorus also enables plentiful budding and fruiting. Potassium is needed at all stages, and especially high levels are needed during flowering – preferably, it should be twice the level of nitrogen. Generally, phosphorus tends to increase the number of buds, and potassium increases their bulk and weight.

Where can these nutrients be found?

For beginner gardeners, obviously the easiest solution is to buy a couple of bottles of cannabis fertilizer, one for vegetation and one for flowering. However, there are various reasons that this might not be possible or desirable. So what are the alternatives for those who want to try making their own fertilizer? They can be surprisingly close at hand, in the form of kitchen waste and even human urine! Below we have compiled a list of common substances and what nutrients they contain. Solid substances work best when cut into small pieces and dug into moist soil either prior to planting seedlings or whilst repotting into larger containers. Liquids can be diluted with water and used as liquid fertilizer.

A graphic of the different fertilisers that can be used

1. Coffee grounds

Coffee grounds are rich in nitrogen and also contain significant levels of potassium and phosphorus, so they are one of the easiest ways to fertilize your plants during vegetation.

2. Banana skins

Contain plenty of phosphorus and potassium, so useful for the flowering period. They also contain calcium and other minerals that are beneficial to cannabis plants.

3. Bean water and beans

Also known as aqua farba, the liquid that chickpeas, white beans, lentils, black beans, broad beans, and many other tinned pulses come in is a source of potassium, as are the beans themselves.

4. Spinach and other vegetable water

Steaming or boiling spinach (and many other vegetables) will leach out some of the nutrients into the water. Once the water has cooled, it can be used as part of a regular watering schedule to add potassium, calcium and iron.

5. Urine

Human urine, when fresh, is a perfectly fine and non-toxic source of nitrogen, phosphorus, and potassium. Nitrogen is by far the largest useful component, so this is another good liquid fertilizer for during vegetation. Urine should also be diluted considerably before being added to the soil – it should never be directly applied to the plants!

Another great way of providing natural and organic fertilizers to cannabis plants is by making organic compost tea. This is slightly more complicated than digging kitchen waste into the soil, but will provide larger batches of food.

What substrates can these natural fertilizers be used with?

When grown in coco coir, rockwool, or other inert substrates, all of the nutrients must be provided by the gardener. This is a tricky mix to get right, and there are plenty of commercially available fertilizers that ensure plants will get everything they need. If hydroponic watering systems are used, it is also preferable to stick to the specialist fertilizers that are designed for them. Attempting to use homemade fertilizers in hydroponic systems inevitably leads to more problems than it solves, as the tubes will clog and unwanted, unpleasant bacteria will swiftly take over your feed tank. Soil, however, is far more forgiving and lends itself to being fed with organic matter.  It’s also vital to keep the soil properly hydrated.

We hope you have enjoyed these basic beginner tips for making organic fertilizer. Do you have your own to share? Let us know in the comments!

  • Disclaimer:
    Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.


9 thoughts on “Beginners guide to home-made fertilizer”

  1. If you want plenty of nitrogen put in the soil olive leaves , if you want calcium put ashes in top of the soil but the ashes must be clean , only from trees , no paper or other chemicals burned 😄

    1. Hey Axaios- thanks for the tips about Olive leaves. Do they need to be broken down? Or just mixed into the soil? With Gratitude, 1st time planter.

  2. Nettles do make a very good liquid fertilizer; Firmly pack a drum with nettles, pulled out of the ground with the roots, and add water to cover them. Then be prepared for an almighty stench after a couple of weeks! Start adding the liquid in small proportions to your watering can when the stems have rotted. You may add more water to the drum as the rotting continues. It is advisable to keep a lid on the container and try not to get the liquid on your hands as the stink seems to stay in your skin forever. Good luck!

    1. Scarlet Palmer - Sensi Seeds

      Hi Birdman,

      Great, thank you so much for the info!

      With best wishes,


  3. Come diceva Andy un macerato di ortiche è ottimo, aiuta a prevenire attacchi dei parassiti e funghi, in più aiuta molto la fotosintesi nelle foglie…. Da provare…. Ciao….

    [from google translate, for the non-Italian speakers (including me): “As Andy said, a maceration of nettles is excellent, helps prevent pests and fungi, plus it helps photosynthesis in the leaves …. To try…. Hello…” – Scarlet]

    1. Scarlet Palmer - Sensi Seeds

      Hi Andy,

      Thanks for the info! This is surely one of the cheapest ways of making your own fertilizer also 🙂

      With best wishes,


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    Scarlet Palmer

    A lifelong interest in altered states has led Scarlet through many career experiences, including artist, writer, environmental activist, Muppeteer, and professional cannabis dealer. Scarlet believes that spreading factual information about drugs empowers people to make informed and sensible decisions on drug use, reducing harm caused by ignorance.
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