What Is NPK? [Fully Explained]

Perhaps you are new to cannabis cultivation, or maybe you’re struggling with macronutrient deficiencies. Perhaps overfertilization is what’s spoiling your marijuana? Whatever substrates you decide to grow with, plants require the right nutrients at the right time. If you’ve decided to start growing marijuana for the first time, trying to determine the best nutrients for your setup can be quite confusing.

There are various nutrient companies out there on the market, and each of them develops multiple types of nutrients for different purposes. There are two main life stages for marijuana plants; vegetative growth and the flowering stage – and each has different nutrient requirements.

NPK fertilizer is a complex fertilizer that is primarily composed of the three key nutrients required for healthy plant growth. NPK stands for nitrogen, phosphorus, and potassium, and these are the primary ingredients that are needed to grow strong, healthy, and budding marijuana plants. The agriculture industry relies heavily on the use of NPK fertilizer to ensure healthy crops and global food supply.

Why is NPK Important?

Not all types of plants require the same nutrients, and sometimes you can do more harm than good when you apply chemicals haphazardly. Applying a fertilizer that is high in nitrogen will cause some types of plants to put all their energy into producing foliage at the expense of flowers. But nitrogen is a necessary component for growing cannabis plants.

If you’ve ever bought chemicals for the cultivation and care of cannabis plants, you might have noticed a small detail that stands out in cans or bags that contain fertilizers and isn’t well-known to first-time growers. Typically, all of these containers feature the initials NPK, which is accompanied by three numbers. For example; NPK 12+8+11.

These numbers vary between products, but they’re always placed in the same order. It’s one of the most important equations when it comes to growing cannabis plants; the amount of nitrogen (N), phosphorus (P) and potassium (K) that is present in the fertilizer product that is being used. In some places, like Australia, often the letter S is added – referring to Sulfur.

Cannabis plants require nitrogen, phosphorus, and potassium throughout their lifecycle to grow. Each of these nutrients plays distinct yet equally vital roles in the development of the cannabis plant. Here’s a closer look at each:

  • Nitrogen: Although nitrogen is readily present in the atmosphere, most plants can’t absorb it from the air and instead need to absorb it from the soil through their roots. It’s especially important for photosynthesis and is usually a key player in the diet of a cannabis plant during the vegetative stage.
  • Phosphorous: Unlike nitrogen, it’s not easy to find phosphorus in its natural form in the environment, mainly because it’s highly reactive to other substances. Phosphorous is key for the development of strong roots. Cannabis plants that are flowering usually need extra phosphorus – this is reflected in the high concentration of phosphorus that is found in fertilizers designed for use during flowering.
  • Potassium: Like phosphorus and nitrogen, potassium helps to strengthen a plant’s metabolism and is necessary for both the plant’s production of vital proteins and photosynthesis. It’s also needed to help strengthen the plant’s immune system, which leaves it more resilient to infections, diseases, and pests.

Now, it’s important to point out that phosphorus, potassium, and nitrogen are important throughout the cannabis growth cycle, but the ratios in which the plants need nutrients will change depending on the part of the growth cycle that the plant is in. For instance; seedlings require different nutrients to those plants that are about to start flowering.

The Simple Guide to NPK Ratios for Marijuana

As we’ve already discussed, NPK nutrients cannot be applied in the same ratio throughout the whole cannabis life cycle. Furthermore, cannabis plants nutrient requirements differ significantly from strain to strain. I’m sure that you will agree that figuring out the correct ratios for plant dosage can be pretty complex.

Let’s simplify the cannabis plant feeding process for growers of all levels.

Vegetative Growth

Early on in the cannabis life-cycle, the nutrient requirements are minimal. In this case, less is definitely more. The majority of growers favor a high N feed. An NPK ratio of 3:1:1 is an excellent macronutrient feed during the growth phase for just about all cannabis strains. But, of course, there are certain strains that may respond better with a bit of tweaking.

It’s not just about nitrogen, but the N levels should always be significantly higher than phosphorus and potassium until bloom.


As the cannabis plant transitions into the flowering phase, the macronutrient requirements swing in the opposite direction. This means adjusting the NPK ratio. The recommended and very effective NPK formula for early to mid-bloom is 1-3-2, followed by 0-3-3 for late bloom.

Feeding: Heavy, Light, and Just Right

Soil growers only really need to water plants during the seedling stage. Usually, adding beneficial enzymes and microorganisms is enough. This helps the roots to develop and make the nutrients in the soil readily available. However, coco and hydro growers are advised to start by applying approximately 25%-strength feeds and work up from this base level.

Some strains, specifically indica strains, tend to respond better to higher doses of fertilizer, while sativas usually correspond to fewer nutrients. Hybrids and auto-flowering strains occupy the middle ground – some lead toward a preference for higher or lighter doses.

NPK Fertilizer Production

NPK fertilizer is available in gaseous, liquid, and granular form – which is the most common. There are many methods for producing granular NPK fertilizer. Individual components may be produced separately and then blended together in specific formulations to develop target nutrient ratios or grades. Or, all-in-one granules that contain the desired ratio in each granule might also be produced. Here are some of the most common approaches for producing granular NPK fertilizer:

  • Drum Granulation Systems
  • Spheronizer Granulation Systems
  • Pipe Reactor Granulation Systems
  • Mixer-Dryer Granulation (Incorporating a pug mill) Systems
  • Disc Pelletizing Systems
  • Prilling Systems

Nitrogen, Phosphorus, and Potassium Sources


Most fertilizers used to grow cannabis that are available commercially include NPK; nitrogen, phosphorus, and potassium sources. Usually, this is clearly displayed on the packaging of the product with numbers, as we showed above.

Homemade Fertilizers

Some growers opt to produce their own fertilizer mix. This is ideal for experienced growers who want to have more control over the nutrients that their plants get. However, it can be challenging for inexperienced cultivators.

In fact, if some ingredients used to make fertilizers are used incorrectly, there can be a negative reaction. This is why it’s very important to ensure that you know what you’re doing if you opt to go down this route. Producing homemade fertilizers also requires precise measuring to ensure that the mixture has the right concentration of NPK.

If you would like to make your own homemade fertilizer, here is a basic concoction that you can start with to get the plants all the basic nutrients that they require:

  • 4 parts cottonseed meal
  • 2 parts of wood ash
  • 2 parts phosphate
  • 1 part limestone
  • 1 part kelp meal

Final Thoughts on NPK and Cannabis

Using the best cannabis growing nutrients is only the beginning. However, it’s a very important part of the cultivation process. There are several other things that you need to consider for optimal nutrient intake. Firstly, you should check the pH levels of the water to prevent deficiencies. Furthermore, the type of fertilizer and nutrients that are needed depending on whether the crop is grown in soil or in hydroponics.

At the end of the day, it’s important to understand what type of nutrients are required and at what stage of the cannabis plant life-cycle. This can make a huge difference to the cultivation process and is essential for growing healthy plants.

Seeds and Soil
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