Nutrients can broadly be categorized by micro or macro and in terms of their mobility; either mobile or immobile. Mobile nutrients are those that the plant can move around to where they are most needed while immobile nutrients cannot be relocated. This mobility of the nutrient affects where symptoms of deficiency (or excess) can occur on a plant. Mobile nutrient deficiencies will appear on older leaves first and vice versa.

Buying fertilizer

Most fertilizers on the market come in 2 categories; general nutrients for the vegetative stage and flowering (or bloom) nutrients for the flowering stage of growth. Vegetative nutrients contain large amounts of Nitrogen and flowering nutrients contain mostly Potassium and Phosphorus. There are also solutions that provide micronutrients, sugars, and acids to boost growth even further.

An increasingly discussed distinction between fertilizers/additives is the difference between organic and synthetic. This mostly refers to the method of extraction, origin, and form of the nutrients included in the fertilizer. For example, amino acids can be synthesized chemically or they can be provided organically via fish meal. Synthetically derived nutrients tend to be in salt forms. Both organic and synthetic nutrients can be used together, and the decision of whether to use the former or the latter is often decided by an individual's growing arrangement.

Common Fertilizer Ingredients

Macro Nutrients

Macronutrients are those nutrients that Cannabis requires in large amounts, the three main nutrients are Nitrogen, Phosphorus, and Potassium (often written as NPK). They typically come from the soil and are crucial throughout the plant's lifespan, although in differing ratios.

Vegetating plants require more Nitrogen and less Phosphorus and Potassium, while flowering plants demand much less Nitrogen and much more Phosphorus and Potassium during the flowering stage. A rough guide NPK ratio:

NPK ratio by life stage
Stage N P K
Vegetative stage 3 1 2
Flowering stage 1 1 2
Final Flowering Stage 0 1 2

It's worth noting that the NPK ratio stated on a bottle of fertilizer does not reveal anything about the absolute amount of Nitrogen, for example, in the product.


Required for the production of most plant cells as well as chlorophyll, used in photosynthesis.


Essential for the flowering period, Phosphorus strengthens the plant and is used for root development.


Required for root development. Potassium also regulates the opening and closing of stomata for gas exchange.

Cannabis also obtains Oxygen, Carbon, and Hydrogen from water and air.

Micro Nutrients

Micronutrients are the elements that are needed in much smaller quantities than macronutrients, however, this does not make them any less important.


Silicon dioxide or "Silica" can increase stem diameter and boost chlorophyll production.[1] Found in Diatomaceous earth.


A mobile nutrient required for the creation of chlorophyll in a plant, a requirement of Photosynthesis.


An immobile nutrient that is required for the creation of strong cell walls.


Similar to calcium, boron is required for strong cell walls.


Copper is used in photosynthesis by helping metabolize proteins and carbohydrates.


Iron supports the function of chloroplasts.






Chloride refers to Cl-, not to be confused with the toxic form chlorine CI. Essential for the proper function of stomata.


Acids chelate other nutrients making them more water-soluble and thus more available to the plant. Humic acid is commonly used to increase the number of nutrients that the cultivar can absorb.

Amino Acids

Humic and fulvic acids


Enzymes help speed up the breakdown of nutrients and carbohydrates. Adding enzymes can significantly speed up flowering time.

A group of enzymes, known as Diastase, can be found in malted barley[2].




A genus of beneficial bacteria with 266 named species.


Mycorrhizal Fungi

Some fungi can live symbiotically with the plant's root system, they consume some glucose created by the plant while increasing nutrient uptake. Some soil mixes come with mycorrhizae already added, you can buy it separately and combine it with your medium, or it can be added to the medium in the hole where a plant will be transplanted.

Sugars and Carbohydrates


A key component of insect exoskeletons, shells of crustaceans, fungi, and components of other invertebrates. In plants, it benefits pest and disease resistance as well as being a strong chelator and increasing the production of secondary metabolites.

Molasses and oligosaccharides

Plant Growth Regulators (PGRs)

PGRs are a group of hormones that are used to increase the density of buds and reduce plant height. There are organic PGRs but there are also a number of synthetic PGRs that are known to be carcinogenic and toxic to the liver. PGRs are generally not recommended for use on cannabis unless you know exactly what the PGRs are and how they were sourced.


A phytohormone found in Alfalfa that acts as a stimulant. It increases the rate of photosynthesis by increasing the production of chlorophyll, and assimilation of CO2. It also increases the rate of cell growth and reduces stress.


Chelation is the bonding of organic compounds with metal ions, for example, humic acid and iron. When chelated, the organic compound encapsulates the metal (an example of a micronutrient) forming a shield that protects it. This not only increases the solubility of the nutrient, and thus absorption in the plant, but it also prevents the metal from being lost through runoff or from oxidating before it reaches the plant. Chelators can even expand the bioavailability of nutrients beyond the typical pH required for absorption.

More on chelation at Maximum yield: Understanding Chelation in Plants and The Chelation Effect: Maximizing Plant Growth.

The sequence of nutrition

The biochemical sequence depicts the order in which nutrients are required by the plant and the interconnections between nutrients.

Nutrient antagonism

High concentrations of one nutrient can decrease the bioavailability of another, this is known as nutrient antagonism. For example, high Nitrogen will decrease the availability of Boron.


Most deficiencies present as a color change on the leaves, moving from the center outwards or from the edge of the leaf moving inwards. Deficiencies can appear on older leaves first or newer leaves first. Mobile nutrient (such as NPK) deficiencies will show on older leaves first as the plant moves nutrients to the younger leaves. Deficiencies will remain in leaves that have already finished growing even after it is remedied in fresher leaves. This means you must be patient in remedying mobile deficiencies

Nutrients can be added to the growing medium before planting if possible, to avoid deficiency.

Nutrient lockout

The availability of nutrients in soil at different pH

Nutrient lockout occurs when the pH is too high or too low for the plant to properly absorb nutrients. This leads to a deficit of necessary nutrients for growth and/or survival. A nutrient lockout can also occur when the grow medium accumulates too much salt or other nutrients.

More on ideal pH

Pre-mixing nutrients

If you intend to mix nutrients in water in large quantities and leave it to sit for a period of time one should consider the nutrients used and how they may change over time. When mixing organic nutrients in water they will respire aerobically for a period of time, until they run out of oxygen and then begin to respire anaerobically. This destroys some of the bacteria's capabilities and makes for a less effective feed. The water will begin to smell like a pond or an asshole when the bacteria begin to respire anaerobically which is a surefire way to tell. Synthetically derived nutrients may last longer in water but can also become less effective as some nutrients may combine to create less accessible forms of the nutrient for the plant.

Methods of Nutrient delivery

Via growing medium

The most simple method of nutrient delivery is by mixing with the water to be used for watering the cultivar. Take note that the growing medium will affect the stability of the pH in the plant's root zone. Organic soils provide more of a pH buffer than hydroponic systems because, in organic soil, there are other organisms that help regulate pH. Even though nutrients have been added to the growing medium they will not be bioavailable to the plant instantly. Other organisms, such as Mycorrhizal Fungi and Microbes, help in the process of breaking down nutrients so that they are useable by the cultivar.

Foliar Spray

Nutrients can be delivered to the plant when dissolved in water via a fine mist, this is the fastest route of administration. It has been postulated that the size of the droplets has an effect on the efficacy of foliar spray but some studies seem to contradict this[3]. If possible the spray should be applied to the underside of leaves as this is where most stomata reside. Lights should be turned off before foliar spraying to prevent the light from lensing through droplets and burning the leaf surface. Foliar spray should not be used to provide emergency nutrients to the plant.

Sources of nutrients

Nutrients can be provided to a cultivar via concentrated liquid solutions, dry amendments, organic materials, and even other organisms living in the growing medium.

If you are trying to provide NPK organically you can check the NPK values of most organic materials at


In the last two weeks before harvest, a plant should be fed water with no added nutrients/fertilizer. This is to ensure the cultivar is able to metabolize all nutrients it has absorbed from the soil.[4] This leads to a smoother smoke containing less damaging compounds. The color of the ash left by burning cannabis can indicate how much fertilizer is present and if the plant was flushed or not. White ash indicates low amounts of excess nutrients left over and black ash indicates high amounts or possibly no flushing period.