Nutrients

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 can occur on a plant.

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:

Vegetative Stage

N P K

3:1:2

Flowering Stage

N P K

1:1:2

Final Flowering Stage

N P K

0:1:2

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

Micro Nutrients

Silica

Silica can increase stem diameter and boost chlorophyll production.

Magnesium

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

Calcium

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

Boron

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

Deficiencies

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

The most common deficiencies that I have come across are Magnesium and Calcium. There are liquid nutrient solutions (e.g. CalMag) that provide both. This should be added to the soil before planting if possible. Alternatively, one can use organic additions (e.g Dolomite Lime) but note that some sources will change the pH of the medium.

Using too many nutrients can create a nutrient burn on the leaves, primarily on the apex

Nutrient lockout

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

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.

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. 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 lensing through droplets 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.

Liquid fertilizer solutions can roughly be broken into two categories: those for the vegetative stage and those useful in flowering.

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