Plant Food: A look at Micro- and Macronutrient

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Plant Food: A look at Micro- and Macronutrient

Learn the ins and outs of cannabis nutrition, to ensure the signs you cannabis gives you never go unnoticed.

When it comes to growing cannabis like a pro, knowing your nutrients like the back of your own hand is an essential skill. It will help you read the individual needs of a cannabis plant, and ensure they are never left wanting. This is something that comes with practice, and the first step is to learn about the nutrients themselves, so that you know what they do, and what it looks like when your cannabis isn’t getting enough.

So let’s delve right in and take a look at the macro- and micronutrients you cannabis yearns for.


There are three main macronutrients your cannabis plants needs in abundance, at regular intervals:

Nitrogen (N)

Nitrogen is essential for proper growth. It accounts for 40-50% of dry matter in cannabis plant cells and is involved in photosynthesis, growth, efficient root absorption, and the creation of amino acids, nucleic acids, and proteins.

Nitrogen is especially important during the vegetative stage of growth, when a cannabis plant is putting all of its energy into fleshing out and growing large. It is used up very rapidly, making nitrogen deficiency the most commonly seen nutrient deficiency in any grow room.

A symptom of nitrogen deficiency is yellowing leaves. This tends to start in lower, older leaves, and gradually works its way up the plant. This is due to the plant removing what little nitrogen it has left from older leaves to give to younger, more vulnerable growth; it is known as “symptom creep”. The result is leaf death and slowed growth.

Too much nitrogen has the opposite effect, accelerating growth beyond safe limits. It causes the plant to stretch, resulting in undermined structural integrity. An overabundance of nitrogen can also slow down and prevent flower growth, as well as inhibit the absorption of calcium.

Phosphorus (P)

The role of phosphorus within cannabis is to aid photosynthesis, help flowers bloom, and encourage healthy root development. It is also essential for the efficient uptake of nitrogen, and the creation of nucleic acid. Because of its bloom boosting ability, higher levels of phosphorus are often used during the flowering stage of cannabis growth.

A deficiency in phosphorus causes a general slowdown in efficiency of the plant. As it is also vital for the uptake of nitrogen, phosphorus deficiency can manifest itself as a nitrogen deficiency – so be careful.

Too much phosphorus inhibits the uptake of iron and zinc.

Potassium (K)

Potassium, the last primary macronutrient, is used for carbohydrate and protein creation, immune system response, and for photosynthesis. It is also involved in many enzyme reactions, as well as responsible for keeping the “plumbing” of a cannabis plant in order – ensuring liquids moving in an efficient manner.

Potassium is instrumental in the absorption of silica.

A potassium deficiency often results in leaf edges turning brown/yellow as well as potentially causing the leaf to curl over. After this, yellowing spots begin to appear on the leaf’s interior, both on top and on the underside. Symptoms tend to show on lower leaves first. Prolonged deficiency can also cause signs of wilt.

Too much potassium can cause problems with the absorption of calcium and magnesium.


The secondary macronutrients are often present in soil, and only used in small amounts. However, they are still essential, and may need supplementation at some point. They will likely need full supplementation in a hydro system.

Sulphur (S)

Sulphur, apart from smelling terrible, is used by cannabis for enzyme and amino acid production.

A sulphur deficiency causes leaf yellowing, much in the same way a nitrogen deficiency does. However, unlike a nitrogen deficiency, a sulphur deficiency starts in the upper leaves, not the lower.

An overabundance of sulphur tends to be well tolerated by cannabis. However, it can prevent molybdenum (a beneficial bacteria) from doing its job.

Calcium (Ca)

Calcium is mainly used for the creation cell walls, and plays an important part in some enzyme reactions. It is also thought to help with the creation of growing points – especially in root tips.

If the cannabis isn’t getting enough calcium, it can result in new leaves appearing with dead cells. This often causes leaves to curl under.

When too much calcium is present, iron uptake can be inhibited.

Magnesium (Mg)

Magnesium’s main function is to create chlorophyll, but it is also used for certain enzyme reactions. As such, magnesium plays a vital role in leaf health, and in the maintenance of leaf veins.

A magnesium deficiency causes yellowing in between leaf veins. It appears as a symptom creep, first affecting older leaves before moving to new ones. It can also cause premature aging.

An overdose of magnesium can inhibit the uptake of calcium.


Micronutrients play an important part in healthy cannabis growth, but are only used in extremely small amounts - and we mean really small. If you are growing in soil, then many of them may already be present and unlikely require supplementation. None-the-less, learning what they do, and what their deficiencies look like, can help you make sure you cannabis never misses out – just in case.

Boron (B)

Boron is used in the creation of new root tips, as well as stabilising cell walls.

A deficiency of boron can cause leaf tips to curl and then eventually die. It can also cause cannabis plants to grow shorter than their usual potential.

Too much boron can cause leaves to become glossy.

Iron (Fe)

Iron is needed for proper chlorophyll production. It is also necessary for some enzyme reactions to take place.

Iron deficiency causes new leaf growth to start out bleached. It also causes current leaves to yellow in between the veins, which eventually results in leaf death.

An abundance of iron in the soil will compete with zinc and copper for absorption, possibly locking them out.

Zinc (Zn)

Zinc is used to facilitate enzyme reactions.

A zinc deficiency can result in yellowing between the veins of new leaves and cause purplish dead cell spots. This tends to start on lower leaves, working its way up in a symptom creep.

Having too much zinc present can cause iron uptake to be inhibited.

Manganese (Mn)

Manganese is required for the creation of chlorophyll and certain enzyme reactions.

A manganese deficiency causes yellowing in between leaf veins. This starts at the top of the plant and works its way down.

An overdose of manganese can cause cell death in leaves, and can also lead to a deficiency in iron.

Copper (Cu)

Last but not least is copper. Copper is used in the creation of proteins and is involved in the strengthening of stalks, stems and branches.

A copper deficiency can cause leaves to darken while causing edges to turn yellow. It can also give leaves a glossy look, and prevent bud from growing efficiently.

Copper toxicity is extremely rare, but should it happen, it can cause quick cell death.

It is quite a list! But having it handy can help you discern what your cannabis is telling you, and help you develop an innate knowledge of what it needs. You don’t need to have all this memorised in order to successfully grow cannabis, but just keep it in the back of your mind, and have it ready to hand should you notice you current feeding schedule is causing signs of deficiency/toxicity. In time, you will instinctively know what is needed, and be able to adjust your feeding to suit!