Best Cannabis Nutrients

Best Cannabis Nutrients
Nutrients for marijuana plants

A plant can create its own food from water, CO2 and sunlight. But to optimally grow and flower, the plant needs additional fertilizers. Outside, in nature, plants get their nutrients from the soil, which is rich in minerals, and dead plants and animals provide the necessary fertilizers. If you’re growing indoors, you’ll need to provide your plants with nutrients yourself. If you’re growing outside, it’s smart to give your plants some additional nutrients.

Every bag of soil or bottle of plant feed will label the N-P-K ratio. This is the ratio between nitrogen, phosphor, and potassium. These are the macronutrients, the most important nutrients. Additionally, there are some micronutrients such as iron, copper, and zinc.

In this course I’ll teach you about the different types of nutrients and their purpose. Furthermore, the symptoms of a deficit or surplus will be discussed.

Nowadays, it’s no longer necessary to make nutrients yourself, because you can buy great products that are developed specially for weed plants.

Of course I’ll show you the feed I use and I’ll give you some tips about other brands.


Carbon (C), hydrogen (H) and oxygen (O)

These are the three most essential building blocks to a plant. A plant can, in combination with sunlight, convert these elements to sugars it uses to grow.

In the open air these elements are present, but indoors you need to water your plants yourself and you have to provide them with fresh air.

Especially the CO2 is very scarce in the air and will be absorbed by the plants in a growing room. A fan that blows fresh air into the room already suffices.

There are also systems available to increase the amount of CO2 in the air. This is usually done by burning propane or adding carbonic to the growing room.

Growing weed this way is very expensive and is reserved for very experienced growers.

That’s why I won’t elaborate on this right now. This is possibly a nice subject for a masterclass.

nitrogen for marijuana
Nitrogen for marijuana

Nitrogen (N)

It is an important component of chlorophyll, the substance that give the leaves and stems their green color.

Nitrogen promotes the growth of the plant and serves the production of stems, leaves and the initial production of the buds.

Much nitrogen is therefore needed during the growing phase. A good growing feed therefore has a high nitrogen content.

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A lack of nitrogen will lead to yellowing leaves and a slower growth. The discoloration starts at the bottom of the plant and slowly moves upwards.

The bottom leaves are the oldest and the plant sacrifices these leaves to obtain their nitrogen for new growth.

The leaves turn very dark green during a nitrogen surplus. The growth and maturation of the plant slows down and the plants look limp with many watery stems and leaves.

This makes the plant vulnerable to diseases, fungi and pests.

Phosphor for marijuana
Phosphor for marijuana

Phosphor (P)

It plays an important role in the respiration and energy supply of the plant.

It promotes the development of the roots of young plants and the flowering of adult plants.

Phosphor is very important to your plants during the entire cultivation.

A lack of phosphor causes the leaves the shrivel and turn dark green, purple and brown. The stems turn red or purple and the side roots develop very poorly.

A phosphor shortage often occurs during a wet spring or with plants that are watered too much.

The soil has a hard time making phosphor available to the plant in this case.

The leaves remain small and curl up in case of a surplus of phosphor. The buds of a mature plant could ripen too quickly.

It also prevents the absorption of other nutrients, such as zinc and iron. If you’re using fertilizers that are specially developed for weed plants, the ratio will always be correct.

Potassium for marijuana
Potassium for marijuana

Potassium (K)

It is very important for the production and transportation of sugars inside the plant.

Potassium gives the plant firmness, makes it resistant against fungi and diseases and helps with the formation of the roots.

It’s also very important for the production and growth of the buds. Potassium is therefore needed during the entire cultivation, but the plants could use some additional potassium to create thick, hard buds.

A lack of potassium leads to discoloration and withering of the edges of the leaves.

Fewer buds will be created and the buds will be weak and of poor quality. The plant also becomes more sensitive to fungi and diseases.

A surplus of potassium causes the leaves to burn, starting at the tips.

The buds will contain more water, resulting in a lower weight once they dry. It also hinders the absorption of magnesium and boron.

Calcium for marijuana
Calcium for marijuana

Calcium (Ca)

It plays an important role in the production of cells and is therefore especially needed during the growing phase.

It also promotes the absorption of nutrients and is used to improve the structure of the soil and increase the pH value.

A calcium shortage mainly affects the big leaves at the top of the plant. The leaves show yellow spots, encircled by a brown edge.

They look a bit like rust spots. The growth slows down and the production decreases.

A surplus of calcium can cause the pH value to become too high and can lower the absorption of other nutrients.

This can have serious consequences, but a calcium surplus almost never happens.

Magnesium for marijuana
Magnesium for marijuana

Magnesium (Mg)

It is a necessary element for photosynthesis and various other chemical reactions inside the plant. The plant should therefore always possess sufficient magnesium.

A shortage of magnesium will create yellow spots on the leaves, although the veins of the leaves remain green.

This usually occurs in older leaves, but a serious deficiency can also affect younger leaves.

Magnesium is inadequately absorbed if the pH value is too low, thereby creating shortages.

A surplus of magnesium almost never happens. The possible harmful effects are therefore not really known.

Trace elements for marijuana
Trace elements for marijuana

Trace elements

These elements are, if they’re needed, necessary to a plant in only in very small quantities. These tiny quantities are however vital to the plant.

If you use feed by a good brand, you’ll never have a shortage of trace elements. Everything your weed plants need is provided in the feed, so you don’t have to worry about a thing.

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Iron (Fe)

It is Important for the production of chlorophyll and the respiration of the plant.

A lack of iron leads to small yellow spots in young shoots and leaves, although the veins remain green.

It is sometimes confused with a magnesium deficiency, because it shows similar symptoms. A surplus in iron is laid down in phosphate in a form that can’t be absorbed by the plant.

Manganese (Mn)

It plays a role in cell division, photosynthesis and metabolism.

A lack of manganese causes discoloured yellow spots in the buds and between the veins of older leaves, which won’t develop properly either.

The taste of the buds can differ because of a manganese deficiency. A surplus of manganese is toxic to the plant.

Boron (B)

This element plays a role in the transportation of nutrients inside the plant.

A lack of boron can be recognized by the black spots on young leaves and the death of the growth point.

A lack of boron is not common, but is usually the result of a surplus of nitrogen or potassium.

Molybdenum (Mo): Plays a role in the nitrogen supply. A lack of molybdenum leads to discoloration of the edge of the leaves.

A lack of molybdenum really only occurs in acidic soils, and the best medicine is increasing the pH (with lime). You could spray your plants with seaweed fertilizer dissolved in water.

Silicon (Si)

It creates firm plants and increases the resistance against fungi. A lack of silicon can be recognized by a lack of growth and limp, sad plants.


Necessary element for the production of proteins, hormones and vitamins.

A lack of sulphur looks a lot like a lack of nitrogen, because both cause yellowing of the bottom leaves. The stems can also turn purple and the growth slows down.

Other trace elements, for which no scientific proof has yet been found regarding their function, are found inside plants.

Examples of this are cobalt, sodium, chloride, nickel, chromium, selenium and iodine. A surplus of these elements usually has a harmful and/or toxic effect on the plant.

As you can see, there’s usually not just one deficiency and one solution.

You might think a plant doesn’t get enough nitrogen, because the bottom leaves are turning yellow.

But is that because of a lack of nitrogen in the soil, because the plant can’t absorb it yet or because of a lack of another element?

That’s why I advise you once again to use known feed that’s specially developed for weed plants.

It usually comes with a feeding schedule and you could ask the seller for advice in case you have problems.

You can of course also post your questions to other students and growing experts., so check out our forum.

Read how to make a feed solution in the course How do I make a feed solution.