Nutrients for Cannabis Plants: A guide for beginners

Posted by Dave Tutko on

Four years ago a friend asked me if I wanted to buy any clones from him.  I told him that I suck at taking care of any type of plants and they would end up dead.  He told me anyone can grow cannabis.  After some thought, I decided to buy two clones from him, even though I had no clue what I was doing.   For a first grow, I did pretty good.  I sometimes think much of that has to do with beginners luck, as I had very little knowledge of nutrients.  This is an overview of the basic nutrients that any plant needs to survive. 

Like all living things, plants need food (nutrients) to live.   Nutrients are divided into three categories, primary nutrients or macronutrients, secondary  nutrients , and micronutrients.  Primary nutrients are just that, the main nutrients the plant needs to thrive.  The plant generally needs these in large quantities and at different stages in a plants life.  These nutrients are Nitrogen, Phosphorus, and Potassium.

Secondary nutrients are needed in smaller quantities by the plant, and these are Calcium, Magnesium, and Sulphur.

 Finally Micronutrients and these are required nutrients but on a very small scale.  These are Boron, Chlorine, Copper, Iron, Manganese, Molybdenum, Nickel, and finally Zinc.

Nutrients are also categorized as either mobile nutrients, or immobile nutrients. This is important to know, as it will help you in identifying any nutritional deficiencies that your plant could have.

Mobile Nutrients are just that they move throughout the plant where the new growth occurs.  Once the plant starts to uptake the nutrient, it moves it to the newer areas of the plant.  This is the reason mobile nutrient deficiencies will appear at the bottom of the plant first.  All of  your primary nutrients Nitrogen, Phosphorus and Potassium  are  mobile nutrients, the other two are Magnesium and Zinc.

Immobile Nutrients can’t be translocated or mobilized throughout the plant.  Therefore immobile nutrient deficiencies will appear at the top of the plant. The immobile nutrients are Calcium, Boron, Chlorine, Cobalt, Copper, Iron, Manganese, Molybdenum, Selenium, Silicon and Sulphur.  

The percentages of these are clearly labeled on plant food and fertilizer.  This is called the NPK ratio.  So if a product has a 5-5-5 on its label, that means the product is 5% Nitrogen, 5% Phosphorus and 5%Potassium. They are always listed in that order.  NPK nutrient requirements change during a plants growth.  For instance, during the vegetative stage of a plant (usually starting between weeks four and five) the plant will require more Nitrogen.



Nitrogen is most essential during the vegetative stage of the plants life. Nitrogen is a mobile nutrient, it is required for growing new leaves, the green color of the leave, photosynthesis   and even aids in defending the plant from pests.

First signs of a nitrogen deficiency is yellowing at the bottom of the plant, if the yellowing is ignored it will continue up the plant.  This is because it is a mobile nutrient.   Eventually the leaves will brown, curl and drop.  Severe nitrogen deficiencies could potentially cause decreased bud sites and reduce your yield.

Product recommendations for products high in Nitrogen include three Down To Earth products and they are Blood Meal, Feather Meal and Bat Guano.  ( I will put the NPK ratio of these products)


 Next we have phosphorous a mobile nutrient, it essential for root development and growth, it is critical during the flower stage. It’s important to cut down on the nitrogen and increase phosphorus and potassium.  Too much nitrogen in flower stage will result in poor bud structure, reduce potency, reduce yield and inferior buds.

   My plants are currently in the flower stage and I am using Roots Organics Uprising Bloom which has a NPK ratio of 3-6-4.   I also use Papas Perfect Poop at the beginning of flower and then again half way though flower.  Papas Perfect Poop has an NPK ratio of 5-10-2

 Phosphorous deficiency symptoms include bright red stems, leaves darken becoming gray, blue or even dark green, leaves turn purple or red.  The leaves even could look shiny. 

Finally we have Potassium also a mobile nutrient. It is important in assisting the plants metabolic functions, works with phosphorous it works to strengthen the root system. IT also provides resistance to drought and increases the consistency and strength of the plant tissues.  Also it is important during flowering because it increases the weight, density and volume of the buds.   I have with great success in my last few grows have used a product called Overdrive NPK 1-5-4, in the final few weeks of flower.

You can tell a potassium deficiency because the leaves turn yellow from the tips toward the center of the leaf, ending at the base of the leaf.  Stems are weak and also bend easy. 

The other two mobile nutrients are magnesium and zinc.  A Zinc deficiency will cause the leaves to yellow and stay green on the outside of the leaf.

You will often hear people talk about calcium and magnesium deficiencies and supplements or Cal-mag. Magnesium being a mobile will start showing at the bottom of the plant, the signs of this are the leaves becoming light green and may start developing brown spots.  Leaves eventually will turn all yellow.  Calcium being a mobile nutrient the new growth will appear unhealthy, and new leaves will develop brown spots that will never go away.

Most Cal-mag supplements also contain iron, the reasoning is if there is a deficiency in one it can trigger nutrient deficiencies of the others.  Some growers just use a Cal-mag supplement.  I have been using Stoned Dust as directed for my last grow and this one and the results have been great.  Stoned Dust is an organic soil additive made from rock dust, right here in Massachusetts.  

This is just a quick overview of basic nutrient information, there is so much more to learn and practice.  I want you to remember this, when you are checking your plants mobile nutrient deficiencies start on the bottom of the plant, and three of those nutrients are the most important ones, so it’s important to check daily. Knowing this should make it easier to troubleshoot potential problems with growing. Happy growing! 

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