NPK Fertilizer Ratio for Weed

NPK fertilizer ratio for weed relates to the amount of Nitrogen, Phosphoprus and Potassium a marijuana plant needs for optimal growth.

Being a marijuana grower comes with great responsibility. Each stage of growth is equally important and the plants must be given necessary care so as to yield highly. One of the important aspects is giving your marijuana plants vital nutrients. Just like humans need proteins, vitamins and carbohydrates to maintain a perfect health, our marijuana plants will need Nitrogen, Phosphorus and Potassium. These are the main nutrients and could be referred to as macronutrients. When applied in the right ratios, we will have huge, healthy crops that will be pleasing to the eye and yield-wise. We are going to look at when and how these 3 nutrients should be applied.


As it goes, nitrogen is rated the most important nutrient in marijuana plants. It is vital for the good development of stem and leaves of the plant. This is mainly in the vegetative stage of our plants. It also contributes to the overall size of the plants. Formation of chlorophyll and amino acids is the work of nitrogen and comes in handy during photosynthesis.

Deficiency in nitrogen will lead to yellowing of leaves in your marijuana plants. Lower leaves also may fall and generally, the whole plant becomes pale.

Excess of nitrogen is not good for our plants. It will lead to rapid growth but the plants won’t have good flowering. This, in turn, would reduce the yield. Excess nitrogen is also a contributor of molds at a later stage. Therefore, it is prudent to use only the required amount.


Phosphorous is essential in high amounts especially in the flowering phase of the marijuana plants. Adequate phosphorous ensures big formation of buds. It also comes in handy in the transfer of energy formed during photosynthesis. Good seed formation is enhanced by phosphorous.

Phosphorous is highly volatile and hence it will not be found in its pure elemental form. It is because of this reason that you will find a measure of its oxides in fertilizers.

Cloning solutions have phosphorous since it helps in root formation in marijuana plants. When the plant transits from the vegetative to the flowering stage, phosphorous levels should be adjusted accordingly.


Potassium assists our marijuana plants in the synthesis and transportation of sugars. It is also essential for water and other nutrients absorption. Potassium also enhances good root systems and contributes to the overall robust growth of the plants. The immune system is greatly reinforced by the presence of potassium. This type of nutrient should be present moderately at all stages of growth of your plants.

Soil Tests

Soil tests play an important role in ensuring that we put the right amounts of nutrients in our plants. They show the current state of the soil, indicating how much of each major nutrient is required. These tests include pH level. Marijuana plants do well at a pH level of 6.5. It would be wise therefore to lower or increase the levels if they are fluctuating upwards or downwards.


Usually, there are no specific ratios that one should use when applying NPK fertilizer ratio to the plants. However, there is a standard formula that seeks to guide marijuana growers.

In the vegetative stage, we should have a ratio of 2-1-2 at the seedling level. During the early vegetative stage, it should be adjusted to 4-2-3. The advanced vegetative stage that transits to flowering should have a combination of 10-5-7.

In the flowering stage, we ought to have the following: In the cycle change over from the vegetative phase, we have a ratio of 7-7-7. During early flowering, it should be adjusted to 5-10-7. In the full flowering stage, we will have 6-15-10. Late flowering will be 4-10-7. As we can clearly see, the levels of nitrogen and phosphorous adjust accordingly but potassium tends to be constant.

Other nutrients, fondly referred to as micronutrients are used alongside NPK. They together ensure that plants are healthy and give good yields.


In the application of nutrients, one needs to adhere to the NPK fertilizer ratio and the plants will respond appropriately. Care should be taken so as not to under feed or overfeed the marijuana plants since the consequences of both are dire.