These initials represent the percentage of nitrogen, phosphorus and potassium in the fertilizers that are used to feed cannabis plants. They are the most important nutrients for the plants to grow healthy and yield good results, although the amount of each of these nutrients will depend on the stage of the crop and the strain. Being aware of this is crucial for the proper development of our marijuana plant.
If you've ever purchased chemicals for the cultivation and care of your cannabis plants you may have noticed a small detail that stands out in bags or cans containing fertilizers and that for first-time growers is not well known. Usually, all of these containers feature the initials NPK, accompanied by three numbers (or just the numbers alone), similar to this example: 'NPK 12+ 8+11'.
The figures vary from one product to another, but they are always placed in the same order. This is one of the most important equations to treat our plants: the amount of nitrogen (N), phosphorus (P) and potassium (K) contained in the product we are using. In some places, like Australia, the letter S is often added, referring to sulfur.
Those numbers always refer to percentages, normally approximate. Each of them depends on the characteristics of the nutrient, among other factors. Nitrogen, phosphorus and potassium are called 'macronutrients' because they are the most important compared to other secondary ones which are also integrated into fertilizers, such as iron, zinc, manganese, calcium or copper.
Understanding the appropriate level of these macronutrients needed at each phase of culture is essential, since it will influence if your plants grow strong and healthy or, on the contrary, end up in bad shape, generating a reduced crop or even dying. Providing too little or too much fertilizer can be extremely harmful to crops and can cause counterproductive results.
Generally, during vegetative growth (between germination and flowering) a nutrient solution high in nitrogen and low in phosphorus is usually recommended. However, during flowering high levels of phosphorus and low of nitrogen are needed (it could be illustrated as follows: 5-25-9). However, the calculation should not worry anyone, as each fertilizer product is usually presented with a label indicating for which stage of cultivation it is most suitable.
The level of nitrogen needed depends on the product weight and stands as one of the most important elements to feed the cannabis plant. The lack of this substance is usually one of the most common nutritional problems; it causes lower leaves to turn pale green and even yellow. However, excess is more common and harmful, since it makes the plant more vulnerable to disease.
Fertilizers rich in this element are mainly used during the growing period of the plant, due to its crucial role in photosynthesis and growth. During flowering, its level will be lower, unlike in the other two periods. This component is used for the plant to grow faster and to create chlorophyll and have a nice green colour.
Meanwhile, cannabis plants make use of phosphorus during all the stages of its growth, although with higher levels during germination and especially during flowering. It often contributes to a better production of the buds, to root development and to obtaining good oil afterwards. It is also necessary for the respiration of grass and for the storage and transfer of energy between all its parts.
For its part, potassium plays an important role in protein production, flower quality and photosynthesis. Its presence is therefore appropriate at a high level during the earliest stage of vegetative growth.
Among other things, it strengthens the immune system of marijuana against insects and diseases, helps in the process of opening and closing the pores of the leaves and is essential for protein synthesis. It is also involved in the activation of more than 60 vital enzymes that regulate the plant’s growth rates.
At the moment, there is no general consensus on what should be the exact and appropriate percentage of nutrients at each period since, legally, verifications on marijuana are restricted on a large scale. This is the reason why many of the blends simply mimic compounds that function correctly in vegetable crops while others depend on what the manufacturer considers to be most beneficial.
For example, Flora Bloom (by General Hydroponics, which can be purchased at La Mota), for the flowering phase, contains 0-5-4, which means it has about 0% nitrogen, 5% of phosphorus and 4% potassium. Flora Gro, in the meanwhile, contains 3-1-7; i.e. about 3% nitrogen, 1% phosphorus and 7% potassium.
However, it is advised to prepare the plant just before flowering by nourishing it for a week with the same amount of each nutrient. On the other hand, experts recommend not mixing different products from different manufacturers, since they may not work well together.
It is also necessary to distinguish between taking care of the plant indoors and outdoors. Outdoor growers must take into account that average soil does not provide enough food for marijuana, so it is necessary to create a richer soil. This can be achieved, for example, by using worm humus to provide more nitrogen and phosphorus or wood ash for potassium.
The amount of potassium must be properly levelled, since it may increase plant stress in drought conditions. Beyond this, it is an alkali metal which reacts aggressively with water and oxidizes on contact with air, so it is often added to fertilizers in the form of various compounds.
If grown in pots, in most cases indoors to take advantage of a suitable climate, the only plant that absorbs the fertilizer is marijuana and not any other one nearby, as it usually occurs outdoors. Those who opt for this choice often use organic fertilizers that are particularly well adapted to autoflowering plants. This is very important at the end of the growth phase. In addition, if grown in pots, it is recommended that the product used contains a NPK with high nitrogen content.
In both cases, the pH level of the soil and earth must be controlled, because it is always more compromised when the plant is outdoors (by external agents that may affect it). In general, it should be between 6 and 7 and should always aspire to be as close as possible to 6.5. In the soil it is appropriate to apply low doses of nitrogen.
Also, the type of fertilizer and nutrients needed depends on whether the crop is grown on soil or in hydroponics. In case it is on the ground, it will contain many components that the plant will absorb during its growth cycle. When the soil runs out of these components, they will need to be replaced by fertilizers to maintain a strong growth and so that benefits are greater.
If marijuana is taken care of by means of hydroponics cultivation, specific fertilizers will be needed for this modality. Usually these often include those secondary nutrients or micronutrients found on soil.
As we can see, taking care of marijuana’s nutrients is essential to obtain the desired culture results and for these to be optimal.. It is best to be guided by experts, take a look at the options that stores offer and opt for the one that seems most appropriate according to each grower’s experience.