How to correctly read fertilizer labels

Plants, just like people, need a balanced and healthy diet to develop. Newcomers to the world of cannabis growing sometimes feel a little lost in the food section, especially when reading fertilizer labels. But nothing is further from the truth: interpreting the nutritional information on all these products is a simple and quite useful task. We tell you everything you need to know about 5×10 grow tent and fertilizer bags so that they are no longer a headache.

We are paying more and more attention to product labels: saturated fats, kilocalories, proteins… and all kinds of nutritional values that give us a lot of information about our diet. When it comes to our cultivation of cannabis, we should do the same, as the diet of the plants is one of the most important factors for the success of the plantation. Thanks to the extra nutrients we bring to the crop, cannabis is able to resist diseases and pests and grow more vigorously to give us a good harvest at the end of flowering.

The fact is that fertilizers are also very cumbersome for newcomers, who are afraid of making mistakes with the amounts, combinations or type of nutrients. All these beginner’s fears can be quickly overcome by familiarising ourselves with fertiliser labels, which contain all the information we need. Even if we are not used to that kind of nomenclature, ratios and percentages, the labels are very easy to read, much more so than the labels on food in a supermarket.

Types of fertilizers and how they work

The function of fertilizers is to provide the plant with the necessary nutrients through the substrate, and to a lesser extent, from the leaves. Marijuana plants take oxygen, hydrogen and carbon from water and the atmosphere. However, they cannot develop without certain chemical elements found in the soil. When we plant cannabis in a good compost, the soil usually satisfies all these nutritional needs of the plant. But usually the substrate does not have enough chemicals to meet that demand on its own; so we turn to outside inputs to help us give the plant the extra nutrition it needs.

These are the fertilizers, an auxiliary food with which we must have an eye and calculate well the quantities and varieties according to the needs of the plant and the characteristics of the substrate. We can find fertilizers for cannabis in different formats and sizes, although the most common is to use fertilizers, liquid (which are quickly absorbed) or solid (dry fertilizers that take a little longer to work). We can also distinguish between complete nutrients, PK boosters, organic stimulators or organic fertilizers, also known as background fertilizers.

The most common fertilizers are those that include in the same product the macro-elements NPK (nitrogen, phosphorus and potassium), which are considered the three most complete nutrients for cannabis cultivation. In addition, these fertilizers may include secondary nutrients (such as calcium or magnesium) and trace elements (iron or zinc). Everything in its proper proportions to be applied in the vegetative phase or flowering, although there are also fertilizers designed to feed our plantation throughout the crop.

The information on the labels

The fertilizer packages are usually followed by the acronyms of the nutrients and some numbers. Generally, for cannabis we will look for NPK fertilizers, i.e. containing nitrogen (N), phosphorus (P) and potassium (K). This nomenclature also indicates an order, which is usually followed by three numbers, something like 30-10-10 or 2-3-4; they are the proportions that the fertilizer contains of each element, the first example would come to inform us that for every 100 kilos of fertilizers, we have 30 of nitrogen, 10 of phosphorus and 10 of potassium. In the second example, it could be that there is 20% nitrogen, 30% phosphorus and 40% potassium.

This means that in reality these numbers are indicative, so that you know that there is a superior ratio of one nutrient to another; they are not therefore exact percentages. In cannabis cultivation, an NPK fertilizer is used followed by a 4/2/3, (where nitrogen is higher) during the vegetative stage, i.e. when the plant is growing. In contrast, a 2/3/4 sequence, where there is more phosphorus and potassium than nitrogen, will be useful for flowering, when the plant develops buds. Remember that these are indicative references, so if you are going to change the brand of fertilizer it is important to check the label to see what exact quantities of each nutrient it has and what specifications the manufacturer makes on the product.

As far as dosage is concerned, it is also important to keep an eye on the label. The manufacturer usually recommends a maximum dosage, which can be used as a benchmark for feeding our cannabis plants. It is always advisable to start with a low dose and increase it every week until the maximum level referred to on the label is reached. After this maximum, the amount should be gradually reduced until the product is no longer used completely a few weeks after the harvest. Making a calendar with the doses will always be useful, although nothing like observing the appearance of the plant to perceive if it suffers from deficiencies or excesses of nutrients.

You may have noticed that the percentages on the label numbers do not add up to 100%. The rest are inert materials that help to disperse the nutrients. However, other nutritional microelements and their sources, such as iron and magnesium, also appear in the breakdown of the label.

The information on the label can also give us conservation advice, such as keeping it in the fridge once opened if you want to keep it for a few months.

Hopefully this mini-guide will have given you some relief if you were dizzy with the numbers and letters on the fertilizer containers. This is a simplified language for growers to quickly know what kind of nutrients and proportions the product offers.