Fertilize the nutrients you need to get the most out of your cannabis.

How and when to fertilize your cannabis plants


Everything you need to know to best feed your cannabis seedlings, which are very sensitive to nutrients. Read this article to find out how and when to fertilize your cannabis seedlings while avoiding possible mistakes and severe burns.


  • What nutrients do cannabis plants need?

  • When to fertilize cannabis?

  • EC, pH and water temperature

  • How to recognize any fertilizer problems?

  • Chemical or organic fertilizers?

Nutrients needed by Cannabis

The nutrients that cannabis needs vary according to the stage of life it is in. Cannabis seedlings absorb all the nutrients from the seeds and absorb water from the leaves as their roots develop (this is why it is critically important to keep them in a warm and humid environment). It will not be necessary to start feeding the seedlings until they are about 3-4 weeks old, at which point 3-4 true leaves have grown and enter the vegetative growth phase.

Nutrienti necessari per cannabis NPK azoto fosforo potassio
Some growers choose to start their plants with a light 2: 1: 1 fertilizer (i.e., NPK ratio) early in the planting period until their seedlings begin to enter the vegetative growth period. Other growers, on the other hand, have seen good results by starting planting immediately with 4: 2: 3 fertilizer.

Midway through the vegetative phase (about 6 weeks after germination), we recommend that you actively increase your plants’ nutrients to help them form strong, healthy leaves. At this stage, most growers choose to fertilize their cannabis with a 10: 5: 7 fertilizer.

This high nitrogen content will help your plants produce dense green leaves and make many shoots bloom over time. At the end of the growing season, it is best to reduce the nitrogen content to prepare the plant for the transition to the flowering period. Most growers use 7: 7: 7 fertilizers during the last week of the growing season.

Flowering cannabis plants require less nitrogen and more potassium to encourage the growth of large resin flowers. In the first two weeks of flowering, most growers feed flowering plants with a 5: 7: 10 fertilizer. From now on, the usual practice is to maintain nutrients in all aspects and maintain the concentration of potassium higher and higher. Halfway through flowering, most growers will use a 6:10:15 nutrient solution.

Pianta di cannabis inizio fertilizzazione

In the final weeks of flowering, growers will cut down on nutrients to ease the transition to the pre-harvest process. At this time, a mild fertilizer with a nitrogen, phosphorus and potassium ratio of 4: 7: 10 is usually used.

How often to fertilize cannabis?

Usually, any fertilizer brand provides feeding tables to their customers. You will need to follow this type of chart to find out how often you need to fertilize cannabis properly. The nutrient table usually determines the growth cycle of 12-13 weeks. The week of the cycle is usually listed along the x-axis of the graph, which can also contain information about the weekly photoperiod (or more).

pH, EC and Water Temperature

Pianta di marijuana in fioritura pH, EC e temperatura dell'acqua

PH is a coefficient that indicates the acidity or alkalinity of the water. Later, as different types of cultivated soil require different pH adjustments, we will deepen the discussion. EC is the conductivity of our water, in other words, the amount of salt dissolved in the water. The more fertilizer our water contains, the higher the EC.

pH of the water

Even if all the necessary nutrients are present in the substrate, the plants will not be able to absorb them if the pH is wrong. The pH required for optimal nutrient uptake in soil differs from that of hydroponics. We show hydroponics and soil diagrams below.

PH is one of the most important parameters when preparing water for irrigation or fertilization of cannabis plants. It can be measured in several ways, but there is no doubt that if we want to be as accurate as possible, we must use digital meters and be well calibrated. The digital pH meter is a rather fragile laboratory instrument with a fragile probe. They must be handled with care and easy to maintain, but must be performed regularly.

The pH value is usually measured from 0 to 14. Considering that the pH 7 is a neutral value, our plants need to be fed with a weakly acidic pH. After adding fertilizers or stimulants to the irrigation water, the pH must always be measured, because these fertilizers or stimulants usually change the pH of the nutrient solution. The recommended pH of hemp crops in the soil is between 6 and 6.8.Generally, as flowering progresses, the growing cannabis plant needs a more acidic and more alkaline pH value, always staying within the range indicated above.

PH corretto dell'acqua fertilizzazione cannabis

EC of Water

This is the second parameter we need to know for proper irrigation and fertilization, we will need an accurate digital meter. Measuring the EC value of the water will help prepare water with good EC to add fertilizer and check the final EC of the nutrient solution after fertilizing.

To start fertilizing we must start with water with an EC close to 0.4, if we start with osmotic water (usually EC is between 0.0 and 0.2) and add calcium and magnesium, this is easy. If we don’t, nutritional deficiencies are likely to occur very soon.

There is no fixed table of ECs for all plants, different genetics also have different nutritional requirements (generally, rice-dominant plants will receive higher ECs than alfalfa-dominant plants), so our experience is very important. In addition to our knowledge of the plants we are growing, even in inert and hydroponic media, higher ECs are usually used.

Water temperature

The optimal temperature for irrigation water is between about 20 and 23 ยฐ C. Outside of these parameters, water of different temperatures will harm your crop.

Recognize nutrient problems

Too much or too little of the nutrients could cause stress and damage to the cannabis plant. For the following power issues, be sure to keep your eyes peeled.

Nutritional deficiencies

Malnutrition or nutrient blockage can lead to malnutrition. Lack of nitrogen, phosphorus, potassium, or secondary nutrients can cause symptoms such as dry leaves, yellow leaves. Nutritional deficiencies need to be addressed by adding more nutrients or by correcting nutrient blockade first.

Carenze nutrizionali foglie di piante di cannabis

Over fertilization

Overfeeding chemical fertilizers and boosters can burn cannabis plants. Some obvious signs of overfeeding turn out to be dry, burnt leaves that are yellow or brown discoloration, burnt edges, and upward curved tips. Over fertilization must be addressed quickly through root washing and a new nutrition program.

Cima resinosa, senza problemi di pH

Problems with pH

The pH problem can be caused by the imbalance of the culture medium, water and nutrients. Problems due to pH will seriously affect plant health and cause many other problems, such as nutrient lockout, insufficient nutrition, and so on. Problems due to pH will seriously hamper plant growth.

Organic vs Chemical Fertilizers, the differences

The organic nutrients, in addition to the seedlings, are also beneficial for the soil itself and support the development of a rich microbial ecosystem. Organic soil will also improve over time, making it ideal for outdoor growers. However, it must be said that chemical fertilizers also have their advantages. First, they are absorbed faster, which means they are better when efficiency is key.

๐ŸŒฟThe Grace Genetics  Team ๐ŸŒฟ

๐ŸŒฟThe Grace Genetics Team ๐ŸŒฟ

Cannabis in addition to being our job is also our passion, which is why we always strive to offer our readers quality articles that are always up to date on the latest news from the cannabis world.

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