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How do I know the nutritional needs of my cannabis plant?

22.March 2021 | Manuela

Person with blue gloves and a magnifying glass in one hand examines a cannabis plant

Plants are a miracle of nature. They provide us with many things and in turn can communicate exactly what they need. The cannabis plant also lets us know exactly what it wants to order from the "cannabis menu". How to interpret the plant's signs, and in which environment it prefers to dine, we explain in the following blog.

First things first: the right environment for the cannabis plant

A dignified meal belongs in an appropriate environment. What is true for humans is no different for the cannabis plant. You can look at leaf edges and discoloration for as long as you want, but if the environment is not right, even the best fertilizer is no solution. So the very first thing to look at is basic environmental factors such as temperature, ventilation and watering.

Temperature

In the first phase of life between 20 and 24 °C, in the second half of life between 20 and 27 °C, these are the generally accepted guidelines for temperature.

Ventilation

When it comes to ventilation, the rule is: as natural and clean as possible. If you would like to know in more detail which values Grünkraft adheres to and how Alpine air can be made even cleaner, you are welcome to take a detour at this point in the direction of "CBD indoor plant - feel-good zone in cold days".

Irrigation

When it comes to irrigation, the basic rule is that plants do not like wet soil. There are systems to water the plants automatically, these can be adapted to plant stage, genetics and temperature. An experienced grower knows, however, that each plant has individual needs and a trained eye cannot be replaced by automatisms. Once finger in the soil and test is still the safest method.

From this you can see if the cannabis plant can absorb nutrients

So far so good. The temperature is comfortable and the drinks are taken care of, it can be served. From here on, two values should be checked regularly, because they tell us whether the cannabis plant can absorb the nutrients and whether it is getting too much or too little of the individual components. From now on, the four letters of confidence are: pH and EC.

pH value

The pH establishes how acidic or basic an aqueous solution is. In our case, the drainage water gives us information about the pH of our soil. This value should be monitored regularly. If plant soils are too acidic or alkaline, cannabis plants will not be able to root through the soil and chemical processes to process nutrients will be disrupted. The ideal pH for cannabis is between 6.0 and 7.0, with the composition of the soil determining the fine-tuning.

EC value

The "EC" in "EC value" stands for "electircal conductivity" and indicates how strong the ability of a substance is to conduct electric current. In cannabis cultivation, the conductivity of fertilizer or drainage water is measured. Plant nutrients are all minerals and as such affect the conductivity of water. An EC meter should be used regularly to check whether the soil of the plants is optimally loaded with nutrients. For young plants, the ideal value is between 1.2 - 1.4 mS/cm. For older plants, it should be a maximum of 2.4 mS/cm. If the EC value is too low, the plant will start to show deficiencies and suffer from malnutrition. If the level is too high, the plant becomes overfed and its leaves become "strained", develop brown spots and begin to curl up. The chances of survival are low and any crop yields will be smaller.

How to recognize deficiency or overfertilization symptoms in a cannabis plant

If all the environmental factors are in balance and the flowers are still not thriving as they should, the problem is probably nutritional. We discussed what nutrients the cannabis plant needs and what needs are met with them in our last blog post on "The Cannabis Menu". Now it's a matter of knowing if the plant is getting exactly what it needs and how it is communicating any supply errors to us.

Fertilizing is a science in itself, and euphoric overfertilizing in particular is severely punished. The following table is intended to provide an overview of the most important nutrients and their trapdoors.

Nutrient
Deficiency symptom
Overfertilization phenomenon
Nitrogen (N)
Lightening of the leaf • Start with the oldest leaves
Very dark green leaves • Long and thin stems • Delayed maturation and reduced growth • Poor root system
Phosphorus (P)
Dark green, wizened leaves • Older leaves turn yellow • Brown-purple spots on the leaves • Purple discoloration on petioles and stems
Young leaves remain small and curled • Premature ripeness • Excess phosphorus prevents absorption of zinc, magnesium and copper
Potassium (K)
Oldest leaves get brown edges • Yellowing and death of the whole leaf • Thin stems • Small seeds
Leaf desiccation • Burn symptoms • Excess potassium prevents absorption of magnesium and calcium
Calcium (Ca)
Young leaves with yellow spots and brown edges • Delayed growth and reduced production
The plant becomes very dark • Can increase the pH value of the soil • Excess calcium prevents the absorption of magnesium, boron and copper
Magnesium (Mg)
Lightening of the older leaves • Yellow to rusty brown discolorations
Deep green color of the leaves • Delayed growth
Sulfur (S)
Purple coloration of the stems • Delayed growth and flowering
Deep green color of the leaves • Very slow development
Iron (Fe)
In young leaves, a strong yellowing between the leaf veins
Uptake of phosphates is disturbed

Fertilizing cannabis plants - easier said than done

The table gives you an idea: Fertilizing is easier said than done. Overfertilizing one substance, can inhibit the uptake of another. Individual deficiencies show the same symptoms with different nutrients. Combine this with the fact that plant needs are different at each stage of growth. Leaf coloration and growth are different for each genetic, and a purple may be a hoped-for tint in a harlequin, while it is a sign of disease in other varieties. Again, the old adage applies: there is no substitute for a grower's experience.

Now we know what belongs on a cannabis menu and can roughly estimate how the plant places its order. In the next part, we will devote ourselves to the Grünkraft Witch's Kitchen and reveal how our in-house fertilizer chef conjures up our plants' favorite menus.

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