Color Change & Spots / Dots & Noticeable Growth

CalMag Imbalance

📍

Affected area Whole plant, Old / lower leaves, New leaves / shoot tips

📈

Wachstums-Check Very slow growth, Gradual worsening, Growth arrest / Stagnation

Erkennungsmerkmale

⚠️ Verwechslungsgefahr

Ein CalMag-Ungleichgewicht zeigt sich selten als sauberer Einzelmangel. Typisch ist ein gemischtes Schadbild aus interveinalen Aufhellungen, rostigen Flecken, trockenem Gewebe, gestörtem Neuwuchs und insgesamt instabiler Entwicklung. Die Pflanze wirkt nicht einfach nur „zu hell“ oder „zu dunkel“, sondern zeigt mehrere Spannungszeichen gleichzeitig. Genau dieses Mischbild ist der wichtigste Hinweis: Es geht hier meist nicht um einen isolierten Calcium- oder Magnesium-Mangel, sondern um ein Verhältnisproblem in Aufnahme, Verfügbarkeit und Wurzelmilieu. Fachlich passt das gut dazu, dass Calcium und Magnesium im Substrat- und Wasserhaushalt eng zusammenhängen und dass hoher pH sowie hohe Alkalinität die Verfügbarkeit zusätzlich verschieben können.

Go to solution

Ursachenforschung: Was ist passiert?

Cannabis has an extremely high magnesium requirement for photosynthesis under full-spectrum LED light. Soft water or a pH value below 6.0 often result in the plant being unable to absorb enough magnesium, even if it is present in the fertilizer.

Systemische Einordnung

What is often really behind it

A deficiency is often a problem of availability. Not every visible deficit is a true deficiency. In many cases, nutrients are present in the soil but are no longer readily available to the plant due to pH shifts, salt stress, overly wet conditions, or a disturbed root zone. Especially in the living soil approach, soil life plays a central role: only an active, stable microbiome can reliably buffer, transform, and keep nutrients plant-available. Lockout is therefore usually not a simple fertilization problem, but a sign that the system in the root zone has become unbalanced.

You should check these causes first

✓ Grow Lab expert solution

The right treatment

To solve this common cannabis problem, you need to adjust the calcium to magnesium ratio in your irrigation water to approximately 3:1. First, check the pH value; for soil, a range of 6.2 to 6.7 is ideal for magnesium absorption.

For acute symptoms, foliar feeding with Epsom salts (magnesium sulfate) helps extremely quickly: dissolve 0.5 g in 1 liter of water and spray the leaves shortly before the dark period.

For a continuous supply, you should use a CalMag additive, especially if you are growing with osmosis water or very soft tap water. A stable CalMag ratio not only ensures green leaves but is also the basic prerequisite for the plant to be able to form heavy, dense buds during flowering without premature nutrient depletion.

Passende Ratgeber aus dem Magazin

Experten-Wissen

The problem isn't your fertilizer – your tap water is sabotaging your grow.

Experten-Wissen

CalMag 2:1, 3:1 or 4:1 - Which Ratio is Right?

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After diagnosis, the right decision counts

Not every symptom requires the same next step. If you're specifically looking for the right Living Soil input, our Nährstoff-Finder can help. If you want to strategically align your setup to pot size, experience, goal and nutrients, our Living Soil Navigator will guide you further.

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