Potassium deficiency (K)
Color change & Spots / Dots

Potassium deficiency (K)

📍
Old / Lower Leaves, Leaf Margins, Leaf Tips
📈
Very slow growth, Gradually worsened, Normal growth
Yellow leaf margins Brown leaf margins Brown leaf tips Necrosis / dead tissue Dry / papery spots
⚠️ Verwechslungsgefahr

Kaliummangel zeigt sich typischerweise zuerst an älteren Blättern und beginnt häufig an Blatträndern und Spitzen. Charakteristisch sind aufhellende bis gelbliche Randbereiche, die später trocken, braun und nekrotisch werden. Im Unterschied zu vielen frischen Spurenelementmängeln sitzt das Problem nicht zuerst im Neuwuchs, sondern eher im älteren Laub. Gerade wenn Blattränder regelrecht ausbrennen, sollte nicht vorschnell nur an zu wenig Kalium gedacht werden, sondern auch an gestörte Verfügbarkeit, Wurzelstress oder ein insgesamt instabiles Milieu im Substrat.

Go to solution

Ursachenforschung: Was ist passiert?

Excessive amounts of calcium or magnesium can block potassium uptake (antagonism). The deficiency often occurs during peak bloom, when the plant requires massive amounts of potassium for cell turgor and sugar transport into the flowers.

Systemische Einordnung

What is often really behind it

A deficiency is often a problem of availability. A visible deficiency does not automatically mean that this nutrient is absent in the substrate. Often, absorption in the root zone is disrupted by pH fluctuations, excessive moisture, cold, or an unstable soil environment. Especially in the living soil approach, it is therefore not about hastily addressing symptoms with more fertilizer, but about carefully assessing the availability and balance in the soil.

Common associated problems

pH problem / nutrient lockout
Discoloration · Spots / Dots · Abnormal Growth · Deformation / Deformed Growth

pH problem / nutrient lockout

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Over-fertilization
Color change · Deformation / Deformed Growth · Abnormal Growth

Over-fertilization

Check problem →
Overwatering / Waterlogging
Drooping / wilting plant parts · Conspicuous growth

Overwatering / Waterlogging

Check problem →
✓ Grow Lab expert solution

The right treatment

Potassium is responsible for your cannabis plants' immune system and strength. In case of a deficiency, you should first gently flush the substrate with pH-regulated water (pH 6.3) to resolve any salt blockages caused by too much calcium. Afterward, apply a full dose of a potassium-rich bloom fertilizer.

Potassium is a highly mobile nutrient, so the spread of brown edges should stop within a few days after application. Ensure that the humidity is not too low, as potassium regulates the plant's water balance; in extreme dryness, the deficiency will worsen.

An organic immediate remedy is kelp extract or wood ash tea (dose carefully due to high pH). Stable stems and plump calyxes are the goal of a successful potassium correction.

Remember: potassium deficiency makes your plants extremely susceptible to heat stress and mold (mildew).

Expert tools for the next step

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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