Why are macronutrients so important for cannabis?
Cannabis plants require a balanced supply of nutrients to grow healthily and develop high-quality flowers. The three primary nutrients (macronutrients) – nitrogen (N), phosphorus (P), and potassium (K) – are crucial for every growth phase. A deficiency or excess can lead to stunted growth, reduced yields, or even plant death.
In this guide, we explain:
✔ The functions of N, P & K in each phase
✔ Identifying deficiencies and excesses
✔ Optimal NPK ratios for growth and flowering
✔ Tips for correcting nutrient problems
Nitrogen (N) – The growth boost
Role of Nitrogen in Cannabis Cultivation
Nitrogen is the most important nutrient during the vegetative phase, as it is responsible for the formation of chlorophyll, proteins, and amino acids. A good nitrogen supply ensures strong, dark green leaves and rapid growth.
Detect and correct nitrogen deficiency
- Symptoms: Yellow leaves (starting at the bottom), slow growth, weak stems
- Causes: Too little fertilizer, incorrect pH value (optimal: 6.0–7.0 in soil, 5.5–6.5 in hydroponics)
- Solution: Use nitrogen-rich fertilizer (e.g. blood meal) or correct pH value
Avoid excess nitrogen
- Symptoms: Dark green, “burned” leaves, inhibited flowering
- Solution: Reduce fertilization, flush with clean water
Phosphorus (P) – The flower booster
Why Phosphorus Is Crucial During the Flowering Phase
Phosphorus supports root formation, energy transfer, and flower development. Especially during the flowering phase, it promotes dense, resinous buds and strengthens the plant against stress.
Phosphorus deficiency – these are the signs
- Symptoms: Dark green or purple discoloration on leaf edges, stunted growth
- Solution: Apply phosphorus-containing fertilizer (e.g. Bat Guano), aerate the root area
Beware of excess phosphorus!
- Consequences: Blocks the absorption of zinc, iron and calcium
- Countermeasure: Choose fertilizer with a balanced NPK ratio
Potassium (K) – The immune system booster
Functions of Potassium
Potassium regulates water balance, activates enzymes, and strengthens defenses against fungi and pests. It is essential during both the growth and flowering phases.
Potassium deficiency: How to react correctly
- Symptoms: Yellow leaf tips with brown spots, limp leaves
- Treatment: Use potassium-rich fertilizer (e.g. wood ash)
Too much potassium? Here’s what you can do
- Problem: Leads to magnesium and calcium deficiency
- Solution: Adjust fertilization, add calcium-magnesium (CalMag) if necessary
NPK ratio – Finding the perfect balance
- Vegetative phase: Higher nitrogen content (e.g. 3-1-2)
- Flowering phase: More phosphorus and potassium (e.g. 1-3-2)
- Special tip: Organic fertilizers (e.g. compost tea) naturally promote nutrient absorption
Conclusion – Healthy plants through optimal nutrient supply
The correct dosage of nitrogen, phosphorus, and potassium is key to strong cannabis plants and abundant yields. Regularly check leaf color and growth to detect deficiencies early.
For more in-depth tips, we recommend the “Trinity of Modern Cultivation” manual from Treez Tools – a must-have for every grower!