Cannabis plants require balanced nutrition to grow healthily and produce high yields. Nutrient deficiencies are one of the most common problems for both novice and experienced growers. They can lead to yellow leaves, stunted growth, reduced flowering, and even plant death.
- Nitrogen deficiency (N)
Symptoms: Yellow leaves starting at the bottom leaves and spreading upward; slow growth.
Causes: Insufficient nitrogen in the diet, poor absorption due to incorrect pH.
Solution: Add a nitrogen-rich fertilizer during the vegetative stage; monitor the pH for optimal absorption.
- Phosphorus deficiency (P)
Symptoms: Dark green leaves with purple or red veins; delayed root and flowering development.
Causes: Nutrient deficiency, root environment too cold or poor pH.
Solution: Add phosphorus-rich nutrients, check medium temperature, correct pH.
- Potassium (K) deficiency
Symptoms: Yellow or brown edges on leaves, discoloration of leaves, weaker buds.
Causes: Insufficient potassium in the substrate or nutrient solution.
Solution: Add potassium-rich nutrients; check the water's EC if necessary.
- Magnesium deficiency (Mg)
Symptoms: Yellow spots between the leaf veins, curling leaves.
Causes: Poor magnesium absorption due to incorrect pH or deficiency in food.
Solution: Add magnesium through Epsom salt (MgSO₄) or special fertilizers.
- Iron deficiency (Fe)
Symptoms: Young leaves turn yellow while the veins remain green.
Causes: Too high pH or lack of iron in food.
Solution: Use iron-rich fertilizer and correct pH to optimal values.
- Other micronutrient deficiencies
Zinc (Zn): discolored and deformed leaves.
Manganese (Mn): brown spots between leaf veins, chlorosis.
Borer (B): deformed new shoots and flower tips.
Micronutrients are needed in small amounts but essential for healthy growth.
- Common causes of deficiencies
Incorrect pH: The most common cause of blocked nutrient absorption.
Overwatering or underwatering: affects root health and uptake capacity.
Inadequate or poor quality nutrition: Food should contain all macro- and micronutrients.
Temperature and stress factors: Extreme heat or cold reduces absorption efficiency.
- Prevention and correction
Measure pH and EC regularly: soil 6.0–6.8, coco/hydro 5.5–6.2.
Providing balanced nutrition: adjustments per growth phase (vegetative vs flowering).
Monitor root health: no root rot or overwatering.
Supplement micronutrients: if necessary, via foliar feeding or nutrient application.