Yellow leaves are one of the most common signs that something is wrong with cannabis plants. While it's sometimes a natural process during flowering, premature or extensive yellowing often indicates nutrient problems, stress, or disease.
- Natural yellowing
Sometimes turning yellow is normal:
Older leaves: Leaves at the bottom of the plant may turn yellow and fall off during late flowering.
Aging: The plant concentrates its energy on new buds, older leaves die off.
Please note: This is normal when only a few lower leaves turn yellow.
- Feeding problems
a. Nitrogen deficiency (N)
Symptoms: Yellow leaves start at the bottom leaves and spread upwards.
Solution: Feed with a nitrogen-rich fertilizer during the vegetative phase.
b. Magnesium deficiency (Mg)
Symptoms: Yellow spots between the leaf veins, leaves sometimes curl.
Solution: Use magnesium-containing fertilizers or Epsom salts.
c. Other shortages
Iron (Fe): young leaves yellow, veins remain green.
Potassium (K): Leaves turn yellow and burn at the edges.
- Overwatering or root problems
Too much water can lead to oxygen deficiency in the roots.
Roots rot and cannot absorb nutrients.
Symptoms: Leaves turn yellow, limp and often fall off.
Solution:
Allow the top 2–3 cm of soil to dry out before watering again.
Provide good drainage and ventilation in the pot.
- pH problems
Too high or too low pH disrupts nutrient absorption.
Symptoms: yellowing, brown edges or spots, sometimes entire plant.
Solution:
In soil: pH 6.0–6.8
In coco or hydro: pH 5.5–6.2
Check regularly and adjust if necessary.
- Pests and diseases
Root rot (Pythium): causes yellowing and drooping of leaves.
Fungi: Some fungi cause mottled or yellowing leaves.
Insects: Aphids and spider mites can turn the leaves yellow.
Solution:
Inspect the plant regularly.
Use biological or chemical control where necessary.
Remove severely affected leaves.
- Stress factors
Too much light or heat can burn leaves and cause them to turn yellow.
Cold or temperature changes cause stress.
Rapid changes in nutrition or watering can accelerate yellowing.
- Prevention and care
Keep the diet balanced and adjust to the growth phase.
Measure the pH and EC of water and nutrient solutions regularly.
Ensure adequate ventilation and correct temperature.
Inspect plants regularly for pests and diseases.
Only remove naturally yellowing leaves if they are hindering the plant.