Common Cannabis Growing Problems and How to Fix Them
Yellow leaves, slow growth, burnt tips — diagnose and fix the most common issues home growers face.
Yellowing leaves
Yellowing is one of the most common issues and has several causes. Nitrogen deficiency starts with lower leaves yellowing and progresses upward — increase nitrogen in your feed. Overwatering causes general yellowing with drooping leaves and soggy soil — let the medium dry out more between waterings. pH imbalance locks out nutrients even when they're present in the soil — check and correct your pH (6.0–7.0 for soil, 5.5–6.5 for hydro). Natural senescence (lower leaves yellowing late in flower) is normal and not a cause for concern.
Nutrient burn
Brown, crispy tips on leaves are the classic sign of nutrient burn — you're feeding too much. Flush the medium with plain pH-adjusted water and reduce your nutrient concentration by 25–50%. Nutrient burn is more common with synthetic nutrients than organic. Prevention is better than cure: always start at half the recommended dose and increase gradually based on how the plant responds.
Overwatering
Overwatering is the number one killer of cannabis plants, especially for beginners. Symptoms include drooping leaves that feel firm (not limp like underwatering), slow growth, and yellowing. The fix is simple: water less frequently. The correct watering frequency depends on pot size, plant size, and environment, but a reliable method is the 'lift test' — lift the pot when dry and when wet to learn the weight difference, then water only when it feels light. Always ensure your pots have drainage holes.
Pests: spider mites, fungus gnats, and aphids
Spider mites leave tiny white dots on leaves and fine webbing under them — treat with neem oil spray or predatory mites. Fungus gnats are small flies whose larvae damage roots — let the top inch of soil dry out completely between waterings and use yellow sticky traps. Aphids cluster on new growth and under leaves — neem oil, insecticidal soap, or ladybirds (outdoors) are effective. Prevention is key: keep your grow space clean, inspect new plants before introducing them, and maintain good airflow.
Powdery mildew
Powdery mildew appears as white, powdery spots on leaves and stems. It thrives in high humidity with poor airflow. Remove affected leaves immediately and treat with a diluted hydrogen peroxide spray (3% H2O2 diluted 1:10 with water) or a potassium bicarbonate solution. Improve airflow and reduce humidity below 50% in flower. Prevention: maintain good air circulation, avoid overcrowding plants, and keep humidity in check.
Slow or stunted growth
Slow growth can result from several factors: root-bound plants (transplant to a larger pot), cold temperatures (keep above 18°C), insufficient light (check your DLI — daily light integral), overwatering, or pH imbalance. Check each factor systematically rather than changing multiple things at once. The most common cause in small tents is insufficient light — a 200W LED in a 60x60cm tent is the minimum; 300W+ is better.