Cannabis Plant Troubleshooting

Yellowing leaves are the single most common symptom new growers see — and the cause depends almost entirely on where on the plant the yellowing is and what stage you're in.

Brown spots on cannabis leaves can mean a nutrient deficiency, a fungal infection, or damage from water droplets and light. The pattern and location of the spots tells you which.

Leaf curling is the plant telling you it's stressed — the question is which direction, because up-curl (taco) and down-curl (clawing) have different causes.

Yellow or brown-tipped cannabis leaves are almost always nutrient burn. The fix is to feed less.

When cannabis leaves curl tip-down into a claw shape, you're usually overfeeding nitrogen. Sometimes it's overwatering.

White on cannabis leaves can mean powdery mildew (bad), trichomes (good), mite damage (bad), or calcium spots (bad). The pattern tells you which.

Brown, crispy edges on cannabis leaves usually mean potassium deficiency or nutrient burn — the pattern tells you which.

Root rot is a fast-moving, plant-killing disease caused by Pythium or similar oomycetes. Caught early, it's recoverable. Caught late, the plant dies within days.

Spider mites are the #1 pest for indoor cannabis. They're tiny (barely visible), breed fast, and can destroy a grow in under 2 weeks if left untreated.

Fungus gnats are tiny flying insects whose larvae eat cannabis roots. Adults are annoying but harmless — the larvae in the soil do the real damage.

Aphids are small pear-shaped insects (usually green, sometimes black/pink) that cluster on stems and new growth, sucking sap and weakening the plant.

Cannabis caterpillars — usually corn earworms or tobacco budworms — bore INTO buds and eat them from inside. By the time you see damage, they're already eating your harvest.

Purple stems can be normal genetics, an early sign of phosphorus deficiency, or cold stress. Location and age of the plant tell you which.

Overwatering is the single most common beginner mistake. The plant can't get oxygen to its roots, so it drowns — even though it looks like it needs water.

Underwatering causes limp, thin plants with crispy leaves. Unlike overwatering (heavy leaves), underwatered plants look dried out and papery.

Cannabis stops growing efficiently above 82°F. Prolonged heat causes stretchy, lanky plants, tacoed leaves, and foxtailing in flower.

Cannabis stops growing efficiently below 65°F. Prolonged cold causes purple stems, slow growth, and weak plants — and frost kills outright.

Light burn happens when your grow light is too intense or too close. It bleaches top leaves white-yellow and can ruin cola tips.

Stretchy seedlings are thin, tall, and fall over — a sure sign the light is too far away or too weak. Caught early, easy to fix.

Drooping leaves mean a watering problem — but whether it's too much or too little depends on HOW they droop.

If your plant looks healthy but just isn't growing, the issue is usually environmental — not nutrient-based. Go through the checklist.

Foxtailing is when a cannabis cola grows new bud tips out the top mid-flower, creating a fox-tail shape. Usually it's stress, occasionally genetics.

Stunted growth is when your plant stops progressing — not just slow, but nearly frozen. Almost always root-related or a major stress.

Nutrient burn is when you give more nutrients than the plant can use. The tips go yellow, then brown, then crispy. Very common when growers follow bottle doses (usually 2-3x too strong).

Nitrogen is the most-used nutrient during vegetative growth. A deficiency shows up fast: pale green, then yellow, working up from the bottom leaves.

Calcium deficiency is extremely common in coco coir grows and when using RO or filtered water. It shows up as small rust-colored spots and distorted new growth.

Magnesium is mobile in the plant, so deficiency shows up on lower leaves first — the plant pulls Mg from old leaves to feed new growth.

When your water or soil pH is outside the plant's absorption range, roots can't take up nutrients — even if there's plenty available. This looks like multiple deficiencies at once.

Too much nitrogen — easy to do during veg — causes dark green clawing leaves, burn, and delayed flowering.

Powdery mildew (PM) is a fungal disease that coats leaves in white powder. It spreads fast, weakens the plant, and makes buds unsellable.

Bud rot (Botrytis cinerea) is the worst disease in cannabis flowering. It rots buds from the inside out, turning flowers into gray mush.