Cannabis Troubleshooting Flowchart: Diagnose Any Problem in 5 Steps

When something goes wrong with your plant, the worst thing you can do is guess and throw solutions at it. Most cannabis problems have a specific cause, and misdiagnosing leads to making the problem worse. This guide is a systematic flowchart: start with what you see, follow the decision tree, arrive at the most likely cause, and get the specific fix.

Before you start: check these three things first. They cause the majority of cannabis problems and should be verified before investigating anything else:

1. pH: is your input water between 6.0–6.8 (soil) or 5.5–6.5 (coco/hydro)? If not, fix this first — most nutrient problems are actually pH problems. See our pH guide
2. Watering: is the medium wet or dry? Does the pot feel heavy (overwatered) or light (underwatered)?
3. Light distance: has anything changed with your light height or intensity recently?

If all three check out, proceed to the symptom below.

Symptom 1: Yellow leaves

Where are the yellow leaves?

Bottom leaves only → Nitrogen deficiency (most likely)

• Nitrogen is mobile — the plant pulls it from old leaves to feed new growth
• Older fan leaves turn uniformly pale green, then yellow, then drop
• New growth stays green
• In late flower: this is normal. The plant naturally cannibalizes lower leaves during senescence. No action needed unless it's aggressive
• In veg or early flower: increase nitrogen in your feed. Check pH first — nitrogen lockout occurs below pH 5.5 and above pH 7.5
• See our deficiency chart

Top/new growth → Iron deficiency or light burn

• If the yellowing is between veins (interveinal chlorosis) on new leaves: iron deficiency. Common at high pH (above 6.8 in soil). Fix pH, add chelated iron
• If the yellowing is bleaching/whitening of leaves closest to the light: light burn. Raise the light 6–12 inches or reduce intensity. See our light burn guide

All leaves, uniformly → pH lockout

• When pH is outside the acceptable range, multiple nutrients become unavailable simultaneously
• The plant yellows everywhere, doesn't respond to additional nutrients
• Flush the medium with correctly pH'd water, then resume feeding at correct pH
• See our pH lockout guide

Yellowing between veins (lower leaves) → Magnesium deficiency

• Interveinal chlorosis on lower/middle leaves — the tissue between veins turns yellow while veins stay green
• Common in coco grows (coco binds magnesium) and with RO water (no mineral content)
• Fix: cal-mag supplement. See our cal-mag guide

Yellowing between veins (upper leaves) → Iron deficiency

• Same interveinal pattern but on NEW growth (iron is immobile)
• Almost always a pH issue — iron locks out above pH 6.8 in soil
• Fix: lower pH. Chelated iron as a temporary supplement

Symptom 2: Brown or burnt leaf tips

How much of the tip is burnt?

Just the very tips (1–3mm) → Mild nutrient burn

• The plant is getting slightly more nutrients than it can use
• Reduce feed strength by 10–20%
• Monitor: if it doesn't progress, you're close to the plant's tolerance. Some tip burn is normal in aggressive feeding regimens

Tips + edges browning progressively → Moderate nutrient burn

• Reduce feed strength by 30–40%
• Check EC/PPM of your feed AND runoff. If runoff EC is significantly higher than input, salts have accumulated — flush with plain pH'd water, then resume at lower concentration
• See our EC guide

Brown crispy edges (not tips) → Potassium deficiency or heat stress

• If edges brown and curl upward: heat stress. Check temperature at canopy level — should be 72–82°F. Raise the light, improve airflow, or reduce ambient temperature
• If edges brown from the outside in, lower leaves first: potassium deficiency. Check pH (K locks out below 5.5), increase K in feed

Symptom 3: Spots on leaves

What do the spots look like?

Small brown spots (rust-colored) → Calcium deficiency

• Small, irregularly shaped brown spots scattered across leaves
• Often accompanied by curling leaf edges
• Common in coco (coco binds calcium) and with RO or soft water
• Fix: cal-mag supplement, check pH (Ca locks out below 6.2 in soil)
• See our cal-mag guide

Small yellow spots (speckles) → Spider mites

• Tiny yellow dots (stippling) on the top of leaves
• Check the underside of leaves with a loupe — mites are tiny (0.5mm), round, and may have webbing
• See our pest guide

White powdery spots → Powdery mildew

• White, powdery coating on leaf surfaces
• Starts as small circular patches, spreads rapidly
• Caused by poor airflow + high humidity
• See our powdery mildew guide

Large irregular brown patches → Leaf septoria or nutrient splash

• If patches have a yellow halo: leaf septoria (fungal). Remove affected leaves, improve airflow, apply neem or copper fungicide
• If patches are random and don't spread: nutrient solution splashed on the leaf and burned it under light. Not a disease — avoid getting nutrient water on leaves

Symptom 4: Wilting / drooping

Is the medium wet or dry?

Medium is wet (heavy pot) → Overwatering

• Leaves droop uniformly, including the petioles (stems)
• The entire plant looks limp and heavy
• Let the medium dry out completely before watering again
• Check drainage — ensure the pot has holes and water isn't pooling
• See our overwatering guide

Medium is dry (light pot) → Underwatering

• Leaves droop but look thin and papery (not plump)
• Petioles may point downward while leaf blades curl slightly upward
• Water thoroughly until 10–20% runoff
• If severely wilted, water in stages — a small amount, wait 15 minutes, then water fully

Medium is wet AND leaves are wilting after days → Root rot

• The plant wilts despite wet medium because damaged roots can't absorb water
• Check roots: they should be white and firm. Brown, slimy, foul-smelling roots = root rot
• See our root rot guide

Wilting only during lights on, recovers during lights off → Heat or light stress

• The plant can't transpire fast enough under intense light/heat
• Check canopy temperature — hold your hand at canopy height for 30 seconds. If it's uncomfortably warm, it's too hot for the plant
• Raise the light, improve ventilation, or add an oscillating fan

Symptom 5: Curling leaves

Which direction?

Curling upward (taco-ing) → Heat stress or light stress

• Leaves fold upward along the midrib, like a taco
• The plant is trying to reduce light-exposed surface area
• Fix: raise light, lower temperature, improve airflow
• See our light burn guide

Curling downward (clawing) → Nitrogen toxicity or overwatering

• If leaves are dark green AND clawing: nitrogen toxicity. The plant has excess nitrogen — leaves turn very dark green and curl downward. Reduce nitrogen in feed. See our nitrogen toxicity guide
• If leaves are normal green AND drooping/clawing: overwatering. Let the medium dry out

Edges curling upward (canoeing) → Heat or low humidity

• Leaf edges curl up while the center stays flat
• Usually a VPD problem — temperature too high relative to humidity
• See our VPD guide

Twisting or irregular curling → pH swings or root problems

• Leaves that twist or curl asymmetrically usually indicate root zone issues
• Check pH of input AND runoff
• Inspect roots if possible

Symptom 6: Slow or stunted growth

When did growth slow?

Sudden stop after a change → Stress response

• After transplanting: transplant shock. Normal — wait 3–7 days for recovery. See our transplant guide
• After topping or heavy training: recovery period. Normal — wait 3–5 days
• After changing nutrients or pH: check input pH and EC. Sudden changes stress roots

Gradual slowdown → Root-bound, pH creep, or environmental issue

• Root-bound: roots circling the bottom of the pot, visible through drainage holes. Transplant to a larger container
• pH creep: pH of the medium has drifted over time. Check runoff pH — if it's significantly different from input pH, flush and recalibrate
• Low light: during winter or with aging LEDs, light output decreases. Check PPFD at canopy level
• Temperature: growth slows below 65°F and above 85°F

Growth slow from the start → Bad genetics, poor seedling conditions, or contaminated medium

• Some seeds produce weak plants. If all other conditions are correct, it may be genetics
• Check for fungus gnats in the medium — larvae feed on root hairs and slow growth in seedlings. See our pest guide

Symptom 7: Discoloration other than yellow

What color?

Dark green (almost black) → Nitrogen toxicity

• Leaves are unnaturally dark green, often with a waxy sheen
• Usually accompanied by downward clawing
• Reduce nitrogen immediately
• See our nitrogen toxicity guide

Purple stems or petioles → Genetic or phosphorus deficiency

• If the plant is otherwise healthy and growing well: genetic. Many strains have naturally purple stems
• If accompanied by slow growth, dark leaves, or poor flower development: phosphorus deficiency. Check pH (P locks out below 5.5 and above 7.0)
• See our color expression guide

Red or pink stems/leaves → Phosphorus deficiency or cold stress

• Check root zone temperature — below 60°F impairs phosphorus uptake
• Check pH — phosphorus availability drops sharply below 6.0 in soil

Brown patches on buds → Bud rot (Botrytis)

• Gray-brown spots on buds, often starting inside dense colas
• Mushy texture, gray fuzz visible under magnification
• Remove affected buds immediately — cut 1 inch below the infected area
• See our bud rot guide

The 5-step diagnostic process

When you encounter a problem:

1. Check pH — test input water pH, test runoff pH. If either is out of range, fix it and wait 48 hours before doing anything else
2. Check watering — lift the pot. Is it too heavy (wet) or too light (dry)? Adjust watering before adding nutrients
3. Check environment — temperature, humidity, light distance. Use a thermometer at canopy level, not room level
4. Identify the symptom pattern — WHERE on the plant (top, bottom, everywhere), WHAT it looks like (yellowing, spots, curling, wilting), and HOW FAST it's progressing
5. Make ONE change — fix the most likely cause and wait 48–72 hours. Multiple simultaneous changes make diagnosis impossible if the problem persists

For the AI-powered diagnostic tool, visit Plant Doctor. For a visual nutrient deficiency reference, see our deficiency chart.