Dark brown lesions on sugar leaves in flower
Starts mid-flower on sugar leaves, followed by tip and margin browning on fan leaves..
- Also called
- sugar leaves turning brown
- brown spots on bud leaves
- dark sugar leaf tips
Likely causes, most likely first
Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.
PossiblePotassium deficiency
Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K.
Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins.
How to confirm it
- Measure runoff EC against input EC. Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed.
- Get a water report (or test your water). Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium.
- Leaf tissue analysis. Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency.
- Watch new growth for 5-10 days after one change. Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days.
Look for
Dark brown blotches on small leaves sticking out of buds; pull one to check the bud inside for rot..
The full guide: Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance
Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.
