Tan, crispy scorched edges on older leaves

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.

1. PossiblePotassium deficiency

   NutrientDeal with it this weekRead: Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance

   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.

2. PossibleNutrient burn (feed too strong)

   Too much of somethingLow urgencyRead: Brown or burnt leaf tips on cannabis: a differential

   Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up).

   Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay.

   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.
   • Pour-through extraction for container pH and EC. Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable.

3. Less likelyAmmonium toxicity (too much NH4 in the feed)

   Too much of somethingDeal with it this weekRead: Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets

   Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH.

   Recovery: pH stops falling and new leaves lose the dark claw within a week.

   How to confirm it

   • Measure input pH and root-zone (runoff or reservoir) pH. Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.
   • Look at the roots. Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.

4. Less likelyManganese toxicity (usually low pH)

   Too much of somethingLow urgencyRead: Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance

   Fix: Raise root-zone pH into range (soilless 5.8-6.2, soil 6.2-6.8); check that the micro mix is not over-dosed. Tissue tests may not flag it: in one trial, symptomatic plants had normal leaf Mn.

   Recovery: Margin yellowing stops climbing within 7 days.

   How to confirm it

   • Measure input pH and root-zone (runoff or reservoir) pH. Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.
   • 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.

5. Less likelySodium build-up (softened water, coco, recirculation)

   Too much of somethingDeal with it this weekRead: Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add

   Fix: Never use ion-exchange softened water. Keep feed sodium below about 50 mg/L (more than ~5 mM NaCl, 115 mg/L Na, may cut hydro yield and cannabinoids fall as NaCl rises). Dump and refill recirculating reservoirs more often; rinse coco before planting.

   Recovery: Tip burn stops advancing on new leaves within a week.

   How to confirm it

   • 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.
   • 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.
   • 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.

6. Less likelyBoron toxicity

   Too much of somethingLow urgencyRead: Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window

   Fix: Test the water (some wells carry B) and stop extra boron products; supply only 0.2-0.5 mg/L B in total. Cannabis tolerated about 10x for weeks, but symptoms appeared after 7 weeks at ~4.9 mg/L.

   Recovery: No new margin scorch on leaves that mature after the change.

   How to confirm it

   • 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.

7. Less likelyChloride excess (salinity)

   Too much of somethingLow urgencyRead: Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add

   Fix: Keep chloride below about 50-70 mg/L in the feed; switch potassium chloride for potassium sulfate; blend high-chloride water with RO.

   Recovery: No new tip burn after the change.

   How to confirm it

   • 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.
   • 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.

8. Less likelyMolybdenum deficiency

   NutrientLow urgencyRead: Molybdenum (Mo) in cannabis: the trace element nitrate depends on

   Fix: Almost never the answer: cannabis grown 9 weeks without Mo showed no visible symptoms. Correct low pH (Mo availability falls as pH drops); supply about 0.01-0.05 mg/L Mo via a complete micro mix.

   Recovery: Pale middle leaves stop spreading after pH correction.

   How to confirm it

   • 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.
   • Measure input pH and root-zone (runoff or reservoir) pH. Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.

Look for

Tan-brown dry band along the margins of lower fan leaflets with a yellow transition zone..