# Brown, burnt leaf tips: likely causes and fixes

> Brown, burnt leaf tips on cannabis is most often Nutrient burn (feed too strong), Salt build-up in the root zone or Sodium build-up (softened water, coco, recirculation). How to tell them apart, the fix for each and what recovery looks like.

Also called: nute burn, burnt tips, crispy tips, tip burn, brown tips on leaves, nutrient burn.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=burnt-tips

## Likely causes, most likely first

### Nutrient burn (feed too strong) (Likely)

- Kind: Too much of something; urgency: Low urgency
- 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.
- Confirm: 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.
- Confirm: 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.
- Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)

### Salt build-up in the root zone (Less likely)

- Kind: Root zone; urgency: Deal with it this week
- Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth.
- Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning.
- Confirm: 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.
- Confirm: 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.
- Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like.
- Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)

### Sodium build-up (softened water, coco, recirculation) (Less likely)

- Kind: Too much of something; urgency: Deal with it this week
- 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.
- Confirm: 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.
- Confirm: 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.
- Confirm: 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.
- Article: [Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add](https://genetixbay.com/knowledge/nutrients/sodium.md)

### Air too dry / VPD too high (Less likely)

- Kind: Environment; urgency: Deal with it this week
- Fix: Raise RH or lower temperature to bring leaf VPD to 0.4-0.8 kPa (clones, seedlings), 0.8-1.2 (veg), 1.0-1.5 (flower). Humidifier, less exhaust when cool, fewer dry hot air inputs. Dry air also speeds spider mites.
- Recovery: Leaves flatten within a day.
- Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.
- Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH.
- Article: [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md)

### Spray or foliar burn (pesticide, oil, soap, foliar feed) (Less likely)

- Kind: Physical damage; urgency: Low urgency
- Fix: Stop spraying; rinse residue off with plain water at lights-off if damage is fresh. In future spray only at lights-off or with lights raised, test one leaf 24-48 h first, never mix sulfur with oils, and never spray buds.
- Recovery: No new damage on leaves that grow after the spray.
- Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth.
- Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers.
- Article: [What can I safely spray on plants in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md)

### Too much nitrogen (Less likely)

- Kind: Too much of something; urgency: Low urgency
- Fix: Cut feed N by 20-30% (or the whole feed EC by ~0.3-0.5 mS/cm); for a heavy overdose in containers, run a root-zone flush with pH-adjusted, quarter-strength feed to 20-30% runoff. In flower, taper N while keeping P, K, Ca, Mg, S and micros fed.
- Recovery: New leaves come in lighter green and flat within 5-7 days; clawed leaves relax partly.
- Confirm: 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.
- Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst.
- Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md)

### Wind burn from a fan blowing directly on leaves (Less likely)

- Kind: Environment; urgency: Low urgency
- Fix: Aim fans across and under the canopy, not straight at leaves: leaves should rustle, not thrash (roughly 0.3-1.0 m/s at leaf level). Damaged leaves stay damaged. Cannabis-specific evidence is grower observation.
- Recovery: No new damage on the fan side within a week.
- Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed.
- Article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md)

### Excess potassium crowding out magnesium and calcium (Less likely)

- Kind: Too much of something; urgency: Low urgency
- Fix: Stop K boosters and keep K near 175-250 mg/L; cation antagonism (K vs Mg and Ca) is the interaction that reliably matters in practice.
- Recovery: Interveinal yellowing stops climbing in 7 days.
- Confirm: 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.
- Confirm: 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.
- Article: [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md)

## Note

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.