# Yellow then tan edges on new leaves: likely causes and fixes

> Yellow then tan edges on new leaves on cannabis is most often High root-zone pH locking out iron, manganese, zinc, boron and copper, Calcium deficiency (often a delivery problem) or Zinc deficiency. How to tell them apart, the fix for each and what recovery looks like.

Also called: new leaves brown edges, yellow margins on top leaves, edges of new growth dying.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=yellow-new-margins

## Likely causes, most likely first

### High root-zone pH locking out iron, manganese, zinc, boron and copper (Possible)

- Kind: pH; urgency: Deal with it this week
- Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5).
- Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days.
- Confirm: 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.
- Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter.
- 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: 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: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)

### Calcium deficiency (often a delivery problem) (Less likely)

- Kind: Nutrient; urgency: Deal with it this week
- Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth.
- Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay.
- 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: 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.
- 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: 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: 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.
- Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md)

### Zinc deficiency (Less likely)

- Kind: Nutrient; urgency: Low urgency
- Fix: Lower high pH, stop excess phosphorus 'boosters' (high P ties up Zn), then supply about 0.1-0.5 mg/L Zn as zinc sulfate or chelate.
- Recovery: New leaves reach normal size with clean margins in 7-14 days.
- Confirm: 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.
- 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: 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: [Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link](https://genetixbay.com/knowledge/nutrients/zinc.md)

### Excess phosphorus (bloom boosters) inducing Zn, Fe and Ca shortages (Less likely)

- Kind: Too much of something; urgency: Low urgency
- Fix: Drop the booster. Keep P at about 30-60 mg/L; four controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, and excess P just leaves in the runoff.
- Recovery: New growth greens within 10 days of returning to a balanced feed.
- 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: ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md)

### Nickel deficiency (Less likely)

- Kind: Nutrient; urgency: Low urgency
- Fix: No published cannabis case. Only conceivable on very pure RO systems fed urea; do not add nickel otherwise (excess is toxic and cannabis accumulates metals).
- Recovery: Not applicable in practice; look for another cause.
- 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: [Nickel (Ni) in cannabis: essential, needed in traces, almost never worth adding](https://genetixbay.com/knowledge/nutrients/nickel.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.