# New growth evenly pale or yellow: likely causes and fixes

> New growth evenly pale or yellow on cannabis is most often High root-zone pH locking out iron, manganese, zinc, boron and copper, Aphids or Sulfur deficiency. How to tell them apart, the fix for each and what recovery looks like.

Also called: top leaves yellow, new leaves coming in yellow, yellow tops, pale new growth, new growth lime.

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

## Likely causes, most likely first

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

- 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)

### Aphids (Less likely)

- Kind: Pest; urgency: Deal with it this week
- Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them.
- Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks.
- 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: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby.
- Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md)

### Sulfur deficiency (Less likely)

- Kind: Nutrient; urgency: Low urgency
- Fix: Rare unless a feed is built only from nitrates and chlorides. Supply about 50-120 mg/L S as sulfate, e.g. via magnesium sulfate or potassium sulfate at normal rates.
- Recovery: New leaves emerge green within 7-10 days.
- 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.
- Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little.
- 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: [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md)

### Iron deficiency (usually high pH) (Less likely)

- Kind: Nutrient; urgency: Low urgency
- Fix: Bring root-zone pH into range first: soilless 5.5-6.2, soil 6.0-6.8. Neutralise alkaline water with acid. Supply 1.5-3 mg/L Fe as a chelate matched to pH: EDTA to about pH 6.5, DTPA to about 7.5, EDDHA to about 9. A foliar iron chelate spray (veg only) greens leaves in days.
- Recovery: The next new leaves open green within 5-10 days; the whitened leaves re-green partly or not at all.
- 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: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little.
- 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: [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md)

### Plant virus (e.g. beet curly top, lettuce chlorosis virus) (Less likely)

- Kind: Disease; urgency: Deal with it this week
- Fix: No cure: remove the plant. Control insect vectors (leafhoppers outdoors for curly top; whiteflies for some others) and test clone sources.
- Recovery: No new symptomatic plants over the next 2-4 weeks.
- Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks.
- 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.
- Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.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.