Français Scorched, yellow or crispy leaves are easy to blame on the wrong cause. Light burn and nutrient burn are two of the most common culprits, and they call for opposite fixes: one means moving the lamp, the other means feeding less. The quickest way to tell them apart is to look at where on the plant the damage appears.
Diagnosis
Look at where the damage is
Light burn hits the top of the plant. Nutrient burn usually starts at the leaf tips.
Autoflower seeds
How to tell them apart
| Clue | Light burn | Nutrient burn |
|---|---|---|
| Where | Top of the plant, closest to the lamp | Often the whole plant, starting at the leaf tips |
| Colour | Bleached yellow or white patches | Yellow, then brown and crispy tips; leaves are often very dark green first |
| Leaf shape | Edges may curl up like a taco | Tips may curl down like a claw |
| Buds | Pale or bleached tops | Usually unaffected until the problem is severe |
| Quick test | The back of your hand feels hot at canopy height | Feeding strength or EC has recently gone up |
Fix it
Change one thing at a time so that you know what worked. Burned tissue does not turn green again, but new growth will come in healthy once the cause is fixed.
Fixes
Two different remedies
Light burn
Give the plant more space
Raise or dim the lamp until the back of your hand is comfortable at canopy height after about 30 seconds. Keep the space cool with moving air.
Nutrient burn
Feed less and check pH
Cut the feeding strength by a quarter to a half. If the tips are scorched, rinse the medium with plain, pH-adjusted water, then build the feed back up slowly.
Lamp distance depends on the type and power of the light, so start from the manufacturer’s guidance and read our guide to choosing grow lights. Heat adds to the problem, so keep the grow room within the ranges in our notes on temperature and humidity.
Check pH and feeding strength
A pH that is off can lock nutrients out and produce symptoms that look like burn or deficiency even when the feed is correct. As a rough guide, aim for about 6.0–7.0 in soil and 5.5–6.5 in coco or hydro. Autoflowers are particularly sensitive to strong feeding, and our autoflower nutrient guide covers NPK, EC and growing media. If the symptoms do not match either burn, compare them with the different types of cannabis deficiencies.
Prevention
Habits that avoid both problems
Common questions
How far should grow lights be from cannabis? It depends on the light type and power. Follow the manufacturer’s guidance, then use the hand test at canopy height: if the back of your hand feels hot after about 30 seconds, raise or dim the light.
Will burned leaves turn green again? No. Damaged tissue stays damaged, but new growth will be healthy once you fix the cause. You can trim fully dead leaves later.
Can LED lights cause light burn? Yes. Strong LEDs can bleach leaves and buds if they are too close or set too high, even though they run cooler than older lamps.
What pH should I use? Roughly 6.0–7.0 in soil and 5.5–6.5 in coco or hydro. A wrong pH can cause deficiency-like symptoms even when the feeding is right.
Is it nutrient burn or a deficiency? Burn usually starts at the leaf tips and appears after feeding has been increased. Deficiencies tend to show as pale or mottled leaves. Check your feeding history and pH first.
