Short answer
Nutrient burn is salt damage in the root zone. The first sign is a crisp brown or bronze tip on a dark green leaf. Stop feeding. Run water or a weak nutrient solution through the pot until runoff EC drops near input EC. Wait 5 to 10 days. Refed at 50 to 75 percent of the old rate. Damaged leaves stay damaged. Judge recovery by new growth, not by old leaves.
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1. Confirm burn before you change anything
- Burn: tips turn brown and crisp first, then damage moves inward. Leaf color stays dark green.
- Nitrogen excess: leaves claw downward, stems stay soft, flower sites stall.
- Deficiency: yellow starts between veins or on old lower leaves, and the tips stay green.
- Measure pH and EC of the feed and of the runoff. Two numbers tell you where the problem sits.
2. Flush the root zone
Soil: run water at pH 6.0 to 6.8 through the pot. Use 2 to 3 times the pot volume. A 5 gallon pot takes 10 to 15 gallons. Coco and hydro: do not use plain water. Run a weak nutrient solution at 25 to 50 percent of your normal EC. Stop when runoff EC is within 0.2 to 0.3 mS/cm of input EC.
3. Refeed
Wait 1 to 2 days after the flush. Mix at half the strength you used before the burn. Raise the rate by 10 percent every 3 days if new tips stay green. Hold the pH at 5.8 to 6.2 in coco and hydro, 6.0 to 6.8 in soil.
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4. Fix the cause
- Feed schedule ahead of plant demand, or reuse of drain water without a check.
- Salt buildup in reused media. Test runoff at every third feeding.
- Additive stacking. Base nutrients plus three boosters often push EC past 2.5 mS/cm.
- Root zone above 75 F. Warm solution moves into the plant faster.
- Autoflowers and young clones burn at lower rates than photoperiod plants in week 5 of flower.
5. Target numbers
- Veg feed: 1.0 to 1.6 mS/cm.
- Flower feed: 1.4 to 2.2 mS/cm.
- Runoff: within 200 to 300 PPM of input.
- Root zone: 65 to 75 F.
6. Timeline
Day 0: flush. Day 1 to 3: expect droop from wet media. Day 4 to 7: new growth at the top should show even color. Day 7 to 14: return to a normal feed rate. Remove burned leaves only if they block light or trap moisture against buds. The plant will not repair them. No published trial sets a recovery rate for cannabis, so treat these counts as grower practice, not research data.