Leaf Tip Burn in Cannabis: Causes and Prevention
Discover the common causes of leaf tip burn in cannabis and learn how to prevent it.
Answer first
Flush when nutrient burn is severe. Mild tip burn does not need a flush. Cut feed strength by 20 to 30 percent and check runoff EC. Severe burn shows burnt edges on many leaves, clawing, and dark green color. Then flush with 2 to 3 times the pot volume of pH-adjusted water. Resume feed at 50 percent strength.
What nutrient burn looks like
Nutrient burn comes from a root zone with too much salt. Leaf tips turn brown and crisp. Edges curl down. Leaves look dark green. Signs start at the top of the plant and move down.
Does Nutrient Burn Stop Plant Growth? Signs and Recovery
Check runoff EC before you act. Runoff EC more than 0.5 mS/cm above input points to salt buildup. A pH meter reading outside 5.8 to 6.2 in coco, or 6.0 to 6.5 in soil, points to lockout, not burn.
does nutrient burn stop plant growth
When not to flush
- One or two burned tips on older leaves. Lower feed by 20 percent. No flush.
- Burn from a single hot feed. Skip one feeding. Water to runoff. No flush.
- Late flower. Flushing stops feed during bud swell. Fix the feed rate first.
How to flush for nutrient burn
- Mix water at pH 6.0 to 6.5 for soil. Use pH 5.8 to 6.2 for coco. Let tap water sit 12 to 24 hours if chlorine is high.
- Pour 2 times the pot volume through the medium. For a 5 gallon pot, use 10 gallons of water.
- Use 3 times the pot volume for severe burn. That is 15 gallons for a 5 gallon pot.
- Measure runoff EC at the end. Stop when runoff EC is within 0.3 mS/cm of the input water.
- Feed at 50 percent strength 1 to 2 days after the flush.
Soil
Soil holds salts longer. Use 3 times the pot volume. Let the pot drain. Do not let the pot sit in runoff.
best ph for cannabis nutrient uptake
Coco
Coco drains fast. Use 2 times the pot volume. Check runoff EC. Coco can need a second flush 3 days later.
Hydro
Drain the reservoir. Refill with pH-adjusted water at 25 percent strength nutrient. Run the system 30 minutes. Dump and refill at 50 percent strength.
After the flush
Wait 2 days. Look at new growth. New leaves should come out flat and green. Old burned tips will not heal. That is normal. Raise feed by 10 percent each week until runoff EC stays within 0.3 mS/cm of input.
Do not flush more than once in 7 days. Repeated flushing removes oxygen from the root zone and slows growth.
What not to do
- Do not flush with plain water for more than 24 hours in hydro.
- Do not use a flush product as a fix for pH lockout. Fix pH first.
- Do not flush in the last 2 weeks of flower unless burn is severe.