Cannabis nutrient burn solution: flush the pot, then feed at half strength
Nutrient burn is salt damage from a feed mix above what the root zone can take. Signs: brown tips on top leaves, dark green leaves that curl down, crisp leaf edges, slow growth. The fix: stop all nutrients, run pH 6.0 to 6.5 water through the pot at 2 to 3 times the pot volume, wait 5 to 7 days, then resume at 50% of the last dose.
Step 1: Confirm nutrient burn
Check the last feed EC or ppm. Nutrient burn shows on the top and middle leaves first. Tip burn on lower leaves points to a different problem, such as dry soil or salt buildup from tap water. Measure runoff EC. Runoff more than 300 ppm above the input confirms salt buildup in the root zone.
Step 2: Flush the root zone
Use 2 to 3 times the pot volume. A 5 gallon pot takes 10 to 15 gallons of water. Set water pH to 6.0 to 6.5 in soil, 5.8 to 6.2 in coco. Keep water at 65 to 70 F. Pour slow, in 1 gallon parts, and let each part drain. Stop when runoff EC is within 300 ppm of the input water.
Step 3: Reset the feed
Wait 5 to 7 days. Water with pH-adjusted water and no nutrients. Resume at 50% of the last nutrient dose. Raise the dose by 10% per week. Keep runoff EC within 300 ppm of the input EC. Feed until 10 to 20% runoff leaves the pot.
Step 4: Remove dead tissue
Leave brown tips on the plant. They show the damage line and do not spread once the feed is fixed. Remove leaves that are brown or crisp. Do not remove more than 20% of fan leaves in one session.
Recovery timeline
New growth appears in 5 to 10 days. Burned tips stay brown. Leaf color on new leaves returns to green in 2 to 3 weeks. Flower yield loss stays under 10% when the flush starts within 3 days of the first tip burn.
What not to do
- Do not add more calmag or bloom booster to fix tip burn.
- Do not flush with tap water above 200 ppm.
- Do not feed again at full strength in the same week.
- Do not run a flush in the last 14 days of flower.