Nutrient burn, salt buildup and runoff pH

When plants use water faster than they use fertilizer, salts concentrate in the medium. Leaf tips burn, and pH can swing.

Reading the signs

• Yellow or brown tips can come from excess salts, but also from other stresses. Check your measurements and recent changes.
• Marginal burn can indicate salt stress, but root problems, heat and nutrient deficiencies can look similar.

Reset the pot

1. Confirm the problem first. Use a consistent extraction method that suits the medium, and compare with guidance for that method and your previous readings. Record input EC separately; a difference alone doesn’t prove toxic buildup.
2. If excess substrate salts are confirmed in a well-drained, top-watered pot, follow a leaching procedure for that medium, using suitable low-salt water or nutrient solution. Don’t automatically pour one or two pot volumes through a waterlogged plant, a living-soil bed or a bottom-fed system. Let it drain and retest the same way.
3. In coco, account for the base fertilizer, water composition and buffering state. Repeated plain-water leaching isn’t a substitute for a balanced program.
4. Then go back to feeding at a lower strength.

About runoff pH

Runoff pH is often different from your input, and that’s normal. Ordinary runoff isn’t a standardized root-zone test. A 2025 hemp study found growth suppression below about pH 5.0 in peat-based substrate, but it didn’t establish one target for every medium. Confirm persistent shifts, check water alkalinity and fertilizer chemistry, and use corrections that suit your system instead of extreme-pH drenches.

Damage is permanent

Burnt tissue doesn’t turn green again. Judge recovery by new growth.