Nutrient Burn

Nutrient burn is salt damage. There is more dissolved fertilizer in the root zone than the plant can use, and the excess pulls water back out of the leaf tissue at the tips, where it is thinnest.

What you are seeing#

The newest, biggest, fastest growing leaves in the upper canopy. Fast growing tissue takes up the most water, so it takes up the most salt.

The very tip of each leaf blade goes yellow, then brown, then dry and crisp. The affected area is small at first, an eighth of an inch, and creeps back along the blade over days. Tips often hook downward.

The rest of the leaf stays a healthy, sometimes too dark green. That contrast between a lush dark leaf and a dead brown tip is the signature. In a serious case the burn spreads down the edges and the leaf curls under.

Lower and shaded leaves are affected later and less. A white crust on the soil surface or the pot rim confirms salt buildup.

Why it happens#

Nutrient labels are written for maximum growth under ideal conditions, which does not describe a first grow. Beginners then add supplements on top of a complete feed.

Common causes:

• Following the bottle at full strength.
• Feeding a seedling. Pre-amended soil holds three to five weeks of food and seedlings need nothing added.
• Stacking a Cal-Mag, a bloom booster and a base nutrient without adding up the total EC.
• Never watering to runoff, so salts accumulate week after week.
• Letting the medium dry too far, which concentrates the remaining solution.

How to fix it#

1. Stop feeding today. The next watering is plain pH-corrected water.
2. In coco or hydro, flush with 3 pot volumes of pH-corrected water. Get runoff EC under 1.2, about 600 ppm on the 500 scale.
3. In soil, water heavily to runoff once. Do not flush soil repeatedly, because a root ball saturated for days causes root rot, which is worse.
4. Resume feeding after one or two plain waterings at half your previous strength. Beginners should live around EC 1.0 to 1.4 in veg and 1.4 to 1.8 in flower.
5. Over the next week, measure total feed EC with a cheap meter instead of counting milliliters. Add up everything in the jug, not just the base nutrient.
6. Water to 15 to 20 percent runoff so salts leave the pot instead of stacking up.

How to tell it apart#

Versus light burn. Both burn the top of the plant. Light burn is positional: only leaves directly under the lamp are hit, and a leaf four inches to the side in the shade is clean. Nutrient burn affects every fast growing leaf regardless of how hard it is lit. If the pattern follows the lamp footprint, it is light.

Versus nitrogen toxicity. Nitrogen toxicity changes the whole leaf: dark blue-green, glossy, clawed under. Nutrient burn leaves the color mostly normal and kills only the tips. If the whole leaf went wrong, it is nitrogen specifically.

Versus potassium deficiency. This is the reversal that matters. Potassium deficiency also browns leaf edges, but it starts on the oldest lower leaves and burns the entire outer margin with rusty spots inside the green. Nutrient burn starts on the newest top leaves and takes only the tips. Bottom up is a deficiency, top down is an excess.

Versus heat stress. Heat also browns tips at the top, but it curls leaf edges upward into a taco and the canopy droops in the afternoon. Check canopy temperature before blaming the feed.

How long until it looks better#

The crisped tips are dead and stay that way. Do not strip the leaves off, because the rest of each blade is still working.

The useful measure is whether the burn is still advancing. After a flush and a reduced feed, the brown should stop creeping within three to five days, and new leaves opening after about a week should be clean to the tip. If fresh growth is still burning ten days later, your EC is too high or your runoff has nowhere to go.