Nutrient burn: brown tips and edges from too much feed

Timing is your best clue. If the tips started browning soon after you raised the feed strength, this moves up the list.

What it looks like

The signs growers know best are brown, crispy leaf tips and edges, which may then move inward. In greenhouse crops generally, very high salt levels can cause marginal leaf burn, wilting and slower growth (Purdue Extension).

What a surplus looks like depends on the nutrient. In a controlled study of a hemp cultivar, tenfold doses of manganese and boron both caused yellowing at the edges of lower leaves. It moved inward, and the edges eventually died. These took about 7 weeks to appear (Cockson et al. 2019). That’s a useful reminder that this kind of damage doesn’t always show up within days.

Why it happens

When plants use water faster than they use fertilizer, salts can concentrate in the mix. High salt levels reduce water uptake (Purdue Extension), so a plant can show drought-like symptoms even in a wet pot. Common triggers are stronger feed than the plant needs, feeding seedlings like mature plants, and pots that are rarely flushed through in systems that need it.

More feed isn’t automatically more growth. In one vegetative trial testing 30 to 320 mg/L of nitrogen, growth was best at 160, and impaired above and below it (Saloner & Bernstein 2020). Other trials and fertilizer types reached different numbers, so that isn’t a universal rate.

How to confirm it

1. Look back at what changed. Did you raise the strength or add a product just before it started?
2. Measure EC the same way each time. Record your input and use a consistent method on the mix. Ordinary runoff isn’t a standardized test, and a difference between input and runoff doesn’t prove a problem by itself. Our salt buildup guide explains how.
3. Compare with ranges for your method. Purdue’s table for greenhouse crops rates a PourThru reading of 6.6 to 7.8 mS/cm as very high, with salt injury possible (Purdue Extension). That’s a general greenhouse guide, not a tested limit for cannabis.
4. Watch new growth. Burnt tissue doesn’t heal, so old damage doesn’t tell you whether the problem is continuing.

What else it could be: this matters, because the fixes are opposites. Potassium deficiency also causes yellow, dying leaf edges on lower leaves (Cockson et al. 2019), and it needs more feed, not less. Heat, root problems and pH can look similar too. Dark green leaves don’t prove overfeeding: in the nitrogen trial, leaves were similarly dark from 160 to 320 mg/L (Saloner & Bernstein 2020).

What to do

1. Hold off on adding anything until you’ve measured.
2. If salts are confirmed high, lower the feed strength.
3. If you need to leach, use the right method for your setup. In a well-drained, top-watered pot, follow a procedure for that medium with suitable low-salt water or nutrient solution. Don’t pour large volumes through a waterlogged plant, a living-soil bed or a bottom-fed system. In coco, plain-water leaching isn’t a substitute for balanced feeding.
4. Remeasure the same way, then go back to a lower strength.
5. Remove leaves only if they’re dead, and judge the result on new growth.
6. Change one thing at a time. Stacking fixes makes it impossible to tell what worked.

How much to trust this

We didn’t find a controlled cannabis study that defines “nutrient burn” or sets a salt level at which tips burn. The term is grower language for several different things. The toxicity study used only one hemp cultivar in sand, with tenfold doses much higher than normal feeding mistakes, and described symptoms for just manganese and boron. The nitrogen trial measured growth, not tip burn. The salt ranges are for greenhouse crops in general, so measure, change one thing, and judge by new growth.