Nutrient burn is the browning of leaf tips and edges that appears when the fertilizer in the root zone is stronger than the roots can handle. It is caused by the total concentration of dissolved fertilizer salts, not by one particular nutrient being poisonous by itself. Too much salt around the roots damages them and cuts water uptake, and some of it collects in the leaves, where the tips dry out first. The fix is to lower the feeding strength and flush the excess salt out of the medium with plain water.
What causes nutrient burn
Washington State University’s extension service puts it plainly: excessive use of fertilizers can damage or kill plants. High salt levels in the root zone damage roots and reduce water uptake, and salts can accumulate in leaf tissue, killing the tips and margins. Penn State calls the root-zone side of this “chemical-induced drought”: the medium is wet, but the plant behaves as if it is dry.
Common triggers:
- Feeding at full label strength every watering, especially on young plants.
- Adding several supplements on top of a complete base nutrient.
- Small containers. WSU notes that container plants are particularly susceptible to fertilizer damage.
- Hydroponics and coco. Penn State describes hydroponic systems as less forgiving than soil, with symptoms appearing quickly.
- Letting the medium dry hard between feeds, so the remaining salts become more concentrated.
Seedlings and fresh clones burn most easily. A Vietnamese grower handbook advises starting seedlings in a small pot of mild, humus-rich mix with only a little organic nitrogen, to avoid excess nutrients that lead to leaf burn and slowed growth.
What nutrient burn looks like
The University of Maryland Extension lists the typical symptoms as browning or dieback of the leaf tips and margins. Other signs can include reduced growth, lower leaf drop, dead root tips and wilting. A white crust of fertilizer salt may form on the surface of the medium or on the outside of pots.
In cannabis, the first sign is usually the very tips of the leaflets turning yellow-brown and dry. If feeding continues, the brown moves inward along the edges. Heavily fed plants often have very dark green leaves as well. The same handbook notes that excess nitrogen makes leaves unusually dark green, and that leaf edges can curl downward, much like overwatering. Excess nitrogen does not always cause burnt tips, though.
WSU gives a useful diagnostic clue: unlike many disease and insect problems, fertilizer burn symptoms are typically evenly distributed on the plant.
Which leaves show it first
Nutrient burn does not follow the old-leaf versus new-leaf rule used for deficiencies. It shows up as tip and edge damage spread fairly evenly over the plant, not as a problem that starts on one age of leaf.
Deficiencies are different. Nutrients that the plant can move (mobile nutrients) are pulled out of old leaves to feed new growth, so symptoms appear on older leaves first. Immobile nutrients cannot be moved, so symptoms appear on new growth first. The University of Delaware lists nitrogen, phosphorus, potassium and magnesium as mobile, and calcium, copper, boron, iron, manganese and zinc as immobile.
How to tell nutrient burn from similar problems
| Problem | Where it starts | What it looks like | Typical history |
|---|---|---|---|
| Nutrient burn | Leaf tips, then edges, spread evenly over the plant | Brown, dry, crispy tips; rest of the leaf often dark green | Feed strength recently raised; salt crust on the medium |
| Deficiency | Old leaves (mobile nutrients) or new leaves (immobile nutrients) | Yellowing, pale or patchy color, slow growth | Light feeding, heavy leaching, or a long time in the same medium |
| Lockout | Deficiency pattern, often several at once | Deficiency signs, sometimes with burnt tips as well | Plant is fed well, but pH is off or salts have built up |
| Heat or light stress | Top of the canopy, closest to the lamp or sun | Bleached, yellowed or scorched upper leaves; lower leaves fine | Lamp too close, hot room, or plants moved suddenly into strong sun |
Two quick checks help. First, look at the pattern: burn is spread over the plant, while heat and light damage are concentrated at the top. Second, think back: if the trouble started after you increased the feed, burn is the most likely answer. Virginia Tech’s diagnostic guide notes that a rapid change from low to high light destroys leaf chlorophyll, causing yellowing and necrosis, the equivalent of sunburn.
How to fix nutrient burn
- Lower the feeding strength. Go back to a clearly lower dose than the one that caused the damage. WSU’s advice is to fertilize moderately according to the needs of the plant.
- Leach the container. WSU recommends watering heavily and letting the water drain away from the pot to remove some of the salts. The University of Maryland suggests repeating several irrigations, each with a volume of water at least equal to the pot size. The Vietnamese handbook describes a heavier soil flush of 3 to 10 times the pot volume, followed by pH-adjusted water.
- Replace the medium if needed. For small pots with very high salt levels, the University of Maryland advises replacing the growing medium instead of flushing.
- Measure, do not guess. Purdue University describes electrical conductivity (EC) as a measure of the dissolved salt concentration in the growing medium. Measuring the EC of your feed and your runoff tells you whether salts are building up.
- Judge progress by new growth. Brown tips do not turn green again. If the new leaves come out clean, the problem is solved. Trim badly damaged leaves only if they are dying.
Note that leaching only helps with quick-release and liquid fertilizers, as WSU points out. Slow-release pellets mixed into the medium will keep releasing salts.
Common mistakes
- Treating burn as a deficiency. Brown tips are read as hunger, more fertilizer is added, and the damage speeds up.
- Feeding a stressed plant. WSU says never to apply fertilizer to plants stressed by heat or drought. In a hot tropical grow room or on a sun-baked balcony, water first and feed later.
- Stacking supplements. Each bottle adds salt, even if each is used at its label rate.
- Assuming lush growth is healthy growth. WSU also notes that aphids, mites and other pests often thrive on the soft growth produced by heavy fertilization.
- Measuring only what goes in. The feed can be correct while the medium has been accumulating salt for weeks. Check the runoff too.
Slight tip burn that stops spreading once you lower the feed is not a crisis. Burn that climbs up the leaves week after week, or that appears in seedlings, means the feed is too strong for that plant at that stage.