Short answer
Nutrient burn is fertilizer toxicity. It starts as yellow or brown crispy tips on the leaves furthest up and closest to the light, then works backward along the leaf edge. It means the plant is being given more nutrient salts than it can use.
- What nutrient burn actually is
- How to identify nutrient burn
- Nutrient burn or deficiency? The differences that matter
- Other things that look like nutrient burn
- What causes it
- How to fix nutrient burn
- Does flushing actually work?
- How it differs by medium
- EC and ppm targets by stage
- What recovery actually looks like
- Preventing it
- Frequently asked questions
- The short version
The fix is to flush with pH corrected plain water until runoff EC drops close to your input, then resume feeding at roughly half strength. Damaged leaf tips never recover, so judge success by whether new growth comes in clean, not by whether the burn disappears.
What nutrient burn actually is
Nutrient burn is not a disease and not a deficiency. It is the plant sitting in a solution more concentrated than it can handle.
Roots take up water by osmosis, moving it from the lower salt concentration outside the root toward the higher concentration inside. When the surrounding solution becomes more concentrated than the root, that gradient weakens and can reverse, so the plant struggles to draw water at all. The extremities suffer first because they are furthest from the roots and transpire hardest. That is why the tips go first and the damage spreads inward along the leaf margin.
The practical implication is that nutrient burn is a concentration problem, not a specific nutrient problem. You do not need to identify which element is excessive. You need to lower the total salt load in the root zone.
How to identify nutrient burn
It follows a very consistent progression, which makes it one of the easier problems to diagnose confidently.
Stage 1: tip yellowing
The very tips of leaves turn yellow, often only a few millimetres. Easy to miss and easy to dismiss. Appears first on the upper canopy nearest the light, because those leaves transpire most and accumulate salts fastest.
Stage 2: tips brown and crisp
Yellow tips turn brown or bronze and go dry and brittle. They will crumble if you rub them. The affected area is clearly dead rather than discoloured.
Stage 3: damage moves along the margin
The burn spreads back from the tip along the outer edge of the leaf, forming a brown border while the center of the leaf stays green. Leaf tips may also curl or claw downward.
Stage 4: severe
Large portions of the leaf are brown and dead. Leaves drop. Growth slows or stops. In flower, bud development stalls and the plant may never recover its momentum.
The green center with a burnt margin is the signature. Very little else produces exactly that pattern.
Nutrient burn or deficiency? The differences that matter
This is the most consequential fork, because the treatments are opposites. Feed a burnt plant and you make it worse. Flush a hungry plant and you make it worse.
| Nutrient burn | Deficiency | |
|---|---|---|
| Where it starts | Upper canopy, nearest the light | Usually lower and older leaves first |
| Where on the leaf | Tips first, then inward along the margin | Often between veins, or the whole leaf |
| Texture | Dry, crispy, brittle, crumbles | Soft, pale, limp rather than crisp |
| Color | Brown or bronze, distinctly dead | Yellow, pale green, or spotted |
| Leaf center | Stays green while edges die | Often discolours across the whole leaf |
| Runoff EC | Higher than input | Lower than input |
| Treatment | Flush, then feed lighter | Feed more, or fix pH |
The runoff EC test settles it in about two minutes and removes all guesswork. Measure the EC or ppm of what you pour in, then measure what comes out of the bottom. Runoff meaningfully higher than input means salts are accumulating and you are looking at burn. Runoff lower than input means the plant is consuming faster than you are supplying, which is a feeding problem.
Other things that look like nutrient burn
| Problem | How to tell it apart |
|---|---|
| Light burn | Only on leaves closest to the lamp, often bleached or yellowed across the whole leaf rather than tip first. Moving the light or lowering intensity stops progression. |
| Heat stress | Leaf edges curl upward into a taco shape before browning. Follows temperature spikes, worst directly under the light. |
| Low humidity or high VPD | Whole margin crisps rather than starting at the tip. Plant may wilt during lights on and recover overnight. Check your VPD before touching the feed. |
| Wind burn | Affects only leaves in the direct path of a fan. Leaves look tattered or clawed as well as browned. |
| Excess cal-mag | Tip burn caused by overdosing a supplement people assume is harmless. See our cal-mag guide. |
What causes it
Following the bottle instead of the plant
Manufacturer feed charts are written to sell nutrients and are calculated for large, fast growing plants in ideal conditions. For most home growers those numbers are too strong. Many experienced growers run at half to three quarters of label strength and see no downside. Treat the chart as an upper bound, not an instruction.
Not measuring EC or ppm
Feeding by volume rather than by concentration means you have no idea what the plant is actually receiving. A meter is inexpensive and removes the guesswork entirely.
Stacking supplements
Base nutrients plus cal-mag plus a bloom booster plus an enzyme plus a root stimulant. Each label assumes it is the only thing being added. Together they can easily double the intended salt load. Read what is already in your base nutrient before adding anything alongside it.
Feeding seedlings and fresh clones like mature plants
A rooted cutting has minimal root mass and takes up very little. Full strength nutrients at that stage burn tips almost immediately. Start at a quarter strength and increase as roots establish.
Salt accumulation over time
Even a correct feed leaves residue behind. Without periodic plain water to carry it away, concentration in the medium climbs week after week until it crosses the threshold, which is why burn often appears suddenly on a schedule that had been working fine.
Letting the medium dry out too far
Water leaves, salts stay. As the medium dries, the remaining solution becomes more concentrated. Consistently dry pots produce burn at feed strengths that would otherwise be fine.
How to fix nutrient burn
- Stop feeding. No nutrients, no supplements, nothing but water until you have measured what is going on.
- Measure runoff EC or ppm to confirm the diagnosis and give yourself a baseline to flush against.
- Flush with pH corrected plain water. Roughly three times the container volume, so about three gallons through a one gallon pot. Pour slowly and let it drain fully.
- Test the runoff as you go. Stop when runoff EC is close to input EC. This is the actual endpoint, not a fixed number of gallons.
- Let the medium dry appropriately before watering again. A flushed pot left saturated invites root problems on top of the burn.
- Resume at half strength. Do not go straight back to the previous schedule, which is what caused the problem.
- Remove badly damaged leaves only if they are mostly dead. Leaves with green remaining are still photosynthesising and are worth keeping.
- Watch new growth for seven to ten days. Clean new growth means it is resolved.
Existing damage will not heal. Burnt tips stay burnt. This is the single most common source of confusion after a flush. The plant is not still burning, you are simply looking at old damage. Judge only by what emerges next.
Does flushing actually work?
Two different things get called flushing, and conflating them causes a lot of arguing at cross purposes.
Corrective flushing, which is what this page is about, means running plain water through the medium to physically remove accumulated salts. This is not controversial. It is straightforward chemistry, the same principle as fertilizer burn in any other crop, and you can watch it work on a meter as runoff EC falls. If you have burn, flushing fixes the cause.
Pre harvest flushing, withholding nutrients for one to two weeks before cutting to improve smoothness or taste, is genuinely disputed. The controlled work that exists has not shown reliable differences in blind assessment, and the plant cannot meaningfully purge minerals already built into its tissue. That does not make tapering pointless, since easing off feed late in flower is sensible for other reasons, but it is a different claim with far weaker evidence behind it. Do not let skepticism about the second kind stop you doing the first kind.
One caution on corrective flushing: do not do it out of habit. Running large volumes of plain water through a pot every week strips the nutrients the plant needs alongside the excess, and leaves the medium waterlogged. Flush to solve a measured problem, then go back to feeding.
How it differs by medium
The same feed strength behaves quite differently depending on what the roots are sitting in, which is why advice that works for one grower fails for another.
| Medium | Burn risk | What to know |
|---|---|---|
| Soil | Lower | Buffers well and holds a nutrient reserve, so problems build slowly and are slower to correct. Pre amended or "hot" soils already contain feed, and running a full schedule on top is a very common cause of burn in the first few weeks. |
| Coco coir | Moderate | Effectively inert with almost no buffer, so the plant experiences exactly what you give it. Burn appears fast but also clears fast. Frequent light feeding beats infrequent heavy feeding. |
| Hydroponics | Highest | No buffer at all and roots sit directly in solution. Burn can appear within hours. The upside is that a reservoir change fixes it almost immediately. |
| Living or organic soil | Lowest | Microbial life mediates nutrient release, so toxicity is uncommon. Bottled synthetic feeds can damage that biology, which is a different problem to manage. |
The general rule: the less buffering the medium provides, the more precisely you need to measure, and the faster both the problem and the fix arrive. See our soil vs coco vs hydro comparison for the wider trade-offs.
The underlying mechanism is identical in all four cases. Uptake depends on osmosis, and osmosis depends on the concentration gradient between the root and the solution around it. Buffering only changes how quickly that gradient moves against you.
EC and ppm targets by stage
These are conservative working ranges rather than maximums. Starting here and increasing if the plant asks for more is far safer than starting high.
| Stage | EC (mS/cm) | PPM (500 scale) | Notes |
|---|---|---|---|
| Fresh clones and seedlings | 0.4 to 0.8 | 200 to 400 | Minimal roots, minimal uptake |
| Early veg | 0.8 to 1.2 | 400 to 600 | Increase gradually |
| Late veg | 1.2 to 1.6 | 600 to 800 | Peak vegetative demand |
| Stretch and early flower | 1.4 to 1.8 | 700 to 900 | High growth rate |
| Mid flower | 1.6 to 2.0 | 800 to 1,000 | Usually peak of the whole cycle |
| Late flower | 1.2 to 1.6 | 600 to 800 | Taper down |
| Final week | 0 to 0.4 | 0 to 200 | Plain water if you flush |
Two caveats. PPM scales differ, so a meter on the 700 scale reads roughly 40 percent higher than one on the 500 scale for the same solution, and comparing numbers between growers without knowing the scale causes endless confusion. And you must add your source water EC to these figures. Tap water at 0.4 EC means a target of 1.6 requires only 1.2 of added nutrient.
What recovery actually looks like
Knowing the timeline stops people intervening again too early, which is how a manageable problem turns into a stalled plant.
| When | What you should see |
|---|---|
| Immediately after flushing | Nothing visibly different. Existing damage is permanent and the plant needs time. Resist the urge to add anything. |
| Day 1 to 3 | Progression stops. Tips that were spreading stop spreading. This is the first real signal it worked. |
| Day 3 to 7 | New growth emerges at the tops. Look at it closely. Clean, evenly green new leaves mean the problem is solved. |
| Day 7 to 14 | Growth rate returns to normal. Old damaged leaves stay damaged and some may yellow and drop, which is fine. |
| Beyond 14 days | If new growth is still coming in burnt, you have another cause. Check pH, source water, and whether a supplement is still in the mix. |
Two mistakes are common in this window. The first is flushing again after a few days because the old damage has not disappeared, which strips the nutrients the recovering plant now needs. The second is going straight back to the original feed schedule once new growth looks healthy, which simply restarts the cycle. Resume at half strength and climb slowly.
Timing matters for how much this costs you. Burn during vegetative growth is largely cosmetic, because the plant has time to outgrow it. Burn during mid flower is expensive, since the plant has limited time left to recover and every stalled day is bud development you do not get back.
Preventing it
- Buy an EC or ppm meter and use it on every mix and on runoff weekly. This one habit prevents most cases.
- Start at half the label rate and increase only if the plant looks hungry.
- Include plain water feeds periodically to carry residue away before it accumulates.
- Feed to a little runoff, around 10 to 20 percent, so excess salts leave the pot rather than concentrating in it.
- Check what is already in your base nutrient before stacking supplements on top.
- Scale feed to plant size, not to a calendar week. A small plant in week four does not need what a large plant in week four needs.
- Do not let pots dry out completely, which concentrates whatever is left behind.
Healthy, well rooted plants also tolerate feeding far better than struggling ones. Every clone we ship is rooted and established before it leaves, so it can take up nutrients properly from the start rather than sitting in solution it cannot use. You can browse the current strain list if you are planning a run.
Frequently asked questions
What does nutrient burn look like?
Yellow or brown crispy leaf tips that progress backward along the leaf edge, while the center of the leaf stays green. It appears first on upper leaves nearest the light and the damaged tissue is dry and brittle rather than soft.
Will nutrient burn kill my plant?
Rarely if caught early. Mild tip burn is cosmetic and the plant grows through it. Severe untreated burn stalls growth, drops leaves and can cost significant yield, particularly if it happens during flower.
Do burnt leaves recover?
No. Damaged tissue is dead and stays that way. Assess recovery by whether new growth comes in clean, typically within seven to ten days of flushing.
How much water do I flush with?
About three times the container volume, so roughly three gallons for a one gallon pot. The real endpoint is measured rather than counted: keep going until runoff EC is close to input EC.
Should I cut off burnt leaves?
Only if they are mostly dead. Leaves with green tissue remaining are still producing energy for the plant and should stay. Removing large numbers of leaves adds stress on top of the burn.
Can I get nutrient burn from cal-mag?
Yes. Cal-mag is widely treated as harmless and added by default, which makes it a common cause of tip burn. It also adds nitrogen via calcium nitrate, which matters in late flower.
What EC should I feed at?
Roughly 0.4 to 0.8 for clones and seedlings, 0.8 to 1.6 through veg, 1.6 to 2.0 at mid flower peak, tapering to 1.2 to 1.6 late. Add your source water EC to those figures, and confirm which ppm scale your meter uses.
Is nutrient burn the same as light burn?
No. Nutrient burn starts at leaf tips and moves along the margin, and appears wherever salts accumulate. Light burn affects only leaves closest to the lamp and usually bleaches or yellows the whole leaf rather than starting at the tip.
Recurring problems often trace back to weak or infected stock. Starting from verified, HLVd-tested clones removes a whole class of variables, and hardy beginner strains shrug off most early stress.
The short version
Crispy brown tips with a green leaf center, worst at the top of the plant, is nutrient burn. Measure runoff EC to confirm, flush with pH corrected plain water until runoff matches input, then resume at half strength.
Then buy a meter if you do not have one. Almost every case of nutrient burn is a measurement problem wearing a nutrient problem's clothes.
More from Troubleshooting
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- Why Are My Cannabis Buds So Small? 7 Common Causes
- Why Are My Cannabis Leaves Curling? Causes and Fixes
- Why Are My Clones Not Rooting or Growing?
- Cal-Mag Deficiency in Cannabis: Signs, Causes and Fixes
- Cannabis Foxtailing: What Causes It and How to Prevent It