Nutrient Deficiency vs. Nutrient Burn: How to Tell the Difference

Your plant looked fine two days ago. Now the leaves are yellowing, browning, or developing spots — and you're not sure whether to feed it more or flush it out.

Getting this wrong makes things worse. Adding nutrients to a plant with burn deepens the problem. Flushing a genuinely deficient plant strips away what it needs. So before you do anything, you need to know which one you're actually dealing with.

Here's how to tell them apart.

The Key Visual Difference: Where Symptoms Start

This is the fastest diagnostic in cultivation:

Nutrient burn always starts at the leaf tips. Look at the very ends of your leaves. If you see yellowing, browning, or crisping that begins at the tip and works inward, you're looking at burn. The tips may curl down slightly and feel dry or papery.

Deficiencies rarely start at the tips. They typically appear in the middle or across the whole leaf, often with distinct patterns depending on which nutrient is missing. The exception is potassium (K), which can brown at edges and tips — which is why the next step always matters.

If you can identify where the symptom starts, you've narrowed it down to one or the other.

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Check pH Before You Do Anything Else

Here's the most common mistake: assuming symptoms mean the plant needs more nutrients, when the real problem is pH lockout — the plant literally cannot absorb nutrients that are already in the medium.

Cannabis is particular about pH. When the root zone pH is off, specific nutrient uptake shuts down, and the plant shows what looks exactly like deficiency symptoms. The nutrients are there. The plant just can't use them.

Target pH ranges:

Soil: 6.0–7.0 (sweet spot around 6.5)
Coco coir: 5.8–6.2
Hydro / DWC: 5.5–6.0

Test your runoff pH, not just your input water. Runoff tells you what's actually happening in the root zone. If your runoff is outside the target range, correct pH first — before changing your nutrient program. Nine times out of ten, the "deficiency" resolves within a week.

What Deficiency Looks Like (By Nutrient)

Once you've confirmed pH is in range, you can start identifying which nutrient is causing the problem. The pattern and location of discoloration are your clues.

Nitrogen (N) deficiency — the most common. Lower/older leaves turn solid yellow, starting from the tip and progressing to the whole leaf. The plant moves nitrogen upward to support new growth, so symptoms always show on the oldest leaves first. Stems may also look pale.

Phosphorus (P) deficiency — leaves darken to deep green or develop purple/red tones, especially on undersides. Usually starts on lower leaves. More common in cold root zones (below ~60°F).

Potassium (K) deficiency — edges and tips yellow or brown, starting on older leaves. Looks similar to burn, which is why pH check comes first. Leaves may also show upward curl.

Magnesium (Mg) deficiency — interveinal chlorosis: the areas between veins turn yellow while the veins themselves stay green. Starts on middle or lower leaves. Classic in coco coir grows.

Calcium (Ca) deficiency — new growth is affected (immobile nutrient). Brown spots, distorted or claw-like new leaves, tip curl on the youngest growth. Often appears alongside Mg deficiency.

What Burn Looks Like

Nutrient burn is simpler to identify visually. The sequence is:

Tips lighten to yellow
Tips turn brown, dry, and papery
Brown area grows inward from the tip
In severe cases, leaves curl down and the whole outer edge is affected

The key: your feeding was recently increased, or you're feeding at high concentrations. The plant is processing more nutrient salts than it can use. The excess accumulates at the leaf tips, which is where water transpires — and where the salt concentration becomes toxic.

If you recently bumped your feed strength or switched to a stronger formula, and symptoms appeared within a few days, it's almost certainly burn.

What to Do Right Now

Follow this order — don't skip steps.

Check runoff pH. If it's outside your target range, this is the root cause. Flush with pH-corrected water and wait 48–72 hours before reassessing.
If pH is correct, check your recent feeding history. Did you increase dosage? Switch products? Start feeding earlier in the cycle than intended? If yes → burn is the likely cause.
For burn: Reduce feed strength by 25–50%. If tips are heavily browned and progression is fast, flush with plain pH-corrected water (2–3× pot volume), then resume feeding at half strength.
For deficiency (pH confirmed correct): Add a targeted supplement. For N: any nitrogen-dominant veg feed. For Mg: Epsom salt (1 tsp/gallon) or a Cal-Mag supplement. For Ca and Mg together: Cal-Mag is the standard fix. For K: a bloom booster or potassium-specific additive.
Don't chase symptoms in late flower. Lower leaf yellowing in the final 2–4 weeks of flower is normal — the plant is cannibalizing nitrogen from fan leaves to fuel bud development. Don't add nitrogen during this window.

How to Know It's Working

Burn: existing damage won't reverse — browned tips stay brown. But new growth should come in clean within 5–7 days of correcting the feed. If new growth also shows tip burn, your correction wasn't enough.

Deficiency: mobile nutrients (N, P, K, Mg) won't restore the affected leaves, but symptoms stop spreading to new growth within 5–10 days of correction. Immobile nutrient deficiencies (Ca, Fe) show improvement on new growth first.

If symptoms keep spreading after a week of correction, reassess pH again. Persistent symptoms despite correct pH and reasonable feeding almost always point to a root zone issue (overwatering, root rot, or pH stratification in the medium).