Nutrient Deficiency Guide: Identify & Fix Every Deficiency Fast
Visual symptom guide for cannabis, tomatoes, and all hydroponic crops — with exact product fixes
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Nutrient deficiencies are the #1 cause of stunted growth and failed harvests. The tricky part: many deficiencies look identical at first glance — yellowing leaves could be nitrogen, sulfur, iron, or even a pH lockout. This guide breaks down every major deficiency by leaf symptoms, affected plant part, and fastest fix.
⚠️ Check pH First — Always Before buying supplements, check your root-zone pH. 90% of "deficiencies" are actually pH lockout — nutrients present but unavailable. Soil: 6.0–7.0. Coco/Hydro: 5.5–6.5.
Macronutrient Deficiencies
🟡 Nitrogen (N)
Lower leaves yellow first, moves up. Overall pale green. Most common deficiency — especially in late veg.
🟠 Phosphorus (P)
Purple/red stems and undersides of lower leaves. Dark green upper leaves. Slow growth in flower.
🟤 Potassium (K)
Brown burned leaf edges, especially tips. Starts at lower leaves. Common in mid-to-late flower.
🟡 Calcium (Ca)
New growth distorted, brown spots on upper leaves. Blossom end rot in tomatoes. Fix with Cal-Mag.
🟡 Magnesium (Mg)
Interveinal chlorosis on older leaves — yellow between green veins. Very common in coco and hydro.
🟡 Sulfur (S)
New growth yellows from top. Similar to N deficiency but affects newest leaves first, not oldest.
Micronutrient Deficiencies
⚪ Iron (Fe)
New growth bright yellow with green veins. Most common when pH too high (above 7.0 in soil).
🟤 Manganese (Mn)
Interveinal chlorosis on newer leaves — very similar to iron. Check pH and water source.
🟡 Zinc (Zn)
Small new leaves, interveinal yellowing, leaves twist. Often seen in high-pH environments.
🟠 Boron (B)
Thick hollow stems, new growth brown and crinkled. Rare but more common in RO water grows.
🟤 Copper (Cu)
Leaf tips bluish-green then tan/brown. Iridescent sheen. Very rare in properly maintained grows.
🟡 Molybdenum (Mo)
Cupping of middle-aged leaves, pale yellow margins. Most common in acidic soil below pH 6.0.
Step-by-Step: How to Diagnose Any Deficiency
1
Check pH of root zone — Get a calibrated pH meter (Bluelab recommended). Flush if pH is off. Do this before anything else.
2
Identify which leaves are affected — Lower/older = mobile nutrient (N, P, K, Mg). Upper/newer = immobile nutrient (Ca, Fe, Mn, Zn).
3
Check runoff EC — Too high means salt buildup blocking uptake. Flush with plain pH water if EC over 3.5.
4
Match to symptom — Use the grids above. When in doubt, a full-spectrum base nutrient fix at proper pH resolves 80% of cases.
5
Apply targeted fix — Cal-Mag for calcium/magnesium, foliar spray works in 24–48 hrs for micronutrients.
Recommended Products
General Hydroponics CALiMAGic
Best Cal-Mag for coco and hydro — prevents most deficiencies proactively
From $14Shop NowBluelab pH Pen
The industry standard — accurate to ±0.1, waterproof, essential tool
From $79Shop NowGeneral Hydroponics Flora Series (3-Part)
Complete macro + micronutrient profile — adjustable N-P-K ratios
From $29Shop Now
Frequently Asked Questions
Why are my cannabis leaves turning yellow?
Yellowing most commonly indicates nitrogen deficiency, pH lockout, overwatering, or natural senescence near harvest. Check pH first (should be 6.0–7.0 in soil, 5.5–6.5 in coco/hydro). If pH is correct, add nitrogen-rich nutrients like GH FloraGro or Athena Grow.
How do I tell the difference between nitrogen and sulfur deficiency?
Nitrogen deficiency starts at the oldest, lowest leaves and moves upward. Sulfur deficiency starts at the newest growth at the top. If your newest leaves are yellowing first, it is sulfur — if the bottom is going yellow and moving up, it is nitrogen.
What is Cal-Mag and do I need it?
Cal-Mag supplements are calcium and magnesium — two nutrients that are often depleted in coco coir and RO water grows. If you grow in coco or use reverse osmosis water, Cal-Mag should be used on every watering. General Hydroponics CALiMAGic and Botanicare Cal-Mag Plus are popular choices.
Can I fix deficiencies with foliar spray?
Yes — foliar feeding delivers nutrients directly through leaves and works within 24–48 hours for micronutrients (iron, manganese, zinc). It is a fast emergency fix but does not replace correcting root-zone pH and nutrient solution. Always spray during lights-off to avoid leaf burn.
