Cannabis Nutrients — Spot Deficiencies & Toxicities

Spotting cannabis deficiencies — the key to healthy plants

Spotting cannabis deficiencies is the biggest hurdle for most home growers — not because the symptoms are rare, but because many nutrient deficiencies look confusingly alike at first glance. Yellow leaves can mean nitrogen deficiency, but they can just as easily come from the wrong pH or plain overwatering — if the yellowing shows up specifically during flowering, check out our guide to yellow leaves in the flowering stage. If you start feeding blindly, you often just make the real problem worse. This hub brings together every nutrient deficiency and toxicity in cannabis in one place — a system instead of guesswork.

Cannabis needs three groups of nutrients: macronutrients (nitrogen, phosphorus, potassium) in large amounts, secondary nutrients (calcium, magnesium, sulfur) in moderate amounts and micronutrients (iron, manganese, zinc and others) only in trace amounts. If one of them is missing or present in excess, the plant shows it through discoloration, deformed growth or burnt leaf edges.

The most reliable way to identify a deficiency isn’t the symptom alone, but where it appears on the plant. When mobile nutrients such as nitrogen, phosphorus and magnesium run short, the plant moves them from old leaves to new ones — so the symptoms show up at the bottom first. Immobile nutrients such as iron, calcium and sulfur, on the other hand, stay put: here, deficiencies show up first on the youngest, topmost leaves. This rule of thumb alone rules out half of all candidates before you even get into the details.

It’s just as important to tell a deficiency from a toxicity — ironically, both can cause similar symptoms but call for opposite fixes. Burnt leaf tips that claw downward almost always point to nutrient burn, while pale, evenly bleached leaves are more likely a true deficiency. Further down you’ll find both categories neatly separated: one tab for deficiencies, one for toxicities.

Before you add more nutrients, it almost always pays to check the pH of your growing medium first: roughly 90% of all supposed nutrient deficiencies are really pH lockout, where the roots simply can’t take up nutrients even though there’s enough available. Use our free Plant Diagnosis Tool to narrow down your specific symptom in just a few questions, or take a look at our complete deficiency overview with a quick diagnosis table covering all 11 deficiencies at a glance.