Cannabis Nutrient Problems: Identify and Fix Every Deficiency and Excess

Yellowing, browning, curling, spotting: nutrient problems show up on the leaves before they show up in your yield. This guide walks through every common deficiency and excess by symptom, plus the pH lockout that mimics both, so you can diagnose what you’re looking at and fix it today. If you haven’t got a feeding schedule dialed in yet, start with our cannabis nutrients guide first, this page is for troubleshooting a plant that’s already showing symptoms.

Deficiency or Excess? Tell Them Apart First

Deficiencies typically start on the lower, older leaves and work upward as the plant reallocates what little it has. Excess shows up differently: burnt, curling tips on otherwise dark, healthy-looking leaves, often across the whole plant at once. Before treating either, check your pH. A reading outside 6.0-7.0 can lock out nutrients that are actually present in the soil, producing deficiency symptoms even when your feeding is correct, see the pH section below before you change your feed.

Primary Macronutrient (NPK) Deficiencies

• Nitrogen: pale, yellowing lower leaves that drop as it progresses, weak overall growth. Fix: increase nitrogen gradually in a grow-stage formula, don’t jump straight to full strength.
• Phosphorus: dark green leaves with a bluish tint, purple stems or leaf undersides, stunted growth, delayed or poorly developed buds. Fix: switch to a bloom-heavy formula and confirm pH, phosphorus lockout is common below 6.0.
• Potassium: yellowing or browning leaf edges starting at the tips, leaves turning crispy, reduced overall vigor. Fix: increase potassium-heavy feeding and check for calcium or magnesium overapplication, both can block potassium uptake.

Primary Macronutrient Excess

• Nitrogen excess: unusually dark, lush foliage, but delayed flowering and reduced bud development. Fix: cut nitrogen immediately, especially if you’re still feeding a veg formula into flower.
• Phosphorus excess: blocks iron and zinc uptake, causing secondary deficiency symptoms. Fix: flush with plain, pH-balanced water and reduce feed strength.
• Potassium excess: blocks calcium uptake, weakening cell structure. Fix: flush and dial back concentration, then reintroduce at a lower strength.

Secondary Macronutrient and Micronutrient Deficiencies

• Calcium: curling or cupping new growth. Our calcium deficiency guide covers this one in more depth, it’s common enough to deserve its own page.
• Magnesium: yellowing between the veins on older leaves first (interveinal chlorosis), veins stay green.
• Sulfur: overall yellowing similar to nitrogen deficiency, but starts on new growth instead of old.
• Iron: interveinal chlorosis on new growth specifically, the opposite pattern from magnesium.
• Zinc: stunted growth, distorted new leaves.
• Manganese: yellow or white spotting on leaves.
• Copper: wilting and browning leaf tips.

Fix for all of the above: confirm pH first, since most micronutrient lockouts are pH problems in disguise, then add a Cal-Mag or micronutrient supplement if pH is already correct.

pH Lockout: When It’s Not a Deficiency At All

Cannabis absorbs nutrients best in a slightly acidic to neutral range, roughly pH 6.0-7.0. Outside that window, specific nutrients become chemically unavailable even though they’re present in the soil, a false deficiency that no amount of extra feeding fixes. Low pH restricts availability broadly; high pH is the more common lockout trigger and specifically blocks iron, manganese, and other micronutrients.

Fix it: test pH before changing anything else. If it’s off, correct gradually with a pH up or down product rather than a single large adjustment, and recheck after the growing medium has had time to respond, not immediately.

When You’re Not Sure

Deficiency symptoms can look a lot like pest damage or disease, especially early on. If leaves are damaged, speckled, or spotted rather than uniformly discolored, check our common cannabis growing problems guide before assuming it’s a feeding issue.

Get Ahead of It

Paradise Seeds has been growing cannabis in Amsterdam since 1994, and nutrient problems are some of the most preventable issues a grower faces: a weekly pH check catches most of what’s on this page before it ever becomes visible. For the full picture on building a feeding schedule from the ground up, see our cannabis nutrients guide, or browse our feminized cannabis seeds collection to start your next grow with genetics bred to reward getting the basics right.