Cannabis Nutrient Deficiency Chart: Visual ID Guide

Nitrogen (N) Deficiency

Nitrogen is essential for vegetative growth—it's a core component of chlorophyll and amino acids. Cannabis has a high nitrogen demand during the vegetative stage.

Symptoms

• Starts on lower/older leaves (plant moves N to new growth)
• Leaves turn uniformly pale yellow (no green veins)
• Yellow spreads from tips inward
• Affected leaves eventually die and drop
• Slow growth, pale green overall plant

Treatment

1. Verify pH is correct (6.0-7.0 soil)
2. Feed with nitrogen-rich fertilizer (look for higher first number in N-P-K)
3. Organic option: blood meal, fish emulsion
4. Improvement visible within 5-7 days

Phosphorus (P) Deficiency

Phosphorus is critical for flowering and root development. Deficiency is most common during bloom when P demands are highest.

Symptoms

• Starts on lower/older leaves
• Leaves turn dark green, then develop purple/blue hues
• Brown/bronze spots appear
• Stems may turn purple (though some strains do this naturally)
• Slow bud development during flower

Treatment

1. Check pH—P is locked out below pH 6.0
2. Switch to bloom-stage nutrients (higher P content)
3. Organic option: bone meal, bat guano
4. Ensure temperatures aren't too cold (below 60°F reduces P uptake)

Potassium (K) Deficiency

Potassium regulates water uptake, enzyme activation, and disease resistance. Deficiency often appears during heavy feeding periods or in coco coir grows.

Symptoms

• Leaf edges turn yellow/brown and curl upward
• Brown spots between veins
• Tips and edges appear burnt (similar to nutrient burn)
• Weak stems, slow growth
• Lower/older leaves affected first

Treatment

1. Verify pH (K locked out above 7.0)
2. Add potassium supplement or increase bloom nutrients
3. Organic option: kelp meal, wood ash
4. Coco growers: use coco-specific nutrients with extra K

Calcium (Ca) Deficiency

Calcium is essential for cell wall structure and root development. Very common in coco coir, RO water, and LED grows (coco binds Ca; RO water lacks it; LEDs increase Ca demand).

Symptoms

• Appears on NEW growth (Ca is immobile)
• Brown/rust spots on younger leaves
• Distorted, curled, or crinkled leaf tips
• Weak stems that break easily
• Stunted root development

Treatment

1. Add CalMag supplement (2-5ml per gallon)
2. Ensure pH is 6.2-6.5 for best Ca uptake
3. If using RO water, CalMag is REQUIRED
4. Organic option: dolomite lime (slow release)

Magnesium (Mg) Deficiency

Magnesium is the central atom in chlorophyll. Without it, plants can't photosynthesize efficiently. Often confused with iron deficiency.

Symptoms

• Appears on OLDER/lower leaves (Mg is mobile)
• Yellow between veins while veins stay green (interveinal chlorosis)
• Edges may turn brown/crispy over time
• Leaves may curl upward

Treatment

1. Add CalMag or Epsom salt (1 tsp per gallon)
2. Foliar spray for fast absorption
3. Check pH—Mg locked out below 6.0

Iron (Fe) Deficiency

Iron is needed for chlorophyll synthesis and enzyme function. Often caused by high pH rather than actual deficiency.

Symptoms

• Appears on NEW/top growth (Fe is immobile)
• Yellow between veins, veins stay green (like Mg, but on NEW leaves)
• Entire leaf may turn pale yellow/white in severe cases
• New growth is stunted and weak

Treatment

1. Lower pH to 6.0-6.5 (most common cause)
2. Add chelated iron supplement
3. Avoid overwatering (reduces root function)

pH Lockout Explained

pH lockout is the #1 cause of apparent nutrient deficiencies. Even if nutrients are present, plants can't absorb them if pH is wrong.

How to fix lockout:

1. Flush with 3x pot volume of pH'd water (6.5 for soil)
2. Let plant dry out slightly
3. Resume feeding at half strength with correct pH
4. Monitor runoff pH—should match input pH after flush

Nutrient Burn (Toxicity)

Too much of a good thing is bad. Nutrient burn happens when you feed too heavily.

Symptoms

• Brown, crispy tips on all leaves (not just old ones)
• Dark green leaves that look "waxy"
• Leaves curl downward ("the claw") with nitrogen toxicity
• Burned tips spread inward as it worsens

Treatment

1. Flush with plain pH'd water immediately
2. Skip feeding for 1-2 waterings
3. Resume at 50% strength
4. Monitor runoff EC/PPM