How do I fix potassium deficiency on cannabis?

Older leaves develop brown, scorched edges (leaf scorch) and may curl. Plants become weak and more susceptible to disease. Potassium is vital for water regulation and fruit quality. Supplement with a high-potassium booster during late veg and early flower. Verify pH is 5.8–6.3 (official chart). Reduce excess Ca/Mg if levels are above target.

Visual Guide

Potassium Deficiency.

Supplement with a high-potassium booster during late veg and early flower

← All problems

Brown, scorched edges on older leaves (leaf scorch)

Photo

Deficiencies

Older leaves develop brown, scorched edges (leaf scorch) and may curl. Plants become weak and more susceptible to disease. Potassium is vital for water regulation and fruit quality.

Looks like this

Brown, scorched edges on older leaves (leaf scorch)
Curling or rolling of leaf margins
Weak stems and reduced flower or fruit quality

Solve it with Vitaponix

VitaBulk →

Replaces VitaBase from week 7 at 5 ml/L; steers the plant towards heavier flowering.

VitaSilica →

High-quality silica with added potassium, 1 ml/L from week 2. Supports sturdier plants.

How to fix it

Supplement with a high-potassium booster during late veg and early flower
Verify pH is 5.8–6.3 (official chart)
Reduce excess Ca/Mg if levels are above target

Why it happens

Insufficient potassium in late-veg/early-flower feed
High calcium or magnesium levels causing antagonism
Cold root zone reducing potassium uptake

Prevent it

Use a P-K booster during the transition to flowering
Maintain a balanced base feed and stable pH
Keep the nutrient solution at 18–21 °C (official chart)

Official feeding chart

Target pH (official chart): 5.8 – 6.3
VitaBulk: 5 ml/L from week 7

Doses and targets come from the official Vitaponix feeding chart. Vitaponix nutrients are plant nutrition, not pesticides or fungicides.

Prevent it next time

Get the full 10-week feeding schedule.

Open the feeding chart Shop Vitaponix →