Magnesium Deficiency in Cannabis
Magnesium is mobile in the plant, so deficiency shows up on lower leaves first — the plant pulls Mg from old leaves to feed new growth.
What it looks like
- ●Yellow between veins (interveinal chlorosis) — veins stay green
- ●Starts on lower leaves and works upward
- ●Leaf tips may curl upward
- ●Advanced: rust-colored spots appear
Quick diagnostic checks
Measure before you treat
Plant diagnostic essentials
These tools help confirm the cause of magnesium deficiency before you change nutrients, watering, or the environment.
VIVOSUN pH and TDS Meter Combo
Check root-zone pH and nutrient strength before changing a feeding plan.
Check price on AmazonBotanicare Cal-Mag Plus
Useful when filtered water, coco, or a confirmed calcium-magnesium issue is involved.
Check price on AmazonFoxFarm Liquid Nutrient Trio
A complete, staged nutrient system for vegetative growth and flowering.
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Causes ranked by likelihood
1. Not enough Mg in feed (common with soft/RO water)
Most commonSigns
- ●Using RO or soft water
- ●Growing in coco
- ●Not using Cal-Mag
Fix
- ✓Add Cal-Mag (contains Mg)
- ✓Or foliar spray with 1 tsp Epsom salt per quart water
Recommended products
Botanicare Cal-Mag Plus
Fixes most Mg deficiencies — essential with RO water or coco
2. pH too low
CommonSigns
- ●Runoff pH below 6.0 in soil
Fix
- ✓Raise pH to 6.3-6.8
⚠️When to worry
Progressive Mg deficiency in flower hurts bud development. Catch early.
Gear that prevents this problem
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