Nutrient IssuesModerate
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
1Foliar spray with Epsom salt for immediate fix
2Add Cal-Mag for long-term prevention
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
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.
Not sure what you're looking at?
Upload a photo of your plant and our AI will diagnose the problem in seconds — free.
Open AI Plant Diagnosis →Related problems
Get Your Free Grow Checklist
Download our free printable checklist covering everything from seed to harvest. Perfect for first-time growers!
No spam, ever. Unsubscribe anytime.