Calcium Deficiency in Cannabis
Calcium deficiency is extremely common in coco coir grows and when using RO or filtered water. It shows up as small rust-colored spots and distorted new growth.
What it looks like
- ●Small rust-colored or dark-brown spots on young leaves
- ●New growth may look twisted or distorted
- ●Hooking leaf tips or necrotic spots
- ●Common in the upper part of the plant (calcium is immobile)
Quick diagnostic checks
Measure before you treat
Plant diagnostic essentials
These tools help confirm the cause of calcium 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 calcium in water/feed
Most commonSigns
- ●Using RO, distilled, or filtered water
- ●Growing in coco coir
- ●Not using Cal-Mag supplement
Fix
- ✓Add Cal-Mag at 3-5 ml/gal every feeding
- ✓Coco + RO water ALWAYS needs Cal-Mag — mandatory
Recommended products
Botanicare Cal-Mag Plus
Essential for coco and RO setups
2. pH too low for calcium uptake
CommonSigns
- ●Runoff pH below 6.0 in soil
- ●Calcium is in feed but not absorbing
Fix
- ✓Raise water pH to 6.3-6.5 (soil) or 5.8-6.2 (coco)
- ✓Use pH Up to adjust
⚠️When to worry
Cal deficiency during flower can cause bud defects and lower yield. Fix promptly.
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