Why CalMag Deficiencies Are So Common

Calcium and magnesium deficiencies have become epidemic in modern cultivation. Understanding why helps you prevent problems before they occur.

Coco Coir: The Cal-Mag Thief

Coco coir's popularity stems from its excellent water retention, drainage, and sustainability. However, coco naturally binds calcium and magnesium through a process called cation exchange.

Coco fibers carry negative electrical charges that attract and hold positively charged nutrients (cations)—especially calcium (Ca²⁺) and magnesium (Mg²⁺). Even when your nutrient solution contains adequate Cal-Mag, coco coir strips these elements before plant roots access them.

Result: Plants in coco almost always need CalMag supplementation, regardless of base nutrient quality.

RO Water: Starting From Zero

Reverse osmosis filtration removes dissolved minerals, including the calcium and magnesium naturally present in most tap water. Growers use RO water for precise nutrient control—but this creates a blank slate lacking the baseline Cal-Mag that tap water provides.

Many nutrient formulas assume some calcium and magnesium from water sources. When that assumption fails (RO, distilled, or very soft water), deficiencies emerge despite apparently adequate feeding.

LED Lighting: Increased Demand

LED technology has transformed cultivation with energy efficiency and spectral control. However, plants under LED lighting consistently show elevated calcium and magnesium requirements compared to traditional HID lighting.

The mechanisms aren't fully understood, but practical experience across thousands of grows confirms: LED grows need more Cal-Mag. The combination of efficient photosynthesis and different heat profiles appears to increase metabolic demand for these elements.

Modern Genetics

Selective breeding for yield, potency, and speed has created plant varieties with higher overall nutrient demands. Many modern genetics are particularly calcium-hungry, requiring supplementation that their ancestors never needed.

The Science: Calcium in Plants

Structural Role

Calcium is a primary component of cell walls. It cross-links pectin molecules in the middle lamella (the "glue" between cells), providing:

• Mechanical strength to resist physical damage
• Barrier function against pathogen penetration
• Cellular integrity during rapid growth

Plants deficient in calcium develop weak, easily damaged tissue prone to disease and structural failure.

Signaling Role

Calcium acts as a "second messenger" in cellular signaling—when plants detect environmental changes (light shifts, temperature, stress, pathogens), calcium signals trigger appropriate responses. This regulatory role affects:

• Stomatal opening and closing
• Root growth direction
• Defense responses to stress and pathogens
• Hormone signal transduction

Critical Characteristic: Immobility

Once calcium is incorporated into cell walls, it cannot be redistributed. This immobility means:

• Deficiency symptoms appear in newest growth first
• Plants cannot "borrow" calcium from old leaves to support new growth
• Continuous supply is essential—calcium must be available in the root zone when new cells form

The Science: Magnesium in Plants

The Chlorophyll Connection

Magnesium sits at the center of every chlorophyll molecule. Without adequate magnesium, plants cannot produce the chlorophyll needed for photosynthesis—regardless of how much nitrogen (also required for chlorophyll) is available.

This is why magnesium deficiency causes yellowing (chlorosis): reduced chlorophyll means reduced green pigmentation.

Enzyme Activation

Magnesium activates numerous enzyme systems involved in:

• ATP synthesis and energy transfer
• Protein synthesis
• Carbohydrate metabolism
• Nucleic acid synthesis

Critical Characteristic: Mobility

Unlike calcium, magnesium is mobile within plants. When deficient, plants pull magnesium from older tissue to support new growth. This means:

• Deficiency symptoms appear in older/lower leaves first
• Plants sacrifice old leaves to protect new growth
• Severe deficiency progresses upward through the plant

Identifying Deficiency Symptoms

Calcium Deficiency Symptoms

Magnesium Deficiency Symptoms

What's Inside CalMag

Why Chelated Iron?

Iron often accompanies Cal-Mag deficiency because all three elements become less available at high pH. The EDTA-chelated iron in CalMag remains available across pH 4.0-6.5, ensuring plants maintain green coloration even when conditions would otherwise limit iron uptake.

When Do You Need CalMag?

CalMag is ESSENTIAL if you're:

• ✅ Growing in coco coir (always use CalMag)
• ✅ Using RO, distilled, or very soft water (<100 PPM)
• ✅ Growing under LED lighting
• ✅ Growing autoflowers (high growth rate increases demand)
• ✅ Seeing deficiency symptoms described above

CalMag is RECOMMENDED if you're:

• Using moderately soft water (100-200 PPM)
• Growing heavy-feeding varieties
• Pushing plants hard with high light intensity
• Using inert media (perlite, rockwool, clay pebbles)

CalMag may be OPTIONAL if you're:

• Growing in quality soil with tap water containing 200+ PPM minerals
• Using traditional HID lighting (HPS, MH)
• Growing moderate-demand varieties at moderate intensity

When in doubt, use CalMag. Mild oversupply causes no problems; deficiency causes permanent damage.

Application Guide & Dosage

Standard Dosage

Frequency

• Coco coir: Every watering, without exception
• Hydroponics: Include in every reservoir
• Soil with RO water: Every watering
• Soil with tap water: Every other watering or as needed

Target Ranges

• pH: 5.8-6.5 (CalMag availability decreases above 6.5)
• Total solution EC: CalMag adds approximately 0.2-0.3 EC at 2 mL/gal

Mixing Guide

Correct Mixing Order

1. Water: Start with your base water
2. Silica (if using): Armadillo Armour first—let dissolve fully
3. CalMag: Add and stir thoroughly (30+ seconds)
4. Micro: Base nutrient foundation
5. Grow/Bloom: Base nutrients
6. Other additives: Bud Booster, Sticky Bandit, etc.
7. pH adjustment: Always last

Plants & Growing Systems

Works With All Plant Types

• Cannabis: Both photoperiod and autoflowering varieties
• Tomatoes: Prevents blossom end rot (calcium deficiency symptom)
• Peppers: High calcium demand during fruiting
• Leafy greens: Lettuce, spinach, herbs
• Flowering ornamentals: Roses, orchids, etc.
• Fruiting vegetables: Cucumbers, squash, melons

Growing System Compatibility

Compatibility

Works With

• Classic 3-Part: Micro, Grow, Bloom—use at every feeding
• Bonnie & Clyde: Essential for autoflower success
• All Cronk additives: Bud Booster, Sticky Bandit, Armadillo Armour, Monkey Juice

NOT Compatible With

• PuurOrganics line: Use PuurCalMag instead for organic grows
• Concentrated hydrogen peroxide: Can degrade chelated iron

Note on PuurCalMag

For OMRI-certified organic growing, use PuurCalMag instead. Standard CalMag contains synthetic chelates that don't meet organic standards. PuurCalMag uses organic acetic acid chelation.

Troubleshooting

Deficiency Symptoms Persist Despite CalMag Use

Possible causes:

• pH too high (above 6.5 locks out calcium and magnesium)
• Dose too low for your conditions
• Not using at every feeding in coco

Solution: Check pH first—this is the #1 cause. Increase dose if pH is correct. Ensure consistent application in coco.

Nutrient Burn After Adding CalMag

Cause: Total nutrient concentration too high; CalMag adds to overall EC.

Solution: Reduce base nutrient doses slightly when adding CalMag. Total EC should stay within target range.

White Residue or Precipitate

Cause: Calcium reacting with other nutrients (usually phosphates).

Solution: Check mixing order—CalMag should go in before phosphorus-containing nutrients. If precipitate forms, discard and remix properly.

Frequently Asked Questions

Related Resources

• Diagnosing Nutrient Deficiencies
• Growing in Coco Coir
• RO Water and Nutrient Management
• LED Growing Tips
• Classic 3-Part Feeding Schedule