Common Substrates: Chemistry and Behaviour

Coco coir

• Moderate CEC, often K-dominant
• Responds quickly to fertigation chemistry
• High K can suppress Ca and Mg uptake
• Requires deliberate Ca and Mg supplementation

White peat

• Very high CEC and good nutrient retention
• Buffered initially but can drift upward under hard water
• Micronutrient lockout (Fe/Mn/Zn) common if pH rises

Bark (fresh vs composted)

• Variable CEC, structural and free-draining
• Fresh bark has high C:N and can immobilise nitrogen
• Composted bark is more stable but still may need higher early N

Wood chip / wood fibre

• Very high C:N, strong nitrogen immobilisation risk
• Low nutrient contribution and low buffering
• Not suitable as a primary medium unless thoroughly composted and managed

Green waste compost

• Variable chemistry and maturity
• Can contribute nutrients but may be inconsistent
• Often higher EC and pH; can carry Na/Cl depending on source
• Immature compost can immobilise nitrogen and cause instability