Soil and Substrate Types

Mineral soils

Sandy soils

• Low bulk density
• Low WHC
• High drainage
• Low nutrient buffering
• Rapid nutrient leaching

Loamy soils

• Balanced particle size
• Moderate WHC
• Good structure
• High biological activity
• Agronomically versatile

Clay soils

• Low bulk density
• High WHC
• Slow drainage
• High CEC
• Sensitive to compaction and sodium

Organic and manufactured substrates

Coir

• Low bulk density
• High WHC
• Rapid drainage when structured
• Low buffering unless charged

White peat

• Very high WHC
• Low bulk density
• Acidic
• Good nutrient retention when managed

Bark-based substrates

• High air-filled porosity
• Lower WHC
• Strong biological activity
• Nitrogen immobilisation risk

Wood fibre / wood chip

• Extremely low bulk density
• Rapid drainage
• Very low buffering
• Strong C:N effects

Green waste composts

• Variable bulk density
• Often high salts
• Strong buffering
• Nutrient release unpredictable

Key concept

Soils and substrates differ more in physical behaviour than chemical composition — and plants respond to physics first.