Particle size describes whether a grow mix is built with mostly small, medium, or large particles, and how that size balance affects air movement, water retention, and dry-down behaviour in the root zone. It explains the physical structure of the mix, not how much water is added or how often watering occurs.
Particle size matters because it determines the shape and connectivity of pore spaces. Larger particles create bigger air channels that drain quickly and re-oxygenate fast. Smaller particles pack tightly, holding more water but restricting airflow and slowing oxygen return to roots.
Common particle size bias categories used in plant profiles include:
Fine — Dominated by small particles. Holds water for longer but restricts airflow and narrows the margin for error for oxygen-sensitive plants.
Balanced — A mix of particle sizes that supports both moisture retention and reliable oxygen movement. Dry-down is steady and predictable.
Medium–Coarse — Leans toward larger particles. Drains and re-oxygenates quickly, with faster dry-down and reduced risk of oxygen restriction.
Coarse — Primarily large particles. Maximizes airflow and oxygen availability but retains less water, increasing sensitivity to drying if light and water use are high.
In short, particle size explains how the physical makeup of a mix controls air and water behaviour, helping plant parents understand why two mixes with the same ingredients can behave very differently indoors.
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