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Aeration in potting mix explained


January 22, 2024


The Searles Gardening Team

For potting mixes to allow the water and air to move freely through the blend they need porosity. Porosity necessitates a texture that creates pockets or gaps. This is one of the most important features of a potting mix, as this is where the water flows through, the roots extend into the space and the air allowed to circulate. Without this, the mix would be hard and compact and restrict growth and water access.

How is soil porosity achieved? Unlike Tetris, the old game we once played that allowed you to build a wall and leave no gaps to win with similar size pieces, using similar size fragments in a potting mix would block air and water flow andprevent root penetration.  On close examination quality potting mix consists of small, medium and large components and the largest of these is to allow for excellent water flow.  They are deliberately blended into the mix to create pathways; it is scientifically balanced for maximum plant growth.  


Potting mix will keep breaking down after you first plant into it and if it were all the same size you would not have the longevity in the mix. Have you noticed that the potting mix seems to settle after a period of time and the soil level drop? If it were all the same size elements, it would compact and shrink significantly over a shorter period. When you see larger pieces in the mix, this provides better aeration of the soil mix for a longer, resulting in healthier and better plant growth.