Roots require oxygen and water for optimal growth. In soil, water and air are held in pore spaces between soil particles. Larger pores (macropores) are important to promote good aeration, they hold oxygen. Smaller pores (micropores) are important for absorbing and holding water.⠀ ⠀ In order to have a good soil structure, with macro and micro pores, you need a good ratio of small, medium, and large particles in the potting mix. Soil that contains only small particles will only have micro pores. I