Orku 20L Coarse Perlite Soil Additive for Drainage and Aeration - Growing MediumOrku 20L Coarse Perlite Soil Additive for Drainage and Aeration Growing Medium Perlite is a light, hard, aerated, white mineral, formed from volcanic glass, used in potting mixes to add open and porous drainage, provide aeration to plant roots and hold oxygen, a little moisture and nutrients from soluble fertilisers. Perfect for creating your own potting mix or raised bed mix in bulk. Simply add compost, soil and other components to make your own