My family is installing a number of metal raised garden beds. Our native soil is about an in deep, thanks to it being removed during the house construction. Subsoil is heavy clay loam. I desired to fill the beds with soil mix. We ordered a truckload of compost and coco coir blocks. We wanted an aerating agent like vermiculite or perlite, without environmental or practicality concerns. Ground pumice could have filled the bill, but our midwestern north american location ensured transport costs for pumice were too high, as was the built-in carbon cost of this mined producf. Research suggested rice hulls. We are mixing 1/3 rice hulls into our planting mix and are delighted! It keeps the soilless mix light, helps moderate moistness, and works GREAT!!! It even has a pleasant scent- somewhat similar to a warm southern farm on a spring day. We are planning to mix some rice hulls into our mulch to help extent our mulch. Get this, it is wonderful!