This goes hand in hand with our Sterilized grain spawn. We have this soil mixture specially crafted in house by our team of soil scientists. This substrate is perfectly hydrated and then air locked and sterilized 3 times over. This can guarantee you 100% sterilization every time. These Bags come in 4 pound unit sizes which are perfect ratio to use 3 bags per large mono tub. A special blend that is packed with nutrients that your mycelium actually need to thrive and grow.