Growing medium is the product that you plant the roots of your plants in. Whatever container you choose to grow your plants in, the roots of the plant must sit in a soil medium. Containers much have holes for drainage so that the moisture can run off the growing medium and not remain soggy. Types of growing mediums include soil or soilless mixes of all sorts that might be suitable to grow plants. Common mediums may comprise organic potting soil, vermiculite, gravel, coco coir, or peat moss.