The growing medium is used to anchor the plant, provide drainage, and allow oxygen to reach the plant roots. There are many types of growing mediums: soil, rockwool, pea stone, coco fiber are only a few examples. A good growing medium has a few basic characteristics. First, it must be sterile to help hinder the spread of disease. The medium must also be dense enough to hold the plant without interfering with the flow of nutrients and oxygen. The bits of the medium should be able to maintain dampness between feedings, and should have a neutral pH. And, finally, the growing medium should be suitable to the containers and easy to work with.