Soilless media, sometimes called growth media or substrates, are one of the most important components of crop production in containers or raised beds with restricted volume. The word media is the plural of medium. The physical and chemical properties of media greatly influence optimal management protocols. Primary components of these media may be peat, pine bark, perlite, vermiculite, compost and/or perhaps coarse sand. Understanding the chemical and physical properties of optimal media, or the chosen medium for a production system, allows more effective system management. Although choosing or formulating media with optimum physical properties (such as pore air space and water holding capacity) for a given production environment and crop plant is important, this publication focuses on the chemical properties of soilless media determined with a laboratory test as conducted through the University of Kentucky Cooperative Extension Service at the Division of Regulatory Services Soil Testing Laboratories.
Ingram, Dewayne L., "Understanding Soilless Media Test Results and Their Implications on Nursery and Greenhouse Crop Management" (2014). Agriculture and Natural Resources Publications. Paper 161.