What Is a Soilless Growing Medium? A soilless growing medium is any material used for planting that does not contain field soil or dirt . It’s what you’ll use to fill your raised bed or grow box. Understanding how growing media work helps you choose the best option for healthy, productive plants. Why Growing Media Matters. A good growing medium performs two essential functions: Anchorage: It supports the plant by holding the roots firmly in place. Root Health: It supplies roots with water, nutrients, and air , all of which are critical for growth. What Makes a Good Growing Medium for Raised Beds or Grow Boxes? The material you choose should: Allow roots to grow freely between particles. Provide pore spaces for air and water movement. Hold enough moisture and nutrients to keep plants healthy. Drain excess water easily to prevent waterlogging. Be free from weeds, pests, and diseases. Recommended Soilless Materials (Choose one of the following as your base material) Pro-Mix o...