What is "growing medium"?

Growing medium is the material in which the roots of the plant are growing. This covers a vast variety of substances which include Rockwool, perlite, vermiculite, coconut fiber, gravel, sand and many more. The growing medium is an inert substance that doesn't supply any nutrition to the plants. All the nutrition comes from the nutrient solution (water and fertilizer combined). You can therefore, easily control everything the plants receive. The strength and pH of the nutrient solution is easy to adjust so that the plants receive just the right amount of food. The watering/feeding cycles can be controlled by an inexpensive timer so that the plants get watered on schedule, as needed.