Growing Media
Growing media is the material plants root into, such as soil, sand, water, or cotton.
A potting tray holds a layer of soil where seeds sit and push roots down. The soil grips the roots and holds water near them. You could swap the soil for sand or gravel, and roots would still spread through it. That fill is the growing medium: the base that roots anchor into.
Explaining growing media by grade level
Plants need something to hold their roots. You can grow a pinto bean in cotton or in soil. The cotton holds water near the roots. Each material gives the plant a different start.
Projects that explore growing media
Not all growing media are equal when it comes to rooting speed. Sixteen pineapple crowns are split into four groups — potting soil, sand, plain water, and soil with added fertilizer — and root growth is measured each week. The results challenge the obvious assumption: the crowns in plain water root faster than any other group. Soil and fertilizer do not speed things up. A simpler medium, it turns out, can outperform richer ones.
Different growing media deliver nutrients to roots in different ways. Soil releases minerals slowly as water passes through it. A flood-and-drain system soaks the roots three times a day in nutrient solution. A water culture system uses an air pump bubbling nutrients around the roots nonstop. In one experiment, soil-grown radishes averaged 5.75 cm tall. The flood-and-drain group reached 3 cm, and the water culture group reached only 2.5 cm. The medium roots sit in shapes how well the plant takes up what it needs.
The material roots grow into affects the whole plant. One experiment tested five plant types in two setups. One used cups filled with potting soil. The other used cups filled with sand and water. After 35 days, all five types grew better in soil. The growing medium determined which group produced taller and heavier plants.