What plants stand in: growing media

Students will

• Explain what a growing medium does for a plant in hydroponics.
• Sort common growing media into ones that hold water and ones that drain fast.
• Explain why roots need a balance of water and air.

New words

growing medium

What a plant stands in instead of soil, like rockwool or clay pebbles.

Talk about it

Which shoes would you pick for a rainy day, and which for the beach? Why?

Check questions and answers

1. What does a growing medium do?

   • Holds the plant up and gives roots a grip (answer) Right. It works like shoes for the roots.
   • Feeds the plant Not quite. The food is in the water. The medium holds the plant.
   • Makes light for the leaves Not quite. Light comes from the sun or a lamp.

2. Which medium drains the fastest?

   • Clay pebbles (answer) Right. Water runs off them, and air fills the gaps.
   • Rockwool Not quite. Rockwool soaks up water like a sponge.
   • Coco coir Not quite. Coco coir holds lots of water.

3. The roots stay soggy all the time. What could help?

   • A medium that drains faster (answer) Right. When water drains away, air can reach the roots.
   • A medium that holds more water Not quite. These roots already have too much water.
   • Pack the medium down tight Not quite. Packing it down squeezes out the air.