Capillary Action Experiment: Today's STEM Play of the Day

Jun 19, 2020

Have you ever wondered how plants drink water through their roots? In today’s STEM Play of the Day from the Ripken Playbook, you will learn how capillary action helps plants grow through a fun, at-home experiment! 

What is Capillary Action?

Capillary action is how plants drink from their roots! When water seeps into soil, it travels through a plant's roots to the plant's cells to help it stay hydrated and healthy.

In this experiment, you will imitate the way a plant uses capillary action to drink using a few at-home materials.

Check out this video to watch a demonstration of today’s Capillary Action Experiment!


  • 2 cups of equal size
  • A paper towel sheet 
  • Food coloring (optional, but makes it more visually effective. Liquid food coloring recommended)
  • Water

Capillary Action Experiment

  • Fill one cup over halfway with water
  • Add food coloring until color is consistent
  • Fold the paper towel sheet until it is a long strip, 1-2 inches wide
  • Place the second, empty cup approximately two inches from the filled cup
  • Fold the paper towel into a “U” shape. Place one end in the empty cup, and one end in the full cup.
  • Leave the glasses for approximately an hour, and then come back check on your experiment! 


  • What happened in your experiment?
  • How much water is left in the original, full cup? 
  • How much water is now in the original, empty cup? 
  • Can you think an instance you have seen capillary action in nature or elsewhere? 

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