In today’s post, we’re going to do a simple, classic experiment to show exactly how plants eat and drink.  This is a great visual for a concept that can be a little hard to grasp and it couldn’t be easier! If you can fill a glass with water and drop in some food coloring, you have this experiment nailed! I’ve done a video with all the steps and an explanation of what’s happening, you can view it here if you and your kids want to watch.

As adults, it’s easy for us to assume that kids understand the basics of how plants grow and function.  It’s pretty easy stuff right?  But, if you think about it, the way plants drink and eat is pretty much the opposite of the way we do!  We take food and water in at the top of our bodies and it works its way down; plants intake food and nutrients below ground and move them upward.  If someone told you they eat through their feet, you’d have trouble with that concept too! 

Today we’re going to learn how trees drink by changing the color of some leaves.  Let’s get started!

Supplies:

  • Celery
    • I like to use the stalks from the center of the bunch because they have lots of nice leaves at the top to show off our color.
  • Mason Jars or Glasses
    •  I like to use clear containers because then we can see what’s happening to the stalk and leaves as time passes.
  • Food Coloring
    • Get something pretty dark so it will show well; I used red.
  • Water
    • Tap water is fine!

Step 1: Make The Water

  • Take a glass of water filled about ½ full..  
  • Drop food coloring in until it’s a nice dark color. 
    • I used red food coloring because the color shows through well.  
    • I put about 30 drops of coloring in mine, but yours will be different depending on the color you use, the amount of water you have, and the kind of coloring you use.  Just keep dropping until the water is really vivid.

Step 2: Add the “Trees”

  • Cut the base off the celery bunch
  • Pick out a stalk that has plenty of leaves at the top.  
    • Usually the best stalks for this will be in the center
  • Put the stem in the water.  
    • Try to avoid getting too much of the leaf in the water if you can. Leafy water can get gunky.

Observe

  • Each day, check out the leaves.  
    • It can take a day or so for any visible change to show up, so don’t worry if you don’t see anything at first.
    • By about day 2, you should see a pronounced difference in the leaves of your celery.  The leaves should be tinting around the edges.  
    • You may be able to see some subtle streaks of color up the stalk itself.  
    • By day 3, the color should be obvious throughout the leaf.  

If you want to see what my celery looked like, you can watch it here.

So what’s happening?  Why is the color changing?

The water comes up from the glass, or the ground in the case of plants and trees and the trees take it up through their roots.  

It’s a long way from the roots of a tree all the way up to the leaves at the tippy top.  How does the water get all the way up there?  The answer is that trees have a system of special veins and vessels just like your body does. In trees, these are known as xylem and phloem.

Xylem are the cells and vessels that move water in a plant. Phloem are the cells and vessels that move nutrients and sugars. Basically, the food.

When we watch the celery stalks change color over time, we’re watching the process as the xylem move colored water from the glass up through the stalk. The colored water moves up the veins as the water that was already in the leaves moves out of those leaves through something called transpiration.

Transpiration means water going out of the leaves and into the air.  We won’t see the water moving into the air because it comes off in tiny particles, but happens constantly, meaning water is constantly leaving the plant.

When water comes off the plant leaf, it leaves a little blank spot with no water.  The xylem moves water into the empty spot, and then it moves water into that resulting empty spot, and so on and so on all the way down the tree.  It’s like the water is moving forward in the line for a roller coaster, but the roller coaster is transpiration.

What we’re seeing as the leaves get more and more red is that more and more red water is moving up in line toward the edges and surface of the leaf and changing the leaf’s color.

Hopefully observing these leaves as they changed color from bottom to top helped provide a visual for your kids as they learn more about plants and how they grow! 

You can also do the same experiment with romaine lettuce leaves, which gives a cool visual of the leaves veins. Maybe do a compare/contrast with the lettuce and the celery. Or, a comparison of different colors of water, studying which color gives the best demonstration.  There are so many cool expansions you could do with this super simple experiment.  Take it and run!  Happy learning!