Leaf Transpiration Experiment – Simple Spring Science for Kids
This post may contain affiliate links.
Did you know that plants transpire? It’s kind of like perspiring—but with a fascinating twist. This easy and eye-opening leaf transpiration experiment is a perfect outdoor science activity for spring or summer. It’s low-prep, kid-friendly, and teaches one of the most important processes in the plant world.
We first tried this experiment as part of my son’s preschool curriculum, and I was amazed at how cool it was. Years later, it still makes a great addition to any nature study or backyard science lesson.
What Is Transpiration? (The Science Behind It)
Transpiration is the process of water moving through a plant and evaporating from its leaves, stems, and flowers. While plants absorb water through their roots, they only use a small amount—about 1%—for growth and photosynthesis. The remaining 99% is released back into the atmosphere through transpiration.
On the underside of most leaves are tiny pores called stomata. These pores open to allow carbon dioxide (CO₂) in for photosynthesis, but when they open, water vapor escapes as well. This process helps cool the plant, maintain nutrient flow, and contributes to the global water cycle.
When you trap a leaf inside a sealed plastic bag, you’re creating a mini-greenhouse that captures this water vapor as it escapes—making transpiration visible.
How to Do the Leaf Transpiration Experiment:
You’ll Need:
- 1 clear plastic bag (sandwich or quart-size)
- 1 rubber band or twist tie
- A leafy branch on a living tree or shrub
- Sunny weather
- (Optional: magnifying glass, journal, printable recording sheet)
Instructions:
- Choose Your Leaf – Find a healthy, leafy branch on a tree or shrub. The bigger and greener the leaf, the better!
- Cover the Leaf – Place a clear plastic bag over one leaf or small group of leaves. Gently gather the bag around the stem or branch and secure it tightly with a rubber band or twist tie. Make sure it’s sealed well so no air escapes.
- Observe – Watch the inside of the bag closely. Within a few minutes on a sunny day, you may begin to see fog or tiny droplets forming on the inside of the plastic.
- Wait and Check – Leave the bag for a few hours (or overnight). When you return, you’ll likely see visible water droplets—sometimes even small puddles—collected inside.
Being a busy absent-minded mom, I forgot about it until the next day. I reminded my son and we went running out to the yard to see what might have happened. We were both quite surprised to see quite a lot of water had collected in the plastic bag!
What Happened?
That water came from inside the leaf! The plant pulled water up through its roots and into the leaf, and as it opened its stomata to breathe in carbon dioxide, water vapor escaped into the bag. Without the bag, it would have entered the air invisibly—but now you can see it!
This is a great visual demonstration of how plants “sweat,” how water cycles through nature, and how important plants are in maintaining atmospheric moisture.
Real-Life Application: My son asked if he could drink the water from the bag—it was clear, but very smelly, so I said no! Still, this method is actually similar to how a solar still can be used to collect clean water in an emergency.
Optional Discussion Questions:
- Why do you think the leaf releases so much water?
- What do you think would happen if we tried this on a rainy or cloudy day?
- Would different plants release more or less water?
- Why is transpiration important for the Earth?
Variations on This Experiment
- Test different types of plants or trees and compare the results
- Try it on a hot day vs. a cooler day
- Use a magnifying glass to examine the bottom of a leaf and look for stomata
- Use a scale to weigh the bag before and after
- Record observations in a science notebook
Why This Leaf Transpiration Activity Is So Effective:
This project takes a concept that’s often invisible and makes it easy to observe in real life. It’s a perfect example of learning by doing—and even as an adult, it made the process of transpiration finally click for me.
If you’re building a nature study, unit on plants, or looking for a hands-on way to explore environmental science, this activity fits beautifully.
Looking for more nature science ideas?
Check out these:
what if the branch had no leaves??? :))
Well, I think you may need to wait until another season 😉
Does the shoot become red at the end of the expirement…if yes plz give me an explaination to why it turned red.
What happens to the leaf after two weeks