Easy Leaf Transpiration Experiment

Demonstrate how plants “sweat” like humans through this leaf transpiration experiment. Your kids will be surprised by how much water the plant releases through transpiration!

Leaf Transpiration Experiment

When teaching your elementary students about the water cycle, you usually talk about evaporation from bodies of water, condensation of water vapors into clouds, and then precipitation, or rain. But do you know that plants also contribute to the formation of clouds?

Transpiration is a process by which water is lost from plants into the atmosphere in the form of water vapor. It is part of the water cycle, which describes how water evaporates from oceans, rivers, and other water sources, rises into the atmosphere and forms clouds, and falls back to Earth as precipitation, continuing the cycle once again.

With just some clear, sealable plastic bags, you can explore how plant cells regulate their internal water balance. Your kids will be surprised to see the water inside the plant escape into its surroundings – all thanks to transpiration. This is always a great way to obtain drinkable water if you are stuck in the wilderness. Survival skills for the win!

So let’s get this transpiration experiment underway!

Plant Transpiration Experiment

Before conducting this plant experiment, check the weather forecast and make sure it’s going to be a sunny day. The heat from the sun will allow the transpiration process to happen quickly instead of waiting for hours.


  • Ziploc bags
  • Plants with leaves


1. Pick out at least two species of plants in your house or backyard. Make sure that the plants are well-hydrated; you may want to water your plants prior to this transpiration experiment.

Try and select plants with different kinds of leaves. For example, it would be interesting to pick a deciduous tree with broad leaves and a coniferous tree with needle-like leaves for your experiment. We do not have any coniferous trees around, so we chose two different species of deciduous trees.

2. Grab a few twigs with leaves and place the Ziploc bag over the leaves.

3. Close the Ziploc bag as much as possible around the twigs. If the twigs or branches are too thick, you may want to use a rubberband or a twist tie to seal in the leaves.

Make sure one corner of the Ziploc bag is lower than the rest. The water will collect on the bag and drip down to the corner.

Transpiration Experiment Bag Over Leaves

The size of the Ziploc bag will depend on the plant you choose. We used a gallon bag on our big privacy trees in the backyard, and a sandwich bag for the small bush in our front yard.

Small Transpiration Experiment Bag Over Leaves

4. Come back in a few hours to check on your leaves. The time will vary depending on how hot and sunny it is outside where your plants are. If you live in a sunny desert like me, it would only take a couple of hours to get a decent amount of water in the plastic bag!

Transpiration Experiment Condensation in Large Bag

There was not as much condensation in the small bag, but that’s because I was only able to fit 1 twig with leaves in the bag.

Transpiration Experiment Condensation in Small Bag

5. (Optional) You can continue to transpiration experiment by leaving the bag on the plants for an additional few hours to see if the leaves will “sweat” out more water.

We did leave the bags for a couple more hours after the first observation. There was definitely more liquid in the bags by the time we took them off.

Here is how much water we collected in the large Ziploc bag:

Transpiration Experiment Water in Large Bag

And here is how much water we collected in the small Ziploc bag:

Transpiration Experiment Water in Small Bag

Science Behind the Leaf Transpiration Experiment

Transpiration is a process that plants use to get rid of extra water that they don’t need. Just like people sweat when they’re hot, plants “sweat” too – but instead of sweat, they release water vapor through tiny holes on the underside of their leaves, called stomata. This process is called transpiration.

Transpiration is essential for plants to grow and stay healthy. When plants take in water from the soil through their roots, not all of it is needed for photosynthesis (the process by which plants make their own food). Transpiration helps the plant to get rid of the extra water that it doesn’t need.

In addition to getting rid of extra water, transpiration also helps plants to keep cool. When water is released from the plant during transpiration, it creates a cooling effect that helps to regulate the plant’s temperature. So, just like how people sweat to cool off, plants use transpiration to keep cool.


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