Automatic Watering | DFRobot Science Lab Season 2 EP11

AshG Mar 18.2021

DFRobot Science Lab Season 2 


EP11: Automatic Watering





5-LS1-1 Demonstrate that plants get the nutrients they need for growth mainly from water and air.

Science - Grade 3-5


This lesson will begin with the question “Why towels can absorb water” to lead students to discuss and get to know the capillarity action of water. They will be asked to make an automatic watering device based on the capillarity action principle, and explore how to improve the watering efficiency by enhancing the capillarity or reducing water evaporation.


According to the NGSS standard engineering design requirement in 3-5 grades, the course is divided into 3 parts, they are respectively “DEFINE ENGINEERING PROBLEMS, DEVELOPING POSSIBLE SOLUTIONS, OPTIMIZING THE DESIGN SOLUTION”. Just like engineers, students will find problems, set goals, design plans, build and test models, optimize and improve models, and finally complete the engineering design task.




Play and Learn with Boson Science Design Kit:



Find Problems

We always grow flowers at home, but when we travel, there is a problem that the flowers will be unattended, and even wither because of lacking water.

Can we design an engineering device to realize the function of automatic watering?


Engineering Goals

Make an automatic watering device.


After determining the engineering goals, let us follow the process of “Brainstorming-Drawing Prototype Diagram-What You Need-What You Do-Test and Evaluate” to develop a solution and complete the structure of the automatic watering device.


Let’s first brainstorm how to build an automatic watering device. In the process, try to draw a prototype of the automatic watering device.


Draw Prototype Diagram

In the brainstorming, we have initially understood the function and structure of the automatic watering device. Try drawing a prototype diagram. In the production process, the prototype diagram will be an important reference.

What You Need


What You Do


Soil moisture change table:


Test and evaluate

Through the above steps, a simple automatic watering device is completed! When we touch the cotton rope with our hands, we will find that the cotton rope becomes wet, because it sucks up the water in the breaker, and the water will follow it to the soil, which realizes the automatic watering function.

Observe and compare the changes in soil moisture. Is the efficiency of the watering device of each group of students the same? Think about it, do you think there is still room for improving the device? How to improve the efficiency of watering? Try proposing an optimization plan to improve the watering efficiency.




What You Do

Based on the brainstorm, select an optimization plan.

Use BOSON soil moisture sensor to observe the changes of soil moisture and record them in the table below.

Optimized soil moisture change table:


Test and evaluate

Draw the table of activity 1 and activity 2 onto one line chart and observe whether the watering efficiency is improved.

What happened?

As we said before, the soil can hold water because there are many small pores, which form the capillarity. The capillarity allows water to overcome its gravity and adhere to the small pores.

Cotton rope can absorb water for the same reason. Observing the cross-section of the rope, it can be seen that it is very loose and porous. There are also many small pores in the cotton rope. When the cotton rope encounters water, the capillarity will cause the water to overcome its gravity and climb up the cotton rope to fill these small pores. We know that water always flows from a higher place to a lower one, but through the capillarity, "water goes to a high place" is realized.


Further Development

In this activity, we made a very simple automatic watering device, and we can also try adjusting many variables in the design to make it better. For example, we can also change the watering efficiency by changing the thickness or quantity of the rope, or use a straw to cover the rope to reduce the evaporation of water. Students who are interested can give it a try!

Besides, some plants like water, while some don’t, such as cacti. When using an automatic watering device in practice, it is recommended to  learn whether the plants like water first!

Science Background

What is capillarity?

We know that because the soil and cotton rope are both loose and porous, the capillarity produced in the small pores allows the water to overcome its gravity and adhere to the pores. Capillarity can be understood as the attraction of small pores to liquid. Capillarity allows liquid to flow in narrow pores even under the action of gravity. The smaller the pores, the stronger the capillary action. When the pores become larger, the capillarity will become weaker due to the influence of gravity.

In life, capillarity exists everywhere, such as absorbent towels, candle wicks, alcohol wicks, etc. In addition, plants cannot absorb water without capillarity. In plants, there are many tiny vessels. After the roots of plants absorb water in the soil, capillarity allows the water to flow along the small vessels of the plant to all branches and leaves. It can be said that without capillarity, trees cannot flourish.


We can also observe the capillarity of plants through a simple experiment. Put the bottom of the celery stalk in a glass of water with food coloring and observe the movement of the color to the top leaves of the celery. It may take a few days. As shown in the picture below, even with the effect of gravity, colored water is still "attracted" upwards. The reason is that the capillarity of the small vessels in plants allows water molecules to move upwards.



In this project, we made an automatic watering device based on the capillarity of cotton rope. In further exploration, we also mentioned how to improve the efficiency of the automatic watering device by the enhancement of capillarity or the reduction of water evaporation.

The project is going to an end, please remove cables, and put all the BOSON modules back into the original positions of the kit.

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