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How to grow food without soil or sunlight? Middle school girls learned about technology in vertical farming.

By Qingwu (William) Meng

Last Saturday, I presented at the Middle School Girls Math and Science Day, held on the Michigan State University campus. Middle school girls participated in a variety of STEM-based activities. As a science advocate, I was glad to be part of this event for science outreach and gender equality. My activity was “growing food without soil or sunlight”, underpinning two crucial aspects of indoor farming. I first introduced hydroponics and then transitioned to LED lighting for plants. Curious middle school girls and their parents gathered around my self-built vertical growing system and asked lots of great questions. The following are a few highlights of my activity.

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I showed the participants how water circulated in a hydroponic system, which conserves tons of water compared to field irrigation. They touched and felt the rockwool substrate, on which seedlings reside and grow. They told me it was “fuzzy”, “wet”, and “spongy”. These adjectives described exactly why such a substrate, made from recycled fibers, could replace soil. Soil serves two purposes for plants. The first is to provide physical support for plants to grow upright. The second is to hold nutrients in water retained between soil particles. Since the rockwool substrate is sturdy and spongy enough, it can serve the same purposes. Also, it does not get messy like soil. With an understanding of the soilless medium, all of the participants transplanted seedlings in rockwool cubes to the hydroponic system. They were surprised that it would take only 4 weeks to harvest mature lettuce. Some told me they would try growing lettuce and basil this way in their kitchens.

Now that the plants are under multicolored LED lights, I continued to show them the power of light on plant growth. First up was photosynthesis, which I started with a question, “why are leaves green?” Many girls took brave guesses, and a couple of them were close to the correct answer. Chlorophylls and carotenoids are important pigments for photosynthesis. They mainly absorb red and blue light, reflecting green light back into our eyes, so we perceive leaves as green. Second, I moved onto coloration and played a time-lapse video of lettuce changing from green to red in two days with the help of UV and blue light. We put on sunscreen to prevent sunburn, and similarly, plants produce certain pigments as their tan to prevent radiation damages.

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On the subject of light, I discussed the advantages of LEDs: energy efficiency, long lifetime, and changeable colors. Rather than sunlight, we can use specific colors of LEDs because plants only use a small portion of the sunlight spectrum, mainly the visible part with red, green, and blue light. Most plants grow just fine under red and blue LEDs. However, adding green, far red, and UV can sometimes bring out desirable growth, shape, color, and even flavor. I then raised a question, “what color is it if you mix red, green, and blue light?” Some girls guesses brown or purple. I invited a couple of curious minds to mix these colors of light using a computer program. My LED array has a total of 7 different colors, which are independently controlled in this program. The girls first turned up red and blue light bars, and the result was pink or purple. As they finally added green, they were surprised to see white. They just discovered the RGB model to create white light. I held a piece of white paper close to the LED array, and they could see individual red, green, and blue colors. However, as I gradually moved the paper away from the LED array, these colors of light overlapped and diffused, creating a uniform white color. I told them such a broad spectrum as white light is not only useful for plant growth, but provides an ideal working environment, allowing easy detection of any issues on the plant.

Finally, I showed them how to create a dynamic light environment for plants. The girls excitedly used the program to change light colors and intensities based on various wave forms. The video below is their achievement. Of course, such rapid fluctuation is not practical, but it shows the capability to deliver different light regimens through different plant growth stages.

It was overall a rather rewarding experience to increase girls’ interest in plant science and horticultural lighting. They were highly engaged throughout my activity. It made my day to hear a girl telling her friend that this was her favorite activity. I am sure they will keep nourishing their curiosity and strive to excel in STEM fields.

Teaching middle school girls science