Light is Life
- Describe why seedlings need light
- Identify alternative sources of light that would promote plant growth
Did you ever wonder why plants grow toward the light? Of course, we all know that plants need light for photosynthesis but why they actually reach for light is a bit less common knowledge. Plants contain a pigment called phytochrome which is a photoreceptor that reacts in a chemical way to light exposure. I guess you could say that phytochrome allows plants to “see” light and respond to it.
When plants have too little light they become “leggy”, that is to say, they grow more aggressively toward the light and take on that spindly look that often leads them to become weak and topple over.
So to prepare seedlings for maturity and to ensure that garden plants are well suited to the conditions of the garden or high tunnel, it’s important to provide them with enough light. Light enables the seedlings to develop a sound stem and leaf structure that will allow them to survive on their own.
Many gardeners use artificial lights to accomplish this in the early development of seedlings. LED lights are more expensive than traditional lighting but it offers a specific spectrum of light that is designed perfectly for growing indoors and they are more energy efficient as well.
Tools & Materials
- 3 small containers
- Grow light
- LED light
Introduction (10 minutes)
Begin the lesson by explaining how plants use light for photosynthesis and how phytochrome is the receptor for light allowing plants to “see”. This experiment demonstrates how they are affected by light using a Three Bears approach – one has no light, one has too little light, and the other has just the right amount.
Activity (20 minutes)
Prepare for this lesson in advance. Decide on a seed variety that you’d like to test and start them in a seed starting medium early enough to allow for germination and a few days of above-soil growth. The information on the seed packet will tell you how long it will take to germinate and pre-soaking the seeds in water for 24 hours before sowing will help. Start three sets of seeds. Three days before the lesson, move one container away from the light altogether, move one to the edge of the reach of the light, and leave one perfectly positioned under the light. The light should be used for 18 hours a day.
Discussion (10 minutes)
Is there a difference in the height of the starts? Do you notice anything different about each set? What role is light playing in their development? What do you think would happen if we moved all three containers back under the lights?
Assessment (5 minutes)
Use the following questions to assess the Students before and after the lesson. Tally the responses of the group in the Assessment Tracking Log for comparison:
- By a show of hands, how many of you know how light affects young seedlings?
- Now that you know how light affects seedlings, how many of you think you could manage seedlings in a way that allows them to receive the proper amount of light to develop?
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