Science Project:

Heating Plants: The Great Growth Race

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Materials:

  • 6 Paperwhite bulbs
  • 6 small plant pots
  • Potting soil
  • Pea gravel
  • Plant sprayer
  • Notebook
  • Pencil
  • Ruler
  • Pen
  • Permanent marker
  • Two grow lights on stands
  • Masking tape

Procedure

  1. Put about an inch of pea gravel into the bottom of each pot.
  2. Place the plant bulb on top of the pea gravel. Make sure the roots are on the bottom.
  3. Place potting soil into each pot until the level of the soil is about half an inch below the top of the pot.
  4. Use the spray bottle to mist the soil.
  5. Your bulbs are ready to go! Place a strip of masking on each pot as a label.
  6. Use a permanent marker to write "cold" on two of the masking tape labels, "hot" on another two, and "warm" on the last two.
  7. Take your cold and your warm pots to a cool space like a garage or outdoor shed.
  8. Place one of the grow lights in the cool space, overlooking the four pots.
  9. Take your two hot pots and place them in a warm area indoors.
  10. Place the remaining grow light over these two pots.
  11. Think about what you know about plants and temperature. Do you think heat is an important factor in a plant's growth? Can a plant have too little heat or too much heat?
  12. Consider this experiment's problem: Will heat affect a plant's growth rate? What do you think? Write down your guess, or hypothesis, in your notebook.
  13. Carefully watch your plants over the next few days. Keep them moist with your spray bottle and make sure the grow light is on at least eight hours a day.
  14. Remember to be patient: you will be observing these plants for about four to six weeks. Make sure you measure and record the height of each plant every three days.
  15. At the end of the first week, move the two warm pots from the outdoor cool space to the indoor warm space.
  16. After the second week, move the two warm pots back to the outdoor cool space. Keep alternating the warm pots back and forth for the duration of your experiment.
  17. At the end of the four to six weeks, be sure to record a final measurement for each plant. Which plants grew the fastest?

Results:

Bulbs planted in the extremely cold or extremely hot places should have grown the slowest. The fastest growing bulbs were the warm ones that alternated between the cold and hot temperatures.

Why?

Do you remember the story of Goldilocks and the Three Bears? You may be surprised to realize that this heating plants experiment actually parallels the silly adventures of Goldilocks as she tried porridge that was first too cold, then too hot, then -- finally -- just right. The bulbs in the cool space were, of course, too cold, but the bulbs inside your house were actually too hot. Only the bulbs that got to go back and forth grew "just right." Paperwhite bulbs, like other plants, need light, water and heat to grow, but they need a very specific amount to truly thrive. If you tamper around too much with a plant's overall temperature, you hurt its growth rate.

Now you know that different temperature levels affect a plant's growth -- what about different levels of light or water? Try this same experiment, but compare how much water a plants gets or how much light it has access to. Don't forget to make a hypothesis whenever you conduct an experiment! Guessing and testing is an essential part of every scientist's experiment process -- why not make it an essential part of your experiment process too?

Author: Tricia Edgar
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