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ACTIVITY: Can Plants Grow Without Soil?

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

The activity below draws from the content in the page Materials for Plant Growth

<p>Fig. 1. This plant has been growing only in water for almost a year!</p>Phenomenon:

Plants can grow without soil (Fig. 1)!

Inquiry:

What do plants need to grow?

Guiding Questions:

  1. What do you think plants need to grow?
  2. What do plants get from the soil? 
  3. What do plants get from the air? 

Common Misconceptions About Plant Growth:
  • Students may not recognize that there are components in the air that plants need to grow. Plants use the carbon from CO2, combined with water, to build their body mass.
  • Students may think that plants need soil to build their body mass. This is especially complicated because animals get the building blocks they need from food, which is visible. Soil is also visible, and many plants are rooted in soil, so it is natural for students to think the bulk of plants' bodies comes from the soil. Many plants do get stability from rooting in the soil, and often plants also get nutrients and water from soil, but nutrients and water can come from sources other than soil.

Activity:

Establish a simple system to grow plants in water. Then, manipulate other variables to explore what affects growth.


Materials:

  • Student worksheet and teacher guide (attached below)

  • Basil plant clippings
  • Recycled 2L bottles (2 per group)
  • Small glass cups (2 of the same size per group)
  • Scissors or knife (teacher supervision required to cut hole in bottle)
  • Ruler
  • Permanent marker
  • Mesh material (for shade cloth; can use cheesecloth)
  • Nutrients (e.g. plant food such as miracle-gro from hardware store is fine)
  • Metal or silicone straw

Teacher Recommendations:

  • This activity set-up forms the basis of an experiment to determine what factors influence plant growth. From here students will manipulate variables and compare what plants need to grow. Student groups can conduct different trials and compare results with the rest of the class. You may want to demonstrate your own version first and use that set-up as the control, with no manipulations, which can then be used to compare with the student results.

  • Each group may conduct all three trials, or you may split the trials so that each group does one trial.

  • If there are many groups, more than one group can also conduct the same trial, exploring the same variable. This creates replicates, an important componant in scientific studies.


  • <p>Fig 2. A world wrapped in plastic is not a healthy world. Avoid using single use plastics when you can, and if it canʻt be avoided, re-use and recycle it.</p>In an attempt to limit single use plastics, this activity is written to encourage recycling efforts. A student assignment could be to find used soda bottles to re-use for this activity, and discussions could incorporate the importance of re-using and recycling (Fig. 2). 
  • This activity requires care and maintence over time, as it may take two weeks or more to see ample plant growth.
  • The following instructions are written for the use of a basil plant because they grow quickly and easily. Further investigation could be conducted to grow different plants.
  • This activity is designed to be the first of a series of activities to explore this performance expectation. The activities Build a Hydroponic System and Aquaponics in a Bottle build on this base understanding. 

Procedure:

Set up your experiment!

  1. <p>Fig. 3. Measure the basil from base to tip of the stem, ignoring leaves.</p>Use a ruler and scissors to cut your basil clippings so they are the same size. Measure from the base to the tip of the stem, without including leaves (Fig. 3).
  2. Write down the length of your basil clippings on your data sheet.
  3. Add about an inch of water to the bottom of both glasses. Be sure both cups have an equal amount of water.
  4. Draw a line on the glass to mark the water level. As water evaporates over time, refill water up to the line.
  5. Place one basil clipping in each glass so the base of the stem is submerged (Fig. 4).
  6. Cut the top off of your recycled 2L bottles to create the ʻgrow domesʻ for your plants.
  7. With help from your teacher, cut a small hole in the side of each grow dome. Clean the domes.
  8. Place a 'grow dome' upside down on top of each of your two basil plants (Fig. 5).

<p>Fig. 4. Can basil clippings in a glass of water continue growing?</p><br />
<p>Fig. 5. Model 'grow-domes' with a hole for a straw.</p><br />

​Perform your manipulations!

  1. Label each glass and corresponding grow-dome A or B. 

    1. You will apply manipulations to the plant labeled A.

    2. Leave plant B alone to grow as your contol.

    3. Don't mix them up!

  2. ​Allow both plants to grow under the 'grow domes.'
    1. Keep the water levels at the line drawn on each glass.
    2. Measure plant A and B periodically and write the heights on your data sheet.
  3. Conduct trials to manipulate the three variables of carbon dioxide (CO2), nutrients, and light:

Trial #1: Extra CO2

  1. Using the metal or silicone straw, blow into plant A to add CO2.

  2. Set up a schedule so you can add CO2 as often as possible at regular and consistent intervals

Trial #2: Extra Nutrients

  1. Follow the instructions on your plant food mixture to add nutrients to plant A at regular intervals. Once a week should be fine, but you can also experiment with different intervals.
    Note: Keep in mind, your plants are not in very much water, so be sure you don't add too much of the nutrient mix!

Trial #3: Limit Light

  1. Place the mesh cloth over plant A to limit the amount of light available. Tape it down so it stays in the same position for the whole experimental period.
    Note: You may need to double up the mesh cloth or use a different material to limit the light more fully. 
  2. Let both plants grow for the designated time, ensuring they both have enough water. 

Activity Questions:

  1. What variable did you test in your experiment?
  2. Which of your plants (A or B) grew more? By how much? 
  3. What else did you notice about the structure of your plant? Describe the growth of both plants. (Hint: look at other structures like the roots or leaves (Fig. 6A and 6B).)

<p>Fig. 6A. It's important to observe different aspects of plant growth in your experiment.</p><br />
<p>Fig. 6B. How do the root structures differ between treatments?</p><br />


  1. If another group looked at the same variable, how do your results compare to theirs?
  2. Compare the results across the three variable trials: CO2, nutrients, and light. (Hint: did you observe differences in plant health, root structure, stem growth, quantity and/or color of leaves, etc.?)
  3. What variables contribute to plant growth? Use data from your class' experiments to support your statement.
  4. Why is it important to control as many variables as possible in an experiment? (Hint: why did each trial look at only one variable? Why did each trial have a control (plant B)?)
  5. What are the minimum requirements that plants need to grow?

Further Investigations:

  1. Grow your plant as fast as possible: Using data from your class trials, combine nutrients, CO2, and light to grow your plant as fast as possible.
  2. What else do plants need: Choose another variable you would like to manipulate, make a plan, and explore that in an experiment.
  3. Explore your plant's need for water:
    1. Transplant your plants to soil. 
    2. Saturate both plants' soil with water.
    3. Continue to water plant B, but stop watering plant A. 

 

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.