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ACTIVITY: Build a Hydroponic System!

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. The roots of hydroponic plants grow in water.</p>

Phenomenon:

Plants can be grown in water—without any soil (Fig. 1)!

 

Inquiry:

Can plants thrive without soil?

 

Guiding Questions:

  1. What do people/animals need to grow?
  2. How are plants different than animals?
  3. What are the main things that plants need to grow?

Activity:

Build a hydroponics system and compare plants grown without soil to those grown in soil.

Note: Hydroponics is the method of growing plants in water (without soil). In comparison, Aquaponics is a system that combines aquaculture (the growing of aquatic animals, like fish, snails, clams, etc.) in combination with hydroponically grown plants.

Note to teachers:

There are many ways you can build a hydroponics system. The system described below is a simple one, but it can be adapted for bigger or more complex arrangements. To combine this hydroponics activity and aquaponics in a bottle into one longer-term activity, click the activity extension for instructions. The procedure outlined there will guide you through creating an alternative hydroponics design that is adaptable to convert into an aquaponics system.


Materials:

  • Student worksheet and teacher guide (attached below):

  • Container to hold water
  • Optional: black spray paint and painters tape <p>Fig. 2. Black cinder works well as a root structural support for a hydroponic system.</p>
  • Thick piece of square foam (e.g. Styrofoam)
  • Plant food, 1 box per class – nutrient additive such as MiracleGro (tomato plant food generally has the right proportions of nutrients and will do the trick).
  • Root structural support (e.g. cinder (Fig. 2), gravel, wood fibers, perlite, vermiculite, pumice or grow stones).
  • Aquarium aerator, with tubing and airstone.
  • Small plastic pots or waterproof mesh containers
  • Optional: pH test kit (1 per class, available at pet stores).
  • Basil (1 or 2 plants with roots per group plus an extra plant that will stay in the soil).
  • Ruler
  • Access to water to keep your system filled
  • Counter or table space with sunlight for growing the hydroponic plants

Note to teachers: 

  • This activity requires care and maintence over time; it may take two weeks 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 types plants.


Procedure:

  1. Follow along on your worksheet to grow your plants hydroponically!
  2. Start with enough basil plants (ones that have roots and are already growing) for groups to create different grow condition treatments (1 or 2 plants per group).
  3. Keep 1 or 2 plants in soil and place them next to, or near, your hydroponic systems (so they can grow in similar light conditions). This will be your 'control plant' and will provide a comparison to the hydroponic plants at the end of the growth period. Don't forget to water both the control and the treatment plants over the experimental period (Fig 3A & 3B)!

<p>Fig 3A. Basil and cilantro growing side by side in a hydroponic system. Comparing plants grown hydroponically to those grown in soil can be helpful to explore what plants need to grow.</p><br />
<p>Fig 3B. Basil grown in soil. A plant in soil may grow at a different rate than one in hydroponics.</p><br />


Prepare your water container and mixture

  1. Optional: if it is not already black, you can paint the outside of your water basin to help prevent algae overgrowth. Using painters’ tape, block of the top inch of the container and paint the bottom (so the top remains clear and you can observe the water level) (Fig. 4A & 4B).
    Note: You can leave the container clear! Doing so will allow students to see root growth, however a clear container may require extra cleaning to remove algae growth.

<p>Fig. 4A. If you choose to paint your container, prep it by taping off a top section so you can see the water line.</p> <p>Fig 4B. Spray paint it black to prevent algae overgrowth as your system matures.</p>


  1. After the paint is dry, fill the container with water just above the black line, leaving space for displacement when you add the plants. Be sure to place your system near an outlet if you are using an aerator airstones.
  2. Stir in a teaspoon of plant food and allow it to dissolve.
    Note: The amount of nutrients added might need to be adjusted based on the size of the water basin. Follow instructions on plant food packaging for assistance.
  3. Plug in the aerator and place the stones in the water mixture. 

Prep your plants

<p>Fig. 5. Holes in your plant container will allow for water flow and help roots grow long and healthy.</p>

  1. If you are using small plastic pots that don't have holes, drill holes to allow for water transfer (Fig. 5).
  2. Trace the bottom of the hydroponic pots on the foam.
    Note: Don’t space the holes too far apart or the edges of the foam will sag and your pots will not float evenly!
  3. Cut out the circles in the foam. You will need to cut a little wider than the traced circle to allow the pots to sit low enough in the water.
  4. <p>Fig. 6. Almost ready to grow your plants!</p>Fill the hydroponic pots with about an inch of root structural support, such as black cinder or gravel, on the bottom of the containers (Fig. 6).
  5. Remove the basil plants from their starting pots, gently removing soil from around the root structures.
  6. Place the plants in the hydroponic pots so the bottom of the roots touch the bottom of the pots, and fill in the remaining space with more cinder so the plants can sit upright.
  7. Put your hydroponic pots into the holes of the foam. Allow about an inch or two of the pots to be exposed below the foam—this lower two inches of the pot will be submerged in the water.
  8. Place your hydroponic pot and foam combination in your water container and allow them to grow!

Care for your system

  1. <p>Fig. 7. Your plants will blossom in no time!</p>Water will evaporate over time, so you will need to refill your container. Every time (or every other time!) that you refill, add more nutrients to keep the plants growing well.
  2. Optional: Use your pH test kit to check the pH regularly. This will help ensure your system is stable. Basil likes a pH of about 6.5-6.8, so you can adjust as needed using your pH up or down bottles in the test kit. 
    Note: If you are making your own nutrient solution rather than using plant food, review Perfecting the pH of your Hydroponic Nutrient Solution.
  3. Let the plants grow (Fig. 7)!
  4. Measure your plants' growth, and record your results in the data table on your worksheet. Use a consistent method to measure, for example:
    1. Place the bottom of the ruler at the base of the plant and measure to the tip of the main stem.
    2. Count the number of leaves, or choose a leaf to measure each time.
  5. Compare these results to the plant grown in soil only. 


Activity Questions:

  1. What happened to your best growing plant during the experiment?
  2. Where did your plant get its energy to grow?
  3. What resources did you give your plants?
  4. Compare the basil grown in soil versus the one grown hydroponically:
    1. Describe how your hydroponic plant grew.
    2. Describe how your plant in soil grew.
  5. Collect the class data for plant growth:
    1. What was the class average hydroponic plant growth height (inches)?
    2. What was the class average soil plant growth (inches)?
  6. How does your data compare to the class average?
  7. Did the plants need soil to grow? What evidence do you have?
  8. Why do you think plants normally grow in soil?
  9. What do you think soil provides to plants?
  10. How are hydroponic plants surviving without soil?
  11. Aquaponics is a system that combines aquaculture (the growing of aquatic animals, like fish, snails, clams, etc.) in combination with hydroponicly grown plants. In aquaponic systems, growers do not need to add nutrients (like you did in this hydroponic experiment). Explain why aquaponics systems do not need added nutrients.

Further Investigations:

Experiment with different types of plants:

  1. Follow the procedure above with other varities of plants. Some others that can be good for hydroponic growth include: <p>Fig. 8. Other plants, such as lettuce shown here, can also grow well in hydroponic systems.</p>
  • Greens such as lettuce, spinach, Swiss chard, and kale.
  • Herbs such as parsley, oregano, cilantro and mint
  • Tomatoes
  • Strawberries
  • Hot Peppers

 

  1. Explore similarities and differences between plant species and answer the following questions:
  1. What did you notice about the plants as they grew?
  2. Which plants grew best in hydroponics?
  3. What things did you have to adjust, or might adjust in the future, to accomadate different plants?
  4. What were the main things ALL species of plants needed?

Experiment with different variables:

  1. Manipulate variables: After you have built your hydroponic system described above, play around with different variables to see how plant growth may change. Continue to care for them i.e. giving nutrients and ensuring appropriate water levels.
    1. Light: arrange plants so they recieve different levels of light. Place one directly in front of the window for ample sunlight. Allow the others to grow in more shaded areas.
      1. What did you notice?
      2. Which level of light was the most desirable?
    2. Carbon Dioxide: Using recycled materials, such as a clear 2L plastic soda bottle, create a covering to place overtop of your growing plant. Have students breath into it to increase the amount of CO2 that the plant is recieving. Design a schedule so the plant getting extra CO2 recieves it multiple times a day.
      1. What did you notice?
      2. Did the adjusted CO2 levels influence the plant growth? 
      3. If so, which level of CO2 helped the plants grow biggest?
      4. If not, why not?
    3. Nutrients: Adjust the levels of nutrients you are feeding your plants. Keep a consistent schedule so each plant recieves it's designated amount. FOr example, plant (A) may recieve a half table spoon, plant (B) may recieve a full table spoon, and plant (C) may get 1 and a half tablespoons. Refer to the instructions on the box of your nutrient additive and adjust up and/or down according to the specific plants needs.
      1. What did you notice?
      2. Which amount of nutrients made the plant grow biggest?
      3. What does this tell you about the main things that plants need to grow?
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.