Hydroponics: Gardening Without Soil

Making your Hydroponic Containers

1. In this project, you will try hydroponics—the process of growing plants without soil. In hydroponics, the plant grows in a medium that retains moisture but does not contain nutrients. The medium provides structure for the plants. If you are using coconut coir as the growing medium, prepare it by adding filtered or purified water to the coconut coir brick as directed on the package. This loosens it so it can expand. Soil and coconut coir may look similar, but soil contains nutrients a plant needs to grow, and coconut coir does not.
   
   
   
   Figure 2. Brick of coconut coir in the process of loosening up.
   
   
2. Start by creating hydroponics containers from the empty, clean two-liter soda bottles. Repeat steps 3-8 six times so you have six identical hydroponics containers. The video can also guide you in building the containers.

Hydroponics in a 2-Liter Soda Bottle – STEM activity.

https://www.youtube.com/watch?v=87A06gzcZZ0

3. Use the permanent marker to draw a line around the bottle just below where the cylinder starts to curve in towards the cap.
4. Cut the bottle along the line with your scissors or utility knife.
   
   
   
   Figure 3. Cut the top of a two-liter plastic soda bottle to transform it into a hydroponics container.
   
   
5. Flip the top upside down and rest it in the larger bottom part of the bottle. You will grow your plant in the upside-down top part, and the bottom part of the bottle serves as a reservoir to hold the water.
   
   
   
   Figure 4. Two-liter plastic soda bottle in the process of being transformed into a hydroponics container.
   
   
6. A wick will transfer nutrient-rich water from the reservoir to the roots of the plant. To create the wick, knot the two cotton or felt strips together at one end.
   
   
   
   Figure 5. Cotton strips knotted together will be used as the wick.
   
   
7. Push the loose ends through the bottle top so they hang down into the reservoir. The knot should stop the wick from going all the way through—if it doesn't, retie a larger knot.
   
   
   
   Figure 6. The knot in the wick keeps it in place.
   
   
8. Place the top with the wick back into the bottom bottle. Your hydroponics container is ready.

Preparing Data Collection

9. Prepare your data table in your lab notebook. Table 1 is an example table you can copy.

Setting Up the Hydroponic Experiment

10. You will grow plants in six containers. You will nourish half of them with nutrient-rich water and the others with plain purified or filtered water. You will prepare the containers, seed and treat all plants in the same way. The only difference will be the type of water you provide to the plants. Do you expect one group to grow more vigorously than the other? Why? Write your expectations down in your notebook.
11. Fill the growing area of all six containers with the growing medium. A growing medium in hydroponics is inert, meaning that it does not contain nutrients like soil. It is used to hold moisture and provide structure to the plant. Be sure to pull the wick up about 2/3 of the way into the growing medium. This will ensure that the water and nutrients stored in the reservoir reach the plant's roots.
    
    
    
    Figure 7. Hydroponics container ready for seeding or planting.
    
    
12. Seeds can germinate in coconut coir but not in clay pebbles; you will need a rooter plug or soil plug for germination if you use clay pebbles.
    • If you are using a plug: place three seeds into the plug and place the plug just above the knot in the wick.
    • If you seed in coconut coir, place three seeds in the coconut coir just above the knot in the wick.
    Cover the seeds with growing medium (seeds germinate better when in the dark).
13. Record the data of seeding in your lab notebook (top row of your table like Table 1).
14. Use your permanent marker to mark three containers with 'N 1', 'N 2', and 'N 3' respectively. These containers will receive nutrient rich water.
15. Mark the other three containers with 'W 1', 'W 2', and 'W 3' respectively. These containers will receive plain filtered or purified water.
16. To prepare the nutrient-rich water, measure 1 quart of bottled, filtered, or purified water into your second bottle or container. Avoid unfiltered tap water as that can contain contaminants that may inhibit your plants' growth.
17. Look at the label of the liquid nutrients bottle to find out how much of the solution you need to add to a quart of water in the growing phase of the plant. Mix that into the water in your second bottle or container. Your tiny plants will not consume much, so the water you prepare now will last until the plant is somewhat larger.
18. Record the recipe for nutrient-rich water that you used in your lab notebook.
19. For the three containers marked with an N for nutrient-rich: pour the prepared water over the growing medium. It will seep into the reservoir. Keep pouring until the reservoir is about 1/2 to 2/3 full. The water should never reach the spout of the bottle. Make sure that the area around the seeds gets wet as you pour the water.
    
    
    
    Figure 8. Hydroponics container of which the water reservoir is filled.
    
    
20. For the three containers marked with a W left with an empty water reservoir: repeat step 19 using pure purified or filtered water.
21. Optional: the reservoirs can stay exposed to sunlight, but algae will grow and turn the water green. This will not hurt the plant, but it will not look very pretty! To prevent this, you can cover the reservoirs with aluminum foil.
    
    
    
    Figure 9. Hydroponics container wrapped in foil.
    
    

Conducting the Hydroponic Experiment

22. Seeds can germinate in the dark, but once they emerge above the soil, plants need air and sunlight to survive. Once the seed is sprouted, place the container near a window (preferably south-facing or west-facing, so the plants receive plenty of sunlight) and wait. If natural sunlight is unavailable, use a grow lamp to provide light for the plants.
23. For the first couple of days, check daily to make sure the area around the seed or tiny plant is moist. Add a little purified or filtered water if needed. As the plant grows, its roots will extend deeper and get better access to the water (for the plants that only receive plain water) or water and nutrients (for the plants that receive enriched water) sucked up by the wick.
24. If you see sprouts peak out, check the container's label and mark the date in your table, like Table 1.
25. Once you see clear leaves:
    • Measure the largest leaf seen in each container and note its length (in millimeters) down in your data table like Table 1.
    • Count the number of leaves for the plants in this container and note it down in your data table.
    • Do not forget to write down the date you did the observation.
    Repeat this every couple of days.
26. Once the plant is established, check the water level in the reservoir weekly. If you use aluminum to cover the reservoir, you will need to remove it to check the water level. If it runs low in a container, check if this container is marked with an N for nutrient-rich.
    • If the container is marked: Make a new batch of nutrient-rich water and add it. Check the directions that come with the nutrients—you will probably need to add more nutrients for the same amount of water once the plant is well established.
    • If the container is not marked: Add filtered or purified water.
    Notice that it is ok to fill the water reservoir up early. You do not need to wait until it is almost empty!
    
    
    
    Figure 10. Plants growing in hydroponics containers made from 2-liter soda bottles.
    
    
27. Keep monitoring, measuring, feeding, and watering your plants for about 3 to 6 weeks, or until some plants are well developed.

Analyzing Your Data

28. Gently uproot the plants and carefully remove and wash the medium from the roots. Carefully dry the plants between paper towels. Write the container label on the paper towels so you always remember whether this plant received nutrients.
29. Some variables you can study are:
    • Using the digital scale, weigh the uprooted plants.
    • Observe the color of the roots for the plants. Are there differences between those that received nutrients and those that did not?
    • Weigh the roots separately. Did plants receiving nutrient rich water develop more, less or about the same mass of roots?
    • Look at the number of hairs that you see on the roots for each plant. Root hairs enable a plant to take in water and nutrients.
    • Trace the largest leaf found on each plant on millimeter paper. Count the squares it covers; this quantifies the area of the leaf.
    Make a new table like Table 2 in your notebook to store your data.

30. If you have numerical values (like the weight), calculate the average for each group.
31. Can you present this data graphically?
32. Review the data that you collected during the growth to see if you can conclude something about the growth of plants that received nutrient-rich water compared to those that received plain water. Choose the number of leaves together with one of the following variables to study:
    • The length of the largest leaf.
    • The width of the largest leaf.
    • The estimated area of the leaf. To calculate the area of the largest leaf for each container on each day that you made measurements, you may have to make an estimation about the shape of the leaf. Separate the shape of the leaf into two shapes, like an ellipse, or oval, and a triangle, as shown in Figure 11. You can estimate the area of the leaf by calculating the area of the oval and adding the value to the area of the triangle. If you would like some additional information on calculating the area of common shapes, refer to the Bibliography. For the uprooted plants, you can also trace the leaves on millimeter paper and count the squares it covers.
    
    
    
    
    Figure 11. This image gives an idea of how to estimate the area of a leaf using an ellipse (oval) and a triangle.
    
    
33. Rewrite your collected data in two tables, one for each variable you will study in detail. Calculate the average for each group (the group that received nutrients and the other that did not receive nutrients). Table 3 is an example table that has been partially filled in. Your data will be different!

34. Plot the average number of leaves. Label the x-axis 'Day' and the y-axis 'Average number of leaves'. Plot the averages for plants receiving nutrient-rich water in one color. In a different color, plot the averages for plants receiving plain water. Make your plots by hand or online. For help creating plots online, try the Create a Graph website.
35. In a similar way, plot the average of the other growth variable you studied (length, width, or area of the largest leaf).
36. Look at your tables and graphs. Do they show a difference in the average growth of the two groups of plants? Is there a difference in the weight and in the number of root hairs between the two groups? Can you conclude that one group grew more vigorously than the other, or is your data inconclusive?
37. Seeing your data, do you conclude that growing plants hydroponically in nutrient-rich water is a good choice? Is it better than growing plants hydroponically in plain water?
38. Now that you have done the experiment, are there unanswered questions you would like to study? Are there parts in your experiment you would do differently if you had to do the experiment all over again?