How YOU Can Do Hydroponics

Lesson Plans

Design an Experiment

Mix a Nutrient Solution

Set Up the Experiment

Let it Grow and See What Happens

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Lesson Four: Set Up the Experiment

Step One: Assemble the Hydroponic Apparatus

This type of hydroponic apparatus, known as a wick system, is one of the easiest ways to grow things hydroponically. It does not require a pump; it draws the nutrient solution up to the plants' roots by capillary action in strips of felt. You will need to build at least one hydroponic apparatus for every different type of nutrient solution you are using.

Materials needed per hydroponic apparatus:

one plastic container, about 12 x 7 x 5 in.
two little pots, about 4-4.5 in. diameter
four strips of white felt, about 3 x 6 in.
two thin boards, about 2 x 8 in.
shrink wrap, plastic wrap, or other waterproof covering
sharp knife
Perlite

First, prepare the platforms on which the pots will sit. Wrap each of the thin boards with the shrink wrap or waterproof covering. Seal it with tape if necessary; the board needs to be as waterproof as possible. If you do not do this, the nutrient solution will soak into the board and soften the wood, causing the board to bend, lower the pot deeper into the solution than it should go, and possibly break.

After the boards have been waterproofed, you should thoroughly wash the boards, plastic container, and pots with soap and water. Then disinfect them by rubbing them down with rubbing alcohol or another chemical cleaner such as Lysol. This kills any microorganisms living in your equipment that could infect your plants.

Diagram of bottom of pot Cut two long, narrow slits near the outer edge of the bottom of each pot as shown in this diagram. Pull the strips of felt through each slit so that they are about half in the pot and half underneath the pot. Place each pot on a shrink-wrapped platform so that one strip of felt hangs down on one side and the other strip hangs down on the other. Then place both platforms on top of the container so that they hang across the container. Fill each of the pots about 2/3 full with Perlite; be aware that some may leak out through the slits in the bottom of the pots. Label each hydroponic apparatus with the type of nutrient solution it will contain.

Diagram of hydroponic apparatus

Step Two: Create Appropriate Growing Conditions

Plants will grow best when they are subject to certain conditions. While it is best to keep conditions consistent throughout the experiment, certain conditions are hard to control and may fluctuate. The important thing is that the conditions must be the same for all the plants at any given time, regardless of how they change over time, because they are controlled variables in the experiment. The easiest way to keep the controlled variables under control is to put all the plants next to each other in the same location. Note that you can do an experiment by varying one of these conditions. However, if you do that, you must use the same nutrient solution for all the plants and keep all the other conditions the same. This keeps your experiment from having more than one independent variable.

Light:

You should make sure your plants get around twelve hours of light. This is not exact; a few hours more or less will probably work fine. Since plants get their energy from light, they must have exposure to the sun. However, they should probably not get light 24 hours a day because such unnatural conditions may disrupt the normal growth of the plant. You may also substitute a grow light for natural sunlight; be sure to put it on a timer to simulate day and night for your plants.

Temperature:

Ideally, the temperature should be somewhere between 55° F and 85° F. The optimum temperature may be different for different kinds of plants. A temperature-controlled environment would provide the most stable conditions, but if your plants are in a less stable environment, a heater would help to keep the temperature under control. If the environment gets too hot, you might want to shade your plants and/or put ice cubes in their nutrient solution to keep them from dying in the heat.

Humidity:

The relative humidity must be at least 45%, and ideally it should be between 60-75%. This can be hard to control, but if you know your air is dry, your plants will benefit from some artificial humidity. This can be done with a hoochie-coochie machine (a silly word that means a vaporizer). The hoochie-coochie machine will make water vapor more slowly when the air is relatively humid already, so it would not be a bad idea to leave it on all the time. Another way to raise the humidity is to spray water all over the place with a hose or spray bottle. However, this has the undesirable side effect of soaking everything around your experiment which you may not want to get wet.

(Note: The term "hoochie-coochie machine" was coined by Miss L, our AP Biology teacher who could not think of the word "vaporizer." No members of S.H.A.R.P. were responsible for this. We used it on our web site because we think it's kind of funny to say.)

Other conditions:

Factors such as ambient noise, air quality, etc. can also influence the growth of plants. Be sure to keep all other such variables controlled for all your plants.

Source for this section: Casana, Maritza. maritza_casana@hotmail.com. "Práctica de producción de hortalizas bajo la técnica de hidroponía en agua y perlita." 7 Jan 2001. Personal e-mail. (14 Jan 2001).

Step Three: Germinate the Seeds

Before you germinate the seeds, you must choose what kind of plant you want to grow. If you already have a plant growing in soil and you want to simply transfer it to a hydroponic medium, you can skip this step. If you are growing from seeds, you need to choose what kind; we recommend lettuce, beets, tomatoes, celery, and obviously radishes. Other kinds of plants would probably work well too. Note the growing time listed on the package of seeds you use; it determines the length of your experiment. Ideally, you should use seeds with the shortest growing time possible. You should also allow lots of extra time in your experiment in case the plants grow slowly or something else goes wrong.

Source: Casana, Maritza. maritza_casana@hotmail.com. "Práctica de producción de hortalizas bajo la técnica de hidroponía en agua y perlita." 7 Jan 2001. Personal e-mail. (14 Jan 2001).

Cherry Belle Radish seeds

Materials needed:

seeds
clean petri plates
paper towels or cotton balls
spray bottle

You will need to use enough petri plates to hold the amount of seeds you want to germinate. You should germinate at least twice as many seeds as you want to actually grow because some of the seeds might not germinate and some of the plants might die.

Instructions for each petri plate:

Line the petri plate with a layer of cotton balls or paper towels. Place the seeds on the cotton or paper towels in the petri plate, leaving about 1 cm of space between them. You may want to leave even more space for larger seeds. Spray the petri plate with water using the spray bottle until the cotton balls or paper towels are throughly soaked. Put the lid on the petri plate and leave it in the sun for the seeds to germinate.

Put a rubber band around the petri plate to hold the lid on tightly. This keeps the petri plate from falling apart if someone knocks it over by accident. It also keeps the petri plate from opening when the seeds germinate and the little plants get so big that they push on the lid. If the lid opens, the water will leave the petri plate and the little plants will dry out and die. (The members of S.H.A.R.P. learned this lesson the hard way.)

Step Four: Plant the seeds in Perlite

When the seeds have germinated and the little plants are about 1.5 inches long, you should remove them from the petri plates and plant them in the Perlite in your hydroponic apparatus. Before you do this, you should prepare the nutrient solutions in your hydroponic apparatus. Do this as described in Lesson Three: Add the appropriate amount of each concentrated part to the 2-Liter mixing bottle and fill the bottle to the top with deionized water. Then pour the contents of the mixing bottle into the plastic container in your hydroponic apparatus. You will probably need to mix more than one bottle of each solution to fill the container; the container should be filled as high as possible without spilling the nutrient solution.

Before you finish filling the container, pour some of the solution in each pot with Perlite on each of the felt strips. This "primes" the felt strips so their capillary action is more effective. You may also want to save some nutrient solution to pour on your plants after you plant them in the Perlite.

When the nutrient solution is ready in the containers and has been poured through the Perlite and the felt strips, you are ready to plant the little plants. Plant four plants in each little pot with the roots submerged in the Perlite and the shoots poking up toward the light. Plant the plants fairly close to the felt strips so they have easy access to nutrient solution, but do not plant them closer together than about one inch. You may want to save any extra plants you have by growing them in soil or in more Perlite somewhere else in case something goes wrong with the plants you have planted.

Check the environmental conditions to make sure they are appropriate: Make sure the plants are getting about twelve hours of light (give or take a few) from the grow light or the sun. Make sure the temperature is between 55-85° F. Make sure the relative humidity is at least 45% and ideally between 60-75%. Your experiment is now set up and going!