Key Questions
* What do plants need to grow?
* Can plants grow without soil?

Time frame
* Teacher preparation will take approximately 30-40 minutes.
* During Part Two the project will be monitored for about five minutes a day over a period
* Part Three takes place after the monitoring period, and will require about 20 minutes.

Materials
For each child:
* 2 small yogurt (or cottage cheese) containers, one with a lid
* 15 cm of string or cotton, unwaxed
* 1/2-1 cup of growth culture (vermiculite, perlite mixture, or cotton balls) (amount of culture needed will depend upon the size of the carton)
* 1 cup of water
* 3-4 seeds (choose quick sprouters, such as lettuce, radish, or mung bean; if you are buying a package of seeds, check the expiration date stamped on the package.)

Materials for the class:
* paper towels (any type is fine)
* paper and pencil (or crayons)
* newspapers and sponges for clean-up

Materials for teacher:
* permanent marker or masking tape and crayons to label student projects (with masking tape and crayons students can label their cartons themselves)
* awl or other tool for putting a hole in bottom of each milk carton
* measuring cups for water (or water can be measured by students)
* nutrient solution (pre-mixed, commercial variety plant food "for vegetables"; with a medicine dropper-type cap is preferable)

For teacher demonstration:
* 1 small yogurt container (or cottage cheese containers) with a hole in the bottom and lid with a hole; or 1 milk carton with a hole in the bottom
* 2 yogurt containers (or cottage cheese containers or milk cartons), without a hole
* 1 cup of potting soil
* 1 cup of growth culture (of the type described for students)
* 6 seeds (of the type described for students)
* 1 mister or other container with water
* 1 potted plant (large enough to be seen by students)
* optional: tray lined with newspaper

Getting Ready
In the days before the class
1. Identify a place where student projects can be left safely , near sunlight, for up to a week.
2. Obtain all of the materials; wash the containers thoroughly.
3. In each of half of the containers, poke a hole in the bottom, so each student will have one container with a hole, and one without a hole. Make the holes big enough to slide a string through, but not so big that a knot in the string will slide through.
4. Cut the string into 15 cm pieces.
5. Tie a knot in the middle of each length of string.

The knot must be large enough to prevent the string from being pulled through the hole you made in the (top) milk carton.

6. You may wish to knot the string and push the string through the hole for younger students.
7. If possible, identify adults or older students to assist you on the day of the class.

On the day of the class
1. Wet the growing culture slightly, so that it is damp. If you can squeeze water out of the culture, it is too wet.
2. Organize the room so that students can work on their projects in groups of 4-6.
3. Prepare a demonstration tray, with the items needed to show students how to make their hydroponic systems (see illustrations above).
4. Set aside the rest of the materials so they do not attract attention prior to the activity.
5. For younger students: You may want to write student names on the containers, one with a hole and one without a hole for each student. Either a permanent marker or masking tape and crayon/pencil can be used.

Classroom activity PART ONE:

1. What does a plant need? Show students the potted plant. Ask students, "What does a plant need to grow?" Frequent responses include: sunlight, water, air, soil or dirt, and food. As a group discuss how each of these items helps the plant to grow.

2. Is soil always needed? Ask students, "Do plants always need soil to grow?" Ask them how they could find this out. Tell students they will be conducting an experiment to see whether plants can grow without soil.

3. Demonstrate set-up. Using the teacher demonstration materials, demonstrate how to make the growth chambers, described in 6a through 6g.

4. Fill the remaining demonstration container with soil. Plant three seeds equally apart from each other, and mist or water until the soil is moist at least one inch below the soil line. The soil will be moist enough if it holds together when you pinch some of it between your fingers. The hole in the bottom of the carton will help with drainage, but be cautious about over watering.

5. Send students to work in groups of 4-6 and distribute materials. If possible, have adult or older student volunteers assist as needed. If it has not been done already, have students write their names on a piece of masking tape, and put the tape on one of each student's cartons.

6. Students make the growth chambers.

a. Push a length of string through the hole in the top carton so that half of the string hangs below the bottom of the carton. Knot the string, to hold it in place, unless that has been done already. This string will serve as a wick.

b. Fill the top carton about 3/4 full with damp growing culture.

c. Put three seeds in the growing culture, at least 1 cm. apart. Students can use two fingers held together to measure between seeds.

d. Add half a cup of water to the bottom carton for cup-size cartons, and one cup of water for pint-size cartons.

e. Add two to three drops of nutrient solution to the water in the bottom carton. THIS SHOULD BE DONE ONLY BY AN ADULT. Students should avoid contact with the solution. If a student gets in contact with the solution, wash the area thoroughly with copious amounts of water.

f. Place the top carton, with the seeds and the growing culture into the bottom carton. Squeeze a little; it will fit! The string should reach from inside the top carton to the bottom of the bottom carton, so it can wick nutrient-rich water from the bottom carton into the growing culture in the top carton. To avoid spilling, THIS SHOULD BE DONE BY AN ADULT.

g. Cover the top carton with a wet paper towel.

7. Recording. After the growth chambers have been completed, distribute paper and crayons to the students. Ask them to each draw their No Soil growth chambers the way it looks today. Be sure their names are on their drawings. The day of the week and/or the date should be written by their names. Collect completed pictures and set them aside or post them near the growth chambers.

8. Predicting. When all the students have finished, lead them in a class discussion. Ask them to predict what will happen in their growth chambers. Remind the students that they do not have to agree with their classmates when they make their predictions.

Classroom Activity PART TWO:

1. Observing. Over the next seven days or so, remind the students to check their growth chambers every day for changes. They should also check to be sure the paper towel on top carton is wet. The seeds growing in the demonstration soil planter should also be checked and watered. The results of seeds planted in soil should be recorded.

2. Recording. When students notice a change in their growth chambers, ask them to draw (record) the changes they see taking place on a new piece of paper. The student's name and the day and/or date of the observed change should also be on these papers.

3. Communicating. Ask students to describe the changes they see in words. Remind students that the changes may not happen to everyone's growth chambers on the same day.

Students should observe sprouts emerging from the seeds. Depending upon the germination (growing) time required for the seeds you have selected, students should see results within a week.

Classroom activity PART THREE:

1. Comparing predictions with results. After most of the seeds have sprouted, ask students to remember their predictions. Were they surprised? Compare the results obtained in the growth chambers and in the soil.

2. Describing results. Bring out the students' original drawings. Put each student's drawings into chronological order, and staple them together, so that each student has a book describing what happened in their growth chambers over time. Invite students to describe their sequences of drawings.

3. How could we do it better? Ask, "What kinds of things about making no soil growth chambers were easy? What was difficult? How could we improve or change our experiment?"

Wrap-up

Tell students that they have been experimenting with hydroponics, which is a way of growing plants without using soil. The word itself means "water bridge." Ask if there something in the growth chambers that acts like a bridge between the water and the plant. (The string, or wick.) Challenge students to think of an occasion when it would be helpful to grow plants without using soil.

Scientists experiment with hydroponics on Earth to grow food and flowers, and in space. Some of the advantages of using hydroponics in space include:
* Takes up less space
* Uses less water (because the water is delivered to the plant more efficiently)
* Uses no soil (which is cumbersome to use in low gravity!)
* Reduces potential for bringing insects, weeds and other unplanned organisms into space
* Grows more quickly, since roots have more efficient access to nutrients
* Provides opportunities to obtain more information from astronauts' in-space experiments (by precisely controlling more variables)

People living in space for long periods of time might want to grow plants for food, for the oxygen they produce, and even for decoration. People could use hydroponics in space shuttles, space stations, or in space colonies.

More Activity Ideas

1. Make a bar graph of the growth of your plants. Try to start the measurements on a Monday, so the students will have five consecutive days to gather data. Consider how long it takes the seeds you have chosen to germinate (this is listed on the package) and plan accordingly.

a. When the plant appears, measure the same sprout each day for one week using strips of pre-cut green construction paper. If more than one sprout from the same growing chamber is going to be measured, use a differently colored strip for each sprout.

b. Bend the strip to show how long the sprout is. Cut the strip along the bend, so the strip will be the same height as the plant. Older students can measure the growth with a ruler. Younger students can be helped with a ruler, if appropriate.

c. Paste the strip onto paper to begin the graph. Put the day's date on or next to the strip. Measure and graph for one week. The strips offer a concrete representation of height that is helpful for younger students.

d. Lead the students in a discussion of what they observed. If students are not familiar with the concept of gravity, rent or borrow a video in which "weightlessness" or micro-gravity is shown from the perspective of astronauts in space. (See resources list at the end of this activity write-up.) Many children have seen this phenomenon on television. Explain that the force of gravity on Earth pulls everything down toward the center of the earth, but that the things we see everyday generally "stop" at ground level. Plants "fight" their way away from this pull by growing away from gravity, toward light from the sun. Their roots continue to grow down, usually. What would happen if there wasn't any gravity to pull plants "down," as in a space craft?

e. If students are familiar with the concept of gravity, ask them what effect gravity has on these plants. Explain that without gravity, the plants would be floating in space. Also, without gravity, the roots would "know" which way was "down" and the leaves and stem would not "know" which way was "up"! Ask students to predict whether the plants might grow taller or not grow as tall as the same kind of plants on Earth.

2. Take the plants out of the growing culture and wash the roots for closer observation.

3. Compare the life cycles of animals with that of plants-birth, growth and death. Compare the life cycles of perennial plants to annual ones. Contrast the life cycle of a flowering plant with that of a frog or a butterfly. For example: How does a plant begin life? (As a seed.) How does a frog begin life? (As an egg.) Then what happens? (The seed sprouts; the egg hatches and a tadpole comes out.) When does the sprout start to look like the parent plant? When does the tadpole begin to look like a frog? What happens to a plant when it dies? (It provides food for other plants and animals.) What happens to a frog when it dies? (The same thing.)

4. Try variations of this experiment, labeling each variation (with pictures if non-readers are involved). Be sure to make only one change per planting to more accurately track what causes each outcome.

Options include:
* Different kind of seeds (lettuce, radish or mung bean)
* No nutrients or a different kind/brand of nutrient
* Different kind of growth cultures (vermiculite, perlite mixture, potting soil)
* No growth culture (keep the seed in contact with the wicking string)
* No light (Seeds do not require sunlight to germinate, but will require sunlight after sprouting.)

Keep records and determine which changes (variables) work best.

Vocabulary
* growth culture - the medium or "stuff" into which the roots of a plant grow
* hydroponics - a system for growing plants without using soil
* leaf/leaves - the parts of a plant that are used to gather the sun's energy
* nutrients - food
* root - the part of the plant that absorbs moisture and nutrients. Roots also stabilize the plant, and keep it from bring blown or washed away.
* seed - something that grows into a plant
* seedling/sprout - a young plant grown from a seed
* stem - the part of a plant that grows out of the seed. Leaves grow out of the stem.

Skills:
* Students observe a plant and describe the parts of that plant.
* They predict what will happen when seeds are planted without soil.
* Students conduct an experiment. They each build a hydroponics system, plant seeds, and observe the outcome over time.
* They then compare the results of the hydroponics system seed plantings with the demonstration soil systems plants.
* Students draw conclusions about growing plants using hydroponics