Plant experiments for kids

How does a bean sprout without soil?

You need: a clear zip-top bag, a paper towel, 2-3 dry beans (lima or kidney beans), water, tape

1. Fold a paper towel in half and put it in the bag.
2. Wet it so it is damp but not soaking (water should not drip).
3. Place 2-3 beans on the towel, 2-3 cm apart.
4. Seal the bag and tape it to a window that gets light.
5. Look at the beans every day. When the towel dries out, add a few drops of water. Write down or draw what has changed.

What happens: In 2-5 days the bean swells, its skin splits and a white root appears. Then a green shoot appears and grows upward. You can see it all through the bag.

Why: A seed holds a store of food and a tiny baby plant. When the seed gets water, it swells and the baby plant wakes up. The root grows first, to look for water, and then the shoot. As long as there is food stored in the bean itself, it does not need soil to get started. Later the plant needs soil and light.

Safety: Raw beans must not be eaten, so keep them away from little ones who put everything in their mouths. If mold appears on the towel, throw the bag away without opening it near your face.

Try next: Put one bean in the same kind of bag but with a dry towel. What happens?

A green garden on cotton: light or dark?

You need: garden cress seeds, cotton balls, two saucers, water, a cardboard box or a large jar

1. Put a layer of cotton balls 1-2 cm thick on each saucer and soak the cotton well with water.
2. Sprinkle cress seeds thickly over both cotton gardens.
3. Put one saucer on the windowsill. Cover the other with the box so it is dark.
4. Add water every day to keep the cotton damp.
5. After 5-7 days, compare both gardens: height and color.

What happens: In the light, thick green grass grows. In the dark, the sprouts are longer and thinner, but pale yellow, almost white. If you used untreated seeds sold for sprouting or microgreens, the cress from the windowsill can be eaten in sandwiches.

Why: A plant gets its green color from chlorophyll, which forms in light. In the dark, the plant uses up the food stored in the seed to stretch up fast and find light, but it does not turn green. These pale sprouts are weak, because without light the plant cannot make its own food.

Safety: Wash hands after handling the damp cotton. Use untreated seeds sold for sprouting or microgreens. Eat the cress only if the cotton stayed clean, with no mold.

Try next: Put a saucer in a box with a hole in one side so the light comes from only one direction. Which way will the grass lean?

How does celery drink colored water?

You need: 2 celery stalks with leaves, a glass of water, food coloring (blue or red), a knife (for the adult)

1. Fill the glass halfway with water and add 15-20 drops of food coloring. Stir so the water is a deep color.
2. An adult cuts 1-2 cm off the bottom of the celery stalks to make a fresh cut.
3. Put the stalks, cut end down, in the colored water.
4. Leave the glass for 3-4 hours, or better yet overnight, in a bright, warm spot.
5. Look at the leaves and the stalk. An adult can cut the stalk crosswise and show the colored dots.

What happens: The veins in the leaves and the lines along the stalk turn the color of the water. On the crosswise cut you can see colored dots: these are tiny tubes inside the stalk.

Why: A stalk has thin tubes (xylem) that carry water up from the roots to the leaves. Water moves up because water evaporates from the leaves and pulls more water up the stalk behind it. The narrow tubes help, because water sticks to their walls. The coloring travels with the water, so it shows up wherever the water has gone.

Safety: Only an adult uses the knife. Food coloring can stain hands and clothes. It is best not to eat the dyed celery.

Try next: Have an adult cut a stalk lengthwise, then put the halves in glasses of different colors. Which leaves change color faster?

How does a root know which way is down?

You need: a sprouted bean in a bag (with a root 1-2 cm long), a clear zip-top bag and a damp paper towel, tape, a marker

1. Sprout a bean in a bag with a damp paper towel until the root is 1-2 cm long (about 3-4 days).
2. Tape the bag to a window or wall, and hold the bean in place with a folded damp towel so it does not slide down. With the marker, draw an arrow showing which way the root is growing now.
3. Carefully turn the bag so the root points sideways or up.
4. After a day or two, check which way the root has grown. Draw another arrow.
5. Keep the bag damp.

What happens: The new tip of the root bends and grows down again. The old part stays pointing the same way, and you can see a bend where you turned the bag.

Why: A plant senses which way Earth’s gravity pulls; this is called gravitropism. Cells in the tip of the root contain tiny heavy grains that settle to the bottom and show which way is down. Because of this, the cells on the upper side grow faster, and the root bends toward the ground.

Safety: If mold appears, throw the bag away without breathing it in. Wash your hands.

Try next: Turn the bag to another side again. How many times will the root change direction?

A plant finds the light in a maze box

You need: a shoebox with a lid, 2 cardboard dividers, a pot with a sprouted bean or pea, water, tape, scissors

1. An adult cuts a round hole 3-4 cm wide in one short side of the box (near the top).
2. Inside, tape two cardboard dividers to the bottom: one a third of the way along and one two-thirds of the way along. Leave a gap at the left end of one and at the right end of the other, so the plant has a zigzag path.
3. Put the pot with the sprout at the end farthest from the hole. Close the lid and tape over any gaps so light comes in only through the hole.
4. Set the box near a window with the hole facing the light.
5. Every 3-4 days, open the box and water the plant (so the soil stays damp). Take photos of how it grows.
6. For comparison, put the same kind of pot right on the windowsill and water it the same way.

What happens: After 1-2 weeks the sprout grows around the dividers toward the hole and leans toward the light. The plant on the windowsill grows straight up.

Why: Plants grow toward light; this is called phototropism. The tip of a sprout has a hormone called auxin, and more of it collects on the shaded side. The cells on that side stretch more, and the stem bends toward the light. This way the plant reaches more light, which it needs to make its food.

Safety: An adult handles the scissors. Do not leave the box unattended near a heater.

Try next: Move the hole or add more dividers. Will the plant find its way?