🪴 Do crowded seeds grow shorter?

My hypothesis

If I change how many beans share one cup, then how tall the tallest plant in the cup is on day 14 will ______, because ______.

🔊 You fill in the blanks. Think about what each plant needs from the soil and the light, and what happens when six of them share a cup. A guess is a good because: the test finds out.

Change, measure, keep the same

Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 3 levels 3 times.

What you need

• 🫘 Dried beans from the grocery bag (pinto, lima or kidney): 30, all the same kind
• 🥤 Paper cups with a hole poked in the bottom: 9, all the same size
• 🪴 Potting soil
• 🍽️ A baking tray or big plate: 1, to stand the cups on
• 🚰 Water from the tap
• 🥛 A measuring cup
• 🩹 Masking tape, to mark lines
• 🖍️ Crayons or markers
• 📏 A ruler

Steps

1. Soak 30 beans in a cup of water overnight.🔊
2. Fill nine cups with the same amount of potting soil, to 2 cm below the rim, and stand them on a tray.🔊
3. Label three cups 1 bean, three cups 3 beans and three cups 6 beans.🔊
4. Push the right number of beans a finger deep into each cup, spread as far apart as you can.🔊
5. Water each cup with a quarter cup of tap water, and set them all on the same bright windowsill.🔊
6. Every other day, give each cup the same quarter cup of water, however many beans it holds.🔊
7. On day 14, measure the tallest plant in each cup, from the soil to its highest leaf tip.🔊
8. Write each height in your table, in centimetres.🔊
9. Look at the stems and leaves, and write down which cups have thin, pale or small plants.🔊
10. Find the mean height for each number of beans and draw a bar graph.🔊
11. Wash your hands after touching the soil.🔊

Every step is one you can do yourself, with a grown-up nearby. Write each number down straight away, in the table below, so nothing is lost.

Your results table

From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a bar graph, one bar for each thing you tried.

Why it works

🔊 Plants in the same cup share one lot of soil, water and light, so each one gets a smaller share. Crowded plants may stretch tall in a race for light, but their stems are usually thinner and their leaves smaller. A single bean has the whole cup to itself.

Going further (7th and up): Change a second thing: use a bigger cup for each number of beans, and graph the height against the amount of soil for each plant.

Board layout

This project at your grade

Every grade this project fits works out a mean. See every project for 4th grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed how many beans share one cup and measured how tall the tallest plant in the cup is on day 14, in cm.
• What did you keep the same, and why does that matter? I kept the same size of cup, with the same amount of soil and the same kind of bean, soaked overnight the same, so the only difference was how many beans share one cup.
• How many times did you test it? 3 times at each of my 3 levels.
• If you did it again, what would you change or test next? I'd use a bigger cup for each number of beans, and graph the height against the amount of soil for each plant.

Make it yours

Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.

Try next

• 🌱 Do beans grow best in soil, sand or cotton?2nd–6th grade · 14 days of testing · about $3🌦️ Growing and weather · 🌱 Outside and plants
• 🌑 Does a bean grow taller in the dark?2nd–6th grade · 10 days of testing · about $2🌦️ Growing and weather · 🌱 Outside and plants