🌱 Do beans grow best in soil, sand or cotton?

My hypothesis

If I change what the bean's roots grow in, then how tall the plant is on day 14 will ______, because ______.

🔊 You fill in the blanks. Think about what roots need besides water, and what each of these things can hold. 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): 9, all the same kind
• 🥛 Clear plastic cups, all the same size: 9, the same size
• 🪴 Potting soil
• 🏖️ Sand (from a sandbox, or play sand)
• ☁️ Cotton balls: about 30
• 🚰 Water from the tap
• 🥄 Measuring spoons
• 🩹 Masking tape, to mark lines
• 🖍️ Crayons or markers
• 📏 A ruler

Steps

1. Soak nine beans in a cup of water overnight.🔊
2. Fill three clear cups with potting soil, three with sand and three with cotton balls.🔊
3. Label the cups soil, sand and cotton, three of each.🔊
4. Push a bean a finger deep into each cup, or into the middle of the cotton.🔊
5. Give every cup two tablespoons of water, and set them all on the same bright windowsill.🔊
6. Every day, give each cup the same two tablespoons of water.🔊
7. Look through the clear cups each day, and draw what the roots are doing.🔊
8. On day 14, stand a ruler beside each plant and measure its height in centimetres.🔊
9. Write each height in your table, and a 0 for a bean that never came up.🔊
10. Draw a bar graph of the plant heights for each kind of cup.🔊
11. Wash your hands after touching the soil and the sand.🔊

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

🔊 Roots need water, air and something to hold onto. A bean has its first meal packed inside, so it can sprout in almost anything damp. Soil usually holds water and gives the roots minerals to take in, sand lets water drain away and has few minerals, and cotton holds water but little else, so the plant in soil often does best as it gets bigger.

Going further (7th and up): Change a second thing: add a fourth cup of half sand and half soil, and draw a line of every cup's height each week.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 2nd grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed what the bean's roots grow in and measured how tall the plant is on day 14, in cm.
• What did you keep the same, and why does that matter? I kept the same kind of bean, soaked overnight and the same clear cups, filled to the same level the same, so the only difference was what the bean's roots grow in.
• 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 add a fourth cup of half sand and half soil, and draw a line of every cup's height each week.

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

• 🪣 Which soil lets water through fastest: sand, potting soil or garden soil?3rd–8th grade · 1 day of testing · about $1🌦️ Growing and weather · 🌱 Outside and plants
• 🌱 Does planting a seed deeper make it slower to come up?3rd–8th grade · 14 days of testing · about $1🌦️ Growing and weather · 🌱 Outside and plants