🧅 Do green onions regrow best in water or soil?

My hypothesis

If I change what the green onion is left in, then how tall the green onion is on day seven will ______, because ______.

🔊 You fill in the blanks. Think about what an onion's roots can take in, and what it has stored up in its white base. 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

• 🧅 Green onions with their roots still on: 9, from one bunch
• 🥛 Clear plastic cups, all the same size: 2, the same size
• 🍽️ Small plates or saucers, all the same: 1
• 🪴 Potting soil
• 🚰 Water from the tap
• 🔪 A sharp kitchen knife, for the grown-up
• 📏 A ruler

Steps

1. Grown-up: A grown-up cuts nine green onions so each piece is 5 cm long from the root end.🔊
2. Stand three pieces, roots down, in a clear cup of water that just covers the roots.🔊
3. Plant three pieces, roots down, in a clear cup of potting soil, and give it a splash of water.🔊
4. Lay the last three pieces on a plate, with no water and no soil.🔊
5. Put the cups and the plate side by side on the same bright windowsill.🔊
6. Every day, top up the water cup and give the soil cup the same splash of water.🔊
7. On day seven, measure from the water, soil or plate up to each piece's tallest green tip.🔊
8. Write each height in your table, in centimetres.🔊
9. Draw a bar graph of the height for each way of growing.🔊
10. Wash your hands after touching the soil, and never eat the test onions.🔊

One step is a grown-up's, marked above. 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

🔊 A green onion keeps a store of food in its white base, and its roots take in water. With water or damp soil the roots keep working, and new green leaves grow up from the middle of the cut stem. On a dry plate the onion has only its own store to use, so it usually stops growing sooner.

Going further (7th and up): Change a second thing: stand the pieces in water beside a bright window, on a dim shelf and in a dark cupboard, and graph their heights each day.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 1st 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 green onion is left in and measured how tall the green onion is on day seven, in cm.
• What did you keep the same, and why does that matter? I kept pieces cut to the same length from one bunch and the same bright windowsill the same, so the only difference was what the green onion is left 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 stand the pieces in water beside a bright window, on a dim shelf and in a dark cupboard, and graph their heights each day.

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 potatoes sprout faster in the light or dark?2nd–6th grade · 14 days of testing · free🌦️ Growing and weather · 🌱 Outside and plants
• 🌱 Do plants bend toward the window?1st–5th grade · 12 days of testing · free🌦️ Growing and weather · 🌱 Outside and plants