Which kitchen scrap helps a plant grow most?
- 🧼 Wash your hands after
- 🚫 Test food is not for eating
- 🧽 A bit messy
My hypothesis
If I change what is mixed into the soil, then how tall the tallest blade of grass is on day 21 will ______, because ______.
You fill in the blanks. Think about what plants take from soil besides water, and what each scrap is made of. A guess is a good because: the test finds out.
Change, measure, keep the same
CHANGE
what is mixed into the soil: Plain soil, Soil with coffee grounds, Soil with crushed eggshell
MEASURE
how tall the tallest blade of grass is on day 21, in cm
KEEP THE SAME
- the same amount of grass seed, a teaspoon in each cup
- the same potting soil and cups
- a quarter cup of water in every cup each time
- the same sunny windowsill
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
- Grass seed
- Paper cups with a hole poked in the bottom: 9, all the same
- Potting soil
- Used coffee grounds, dried: 3 tablespoons, dried
- Eggshells, rinsed and crushed: 3 tablespoons, crushed
- A big bowl: 2, for mixing
- A baking tray or big plate: 1, to stand the cups on
- A measuring cup
- Measuring spoons
- Water from the tap
- Masking tape, to mark lines
- Crayons or markers
- 📏 A ruler
Steps
- Rinse some eggshells, let them dry, and crush them into tiny bits.
- In one bowl, stir 3 cups of potting soil with 3 tablespoons of dried coffee grounds.
- In a second bowl, stir 3 cups of potting soil with 3 tablespoons of crushed eggshell.
- Fill three cups with plain soil, three with the coffee soil and three with the eggshell soil.
- Label the cups plain, coffee and eggshell, and stand them on a tray.
- Sprinkle a teaspoon of grass seed on top of each cup, and cover it with a thin layer of its own soil.
- Water each cup with a quarter cup of tap water, and set them all on the same sunny windowsill.
- Every other day, give each cup the same quarter cup of water.
- On day 21, measure the tallest blade of grass in each cup in centimetres.
- Write each height in your table, and note if the grass is pale, bright or dark green.
- Find the mean height for each soil and draw a bar graph.
- Wash your hands well after touching the soil, the coffee grounds and the eggshells.
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
Name ______________________ Fair day ____________
Question: Which kitchen scrap helps a plant grow most?
I changed: Soil I measured: how tall the tallest blade of grass is on day 21 (cm)
| Soil | Try 1 (cm) | Try 2 (cm) | Try 3 (cm) | Mean |
|---|---|---|---|---|
| Plain soil | ||||
| Soil with coffee grounds | ||||
| Soil with crushed eggshell |
MY GRAPH (a bar graph: soil along the bottom, cm up the side)
What I noticed: ______________________________________________
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.
Name ______________________ Fair day ____________
Question: Which kitchen scrap helps a plant grow most?
If I change what is mixed into the soil, then how tall the tallest blade of grass is on day 21 will ________________, because _____________________________________________
| I CHANGE | I MEASURE | I KEEP THE SAME |
|---|---|---|
| Soil: Plain soil, Soil with coffee grounds, Soil with crushed eggshell | how tall the tallest blade of grass is on day 21 (cm) |
|
What I think will happen, in my own words:
Name ______________________ Fair day ____________
Question: Which kitchen scrap helps a plant grow most?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Which kitchen scrap helps a plant grow most?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Which kitchen scrap helps a plant grow most?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Which kitchen scrap helps a plant grow most?
My hypothesis was ☐ right ☐ partly right ☐ not right.
I know because my numbers show:
What surprised me, or what might have gone wrong (7th and up):
Next time I would test:
Idea: Change a second thing: use one, two and four tablespoons of coffee grounds in each 3 cups of soil, and graph the height against the amount.
Why it works
Plants take water and minerals from soil, and they make their own food from light. Used coffee grounds hold a little nitrogen, which leafy growth needs, and eggshell is mostly calcium but breaks down very slowly. A little of either might help, though potting soil often has plenty already, and too much of a scrap can slow a plant down.
Going further (7th and up): Change a second thing: use one, two and four tablespoons of coffee grounds in each 3 cups of soil, and graph the height against the amount.
Board layout
- ❓ Question (10 × 8 in): Which kitchen scrap helps a plant grow most?
- 💭 Hypothesis (10 × 9 in): If I change what is mixed into the soil, then how tall the tallest blade of grass is on day 21 will ______, because ______.
- 🧺 Materials (10 × 12 in): 12 things: see your list.
- 🪜 Steps (22 × 9 in): 12 steps, three tries at each level.
- 📊 Results (22 × 16 in): Your table (Soil down the side, tries across) and your bar graph.
- ✅ Conclusion (10 × 14 in): My hypothesis was right / partly right / not right. I know because…
Materials to list: Grass seed; Paper cups with a hole poked in the bottom; Potting soil; Used coffee grounds, dried; Eggshells, rinsed and crushed; A big bowl; A baking tray or big plate; A measuring cup; Measuring spoons; Water from the tap; Masking tape, to mark lines; Crayons or markers.
Bring photos or drawings of your test. Nothing wet, hot, powered or alive on the table.
This project at your grade
| 4th–6th grade | Tries: three at each level. The table: units in the header and a mean column. The graph: a bar graph, or a line for a number that grows. The conclusion: right, partly or not, and the numbers that show it. |
|---|---|
| 7th grade and up | Tries: three or more at each level. The table: a mean for every level of both tests. The graph: a graph with two lines or two sets of bars. The conclusion: the numbers, what might have gone wrong, and a next question. Second variable: use one, two and four tablespoons of coffee grounds in each 3 cups of soil, and graph the height against the amount. |
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 what is mixed into the soil and measured how tall the tallest blade of grass is on day 21, in cm.
- What did you keep the same, and why does that matter? I kept the same amount of grass seed, a teaspoon in each cup and the same potting soil and cups the same, so the only difference was what is mixed into the soil.
- 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 one, two and four tablespoons of coffee grounds in each 3 cups of soil, and graph the height against the amount.
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
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