What it shows
Plants can grow with their roots in nutrient water instead of soil. A bottle hydroponic setup shows that roots need water, nutrients and air, not soil itself.
The science
Plants take in water and dissolved minerals through their roots, then use sunlight to make food. In hydroponics the minerals come directly in the water, and the roots get oxygen from the air gap above the liquid. Nothing in soil is needed except support and the nutrients.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A 2 litre plastic bottle cut in half
- A cotton wick or rope
- Mint stems or spinach seedlings
- Cocopeat, perlite or small stones to hold the plant
- Liquid organic nutrient (vermicompost tea, diluted) or a plant nutrient mix
- A marker and a ruler
Safety
For this project: An adult must cut the bottle. Wear gloves when handling nutrient solutions, wash hands after, and keep the bottle away from children and pets.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
An adult cuts the bottle and turns the top half upside down inside the lower half to make a neck funnel.
Thread a cotton wick through the neck, leaving 10 cm below to dip into the liquid.
Fill the top part with cocopeat or small stones to support the plant.
Fill the lower half with nutrient water until the wick is wet but the roots do not sit in a deep pool.
Plant the mint stem or seedling in the medium so its roots touch the wick.
Place the bottle in bright light but not harsh midday sun.
Top up the nutrient water each week and change it every two weeks.
Measure the height and count the leaves weekly.
What you should see
The plant grows new leaves and roots in the bottle, and the measurements show healthy growth without soil.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What does hydroponics mean?
Growing plants in water with nutrients.
2Why do the roots need air?
Roots respire and need oxygen.
3What does the plant get from the nutrient water?
Minerals such as nitrogen, phosphorus and potassium.
4Why is it useful in cities?
It saves space and can use less water.
Take it further
Grow the same plant in soil and compare height and leaf count after three weeks.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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