What it shows
A plastic tunnel holds warmth and moisture and protects plants from wind and rain. Comparing a covered bed with an open bed shows how polyhouses extend the growing season.
The science
Clear plastic lets sunlight in, and the warm air inside cannot escape easily, so the tunnel stays warmer and more humid than outside. This helps seeds sprout and plants grow in cool weather. In hot weather the same cover can overheat the plants, so ventilation is needed.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Two small garden beds or trays of soil
- Bent wire or cane hoops
- Clear plastic sheet
- Two thermometers and a hygrometer (or humidity app)
- Seeds such as tomato or coriander
- A ruler and a notebook
Safety
For this project: An adult must bend wire hoops and cut plastic. Open the tunnel on hot afternoons so seedlings do not overheat, and wash hands after handling soil.
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.
Sow equal numbers of seeds in two identical beds.
Push the hoops into the soil over one bed and cover with plastic, leaving the ends open.
Place a thermometer in each bed at plant height and shade them from direct sun.
Record the temperature and humidity inside and outside at noon each day.
Water both beds with the same amount each day.
Measure the seedling height and leaf number every three days.
Compare germination time in the two beds.
Plot temperature and height for both beds.
What you should see
The covered bed is warmer and more humid, and seedlings sprout and grow faster until it gets too hot. The graphs show both the gain and the need for ventilation.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is a polyhouse warm?
Plastic traps heat from sunlight.
2What problem can overheating cause?
It can scorch plants.
3Why ventilate?
To control temperature and humidity.
4Which farmers use polyhouses?
Growers of flowers, vegetables and nursery plants.
Take it further
Add a shade net over the tunnel and test whether it keeps the temperature in the best range.
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.
Free ebooks for this project
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