Mini Greenhouse

Recreate the story of Jack and the Beanstalk in a cup! Create your own mini-environment and grow some alfalfa, while finding out what plants need to survive.

Australian Curriculum links

  • Science > Biological Sciences > Foundation > ACSSU002
  • Science > Biological Sciences > Year 1 > ACSSU017
  • Science > Biological Sciences > Year 4 > ACSSU072
  • Science > Biological Sciences > Year 6 > ACSSU094
  • Science > Chemical Sciences > Year 9 > ACSSU179

You'll need

  • 2 plastic cups
  • sticky tape or electrical tape
  • cotton wool
  • alfalfa (or rocket) seeds
  • water

Try this

  1. Line the bottom of one cup with cotton wool.
  2. Dampen the cotton wool by sprinkling water on it.
  3. Evenly spread 4 or 5 seeds on the top of the cotton wool.
  4. Put the other cup upside-down on top of the first one (see picture) to create an enclosed container.
  5. Using tape seal the place where the cups touch to make it airtight.
  6. Place the mini-greenhouse in a sunny spot.
  7. Observe it daily to see what happens to the seeds.

Further investigation

Make several terrariums but make slight changes to each of them. You could place one terrarium in a dark place (like a cupboard) instead of near sunlight. You could add salty water to a second terrarium. You could try to not add any water at all to a third terrarium. You can measure the seedlings with a ruler each day to see which conditions help a plant to grow the best.

What's happening?

Another name for a mini-greenhouse is terrarium. A terrarium is an indoor enclosure used to grow and observe plants conditions that are similar to those found in nature. Most seeds require nutrients, water, carbon dioxide and sunlight to sprout and grow. This process is called germination.
The energy and nutrients a plant needs for germination are stored in the seed. Once the seed uses all of its nutrients the plant makes its own nutrients through the process of photosynthesis. In photosynthesis a plant uses carbon dioxide, water and the energy from sunlight to make sugar (a nutrient) and oxygen. Photosynthesis can be expressed as an equation:

Carbon dioxide + Water ---› Sugar + Oxygen
6CO2 + 6H2O ---› C6H12O6 + 6O2

This terrarium acts as a self-watering system. The water sprinkled on the cotton wool evaporates and forms water vapour when the terrarium gets warmer. The water vapour rises, and when it reaches the top of the terrarium it cools and condenses. When enough condensed water vapour accumulates, a drop will form and trickle down onto the cotton wool.
When the cups were placed together, some air was trapped inside. The trapped air contains enough carbon dioxide for the seed to survive for about a month. Once the seed runs out of carbon dioxide, it will have to be planted in some soil in the Sun and outside of the terrarium. The plant’s leaves will then collect carbon dioxide from the air and its new roots will collect vitamins, minerals and water from the soil.

Real world links

The largest seed in the world (according to the Guinness Book of World Records) is the seed of the giant fan palm (Locoicea maldivica), known as the double coconut or coco de mer. The seeds have a mass of up to 20 kg! The female trees have to be 100 years old before they produce the seeds. The seed takes a year to germinate and another year before it grows its first leaf.