Terrarium

A terrarium is an enclosed system to grow plants in. They are easy to make and can help us understand parts of the water cycle. You could also use it as a seed germinator too.

Difficulty:

Time: 20 minutes

Adult supervision: yes

Dangers: cutting involved. Do this activity outside. Wear gardening gloves.

Materials

Large, clear plastic bottle (soft drink, water over 1L is best)

Scissors or craft knife

Seeds or small plants

Water

Gravel (optional)

Soil or potting mix

Gardening gloves

Sellotape

Method

Remove the label from the bottle. HINT: Eucalyptus oil is great for removing sticky adhesive left after label removal.
Carefully cut the bottle about halfway.
If you have gravel (or very small stones) place enough to cover the bottom of the bottle.
Put soil or potting mix into the bottle (about 1/3 of the bottle). If the potting mix or soil is quite dry, it may be best to mix it with water before putting into the bottle.
Sow your seed (check seed packet for depth) or add your plant. We made two (one with a bean seed and one with a parsley seedling).
If you haven't already, add water. Make sure you don't make the soil too wet as this may cause the seed to rot.
Place the top part of the plastic bottle over the rest of the bottle.
Before bringing inside, wipe the outside of the with a damp, soapy cloth to remove any dirt.
Seal with Sellotape.
Put your terrarium in sunny spot. How long did it take before you saw condensation? How long did it take for your seed to germinate?

Making a hole in the soil for our bean seed

We found a parsley seedling for our second terrarium

Tape the bottle around the join to seal it.

The Science

The Water Cycle or Hydrologic Cycle

Water is constantly being cycled through many stages of the water cycle. Our terrarium demonstrates a few of these processes.

There are 5 main processes:

Condensation: in this process, water changes from a vapour or gas to a liquid. As water vapour rises, it loses energy and changes state to a liquid (water) or sometimes, a solid (ice).
Precipitation: this is rain, sleet, snow or hail. When water vapour condenses in the atmosphere, it becomes too heavy and falls as rain.
Infiltration: Precipitation that reaches the Earth's surface soaks into the ground in a process called infiltration.
Runoff: Precipitation that doesn't infiltrate the ground flows off and is called runoff. It will drain into creeks, rivers and oceans. Some will evaporate.
Evapotranspiration: This is how water re-enters the atmosphere.

- Evaporation occurs when sun heats water molecules and they rise in the atmosphere as water vapour.

- Transpiration is water released from plants through their leaves.

Another process in the water cycle is sublimation. This is when ice turns directly into water vapour. This happens on mountains (glaciers) and on Antarctica.

In our terrarium...

The plants are carrying out transpiration.

Evaporation: water from the soil evaporates

Condensation: the water vapour condenses on the sides of the bottle.

Precipitation: when too much water forms it runs down the side of the bottle

Infiltration: the water soaks back into the soil).