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Biology > The
Water Cycle
Terrariums are wonderful projects: they're easy to plant, easy to care for
and they look wonderful. They also recycle their moisture, so they rarely
need to be watered, requiring almost no attention. Often, a closed terrarium
can be left for a month or more between watering.
Discussing the water cycle is a great introduction for this project. What
are clouds? What are they made of? What is rain? What does the sky look
like when it rains? Why does it rain? Where does the rain go after it falls?
What happens to puddles after it rains? These questions will start a discussion
about evaporation, condensation, and precipitation. Discuss each of these
things as you put your terrarium together. (You may want to check out the
animated
diagram of the water cycle from the US
Environmental Protection Agency.)
Any clear container can be made into a terrarium; just make sure that your
container is watertight. Choose something large enough to accommodate the
plants, and has a cover, lid, or door to keep the moisture from escaping.
Jars, bottles, and aquariums are commonly used and each works great. Whatever
the container, you can now easily bring nature into the classroom.
Many plants do well in terrariums, and it is best to choose the ones that
will fit the size of the container. Slower growing plants require less trimming,
and are less likely to take over. If you are willing to pay more attention
to them, you can experiment with more aggressive plants. They require more
frequent trimming, but will allow you to have more variety in your terrarium.
Some plants suitable for terrariums are:
Pilea (Aluminum Plant )
Fittonia ( Nerve Plant )
Ardisia
Podocarpus ( Buddhist Pine )
Aeschynanthus ( Lipstick Plant )
Baby Tears ( Very aggressive grower! )
Very small ferns
Miniature African Violets
Coffee Plant
Creeping Charlie
Boxus (Boxwood)
Wandering Jew (Aggressive Grower)
Creeping Fig (Aggressive Grower)
Moss
Planting Instructions:
- Place a 1/2 inch layer of small gravel in bottom.
- You may choose to sprinkle activated charcoal on top of the gravel,
but this is optional. It will help to filter the water as it drains
through the layers.
- Test your potting soil before using it by squeezing a handful. If
it clumps easily, add some Perlite or Vermiculite to help with drainage.
These can usually be found in garden shops. Add a 2-inch layer of potting
soil, or possibly a little more depending on the size of your container
and the size of the plants you intend to use.
- Add your plants, again taking into account the size of the space you
have to work with inside the terrarium. Be careful not to overplant
- you need to leave plenty of room for your plants to grow. Push the
soil aside, place a plant in the depression, and gently replace the
soil around the roots of each plant. Water lightly.
Care:
Neglect It! Water lightly only when the soil is dry. You should only
need to water, at the most, every couple of weeks, depending on conditions.
Be very careful not to overwater! Place in a bright area, but not in direct
sunlight. You should have enough light to read by. When plant gets as
big as you want, pinch off the newest growth to encourage bushier growth.
Do not fertilize. As the nutrients found in the potting soil get used
up, the plant's growth will slow, helping to keep the plant from overgrowing
the terrarium. Over time the soil can be "refreshed" by scraping
off the top layer of soil, and adding some fresh potting soil. This will
add a small amount of nutrient, and will spruce up the look of your terrarium
as well.
Small rocks, moss and dried twigs make good decorations and add to the
look of a micro-world of plant life. A terrarium can also be an ideal
place to observe insects, but you will want to return them to the outside
world after a few hours so they can survive in their natural habitat.
When your terrariums are finished, discuss the following: We only watered
the soil in our terrariums once; how did the water get on the lid? Take
your lid off the terrarium and feel the soil. Why is the soil still wet?
Do you think that any water has evaporated from the soil? Why? If water
evaporated, where did the evaporated water go? Did it ever rain in your
terrarium? How do you know? Where did the rain come from? Is there anything
in your terrarium that reminds you of a cloud or cloud drops?"
You may want to make a connection between the water cycle in the terrarium
and in the real world with a discussion using the following: "If
the terrarium is a model of the real world, what do you see outside that
reminds you of the plant in our terrarium? reminds you of the soil in
our terrarium? reminds you of the small water droplets on the lid? The
soil in our terrarium stays moist, the ground outside never dries out
completely. Why? What keeps it moist? Water collects on the lid of the
terrarium, water also collects in the sky as clouds, where does the water
in the clouds come from?
Keep your terrarium after the lesson is over and enjoy it for many months
to come!
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