As the sun heats up our oceans, lakes, and rivers, water vapor is created through the process of evaporation. This warm water vapor rises into our atmosphere where it meets cooler temperatures. During the condensation stage, water vapor cools and transforms into clouds. Clouds become saturated with liquid water molecules and, when they can hold no more water, they release it back down to earth as precipitation. Rain, hail, and snow collect in bodies of water, and the cycle begins again.
THE WATER CYCLE INSIDE A TERRARIUM
The water cycle inside a terrarium is not much different than the one outside. The three stages are transpiration, evaporation, and condensation. In a terrarium, the glass vessel takes the place of our atmosphere by holding the soil, water, and all living things inside. First, water is transported from the roots through the plant’s leaves and released into the air through their leaves in a process called “transpiration.” As the sun heats up the vessel, water is evaporated into the air. If you look closely you may even see a light mist or fog inside. As the air inside the terrarium becomes humid, or saturated with water vapor, it starts to condense and create liquid water on the glass. Eventually the water slides down and back into the soil. The water is recycled over and over so there is no need to continuously water a closed terrarium.
SHOW ME THE LAYERS
Terrarium vessels do not have drainage holes, so it’s up to you to create a proper drainage system for your living display. In closed terrariums these layers play a crucial role in the water cycle. In an open container, they ensure proper drainage and keep plant roots from sitting in water for too long. The layers are presented in the order they should be followed. Of course, there is always a little room for creative interpretation.
LAYER ONE: DRAINAGE
This layer is also called a false bottom or water reservoir. It prevents plant roots from sitting in water, which can lead to rotting. Water percolates down into this layer until it can evaporate.
Drainage Mediums
• pebbles
• sand
• gravel
LAYER TWO: SEPARATION
This layer is optional but effective! It prevents the soil layer from falling into the drainage layer. This can get messy and take away from the overall appearance. Dried sphagnum moss is a popular choice for this layer. Before placing dried sphagnum moss into any terrarium project, first soak the moss in water for 10 minutes and then squeeze and drain out the excess water and let the moss dry. My favorite medium to use for this layer is fiberglass mesh. Hardware stores sell this mesh in rolls and the tiny holes in the screen allow water to easily pass through but deter the soil from falling through to the bottom. (Turn to the next page to see how to prepare it.)
Separation Mediums
• dried sphagnum moss
• butcher paper
• fiberglass screen sheet (window or fly screen)
HOW TO CUT FIBERGLASS MESH
Place your container on the screen. Use a marker to trace around the container and cut the screen.
If you don’t want the screen to show as prominently through the glass, you can cut it slightly smaller than the size of the container.
LAYER THREE: FILTRATION
This layer is used to filter the water that will come down through the substrate layer. Horticultural charcoal will help keep mold from growing inside the terrarium. It will also keep the terrarium smelling fresh and do away with that mildew-like scent that can sometimes accompany damp areas.
Filtration Medium
• horticultural charcoal
LAYER FOUR: SUBSTRATE
This layer is for the soil. The type of soil medium depends on the type of plants used. Some tropical plants prefer more acidic soil than others. We’ll talk more about the most suitable soil for your plants in the foundation section (see here). This substrate layer should be similar in depth to your drainage layer. Soil can become very saturated with water before it begins to percolate to the bottom. If the water reservoir is too shallow it will flood, and the roots of your plants will stay wet. This can lead to root rot and unfortunately kill your plants.
Substrate Mediums
• potting soil
• succulents and cacti soil mix
• peat moss soil mix
• orchid soil mix
LAYER FIVE: PLANTS
After you have layered the foundation of the terrarium it’s time to add your plants. The types of plants you use depend on the type of vessel. Remove plants from their pots, clean away any excess soil from the roots, and place them directly in the soil. Then cover the roots with soil, and pat down firmly.
Closed Terrarium Plants
• ferns
• mosses
• tropical plants
Open Terrarium Plants
• tillandsias (air plants)
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