There are many choices today of containers that can be used as terrariums. Anything large enough to hold plants, moisture and allow light to enter will work. Terrariums can be made from fish bowls, mason jars, bottles, vases, glass cookie jars or any other type of clear container that you can think of. A terrarium can have an open top or a lid, be short or tall, wide or narrow. Your choice of container however will dictate what types of plants you can successfully grow in your terrarium. Plants that thrive in high humidity can live in a covered terrarium whereas a cactus would quickly die. Carefully consider the type of plants you would like to grow first and then choose the appropriate container. A little research can go a long way to making a successful terrarium.
The drainage layer is simply a layer of rock, grow stone, sea glass, glass beads or gravel. It’s the first layer to go in the bottom of the terrarium and it allows excess water to drain through the soil and prevent the plant roots from rotting. This is a very important step in terrarium building. You will need enough material to create a ½” to 1” deep layer. If the container is short, go with a ½” layer. If it’s tall, use a 1” layer. For a 5” wide container, 1 cup = 1” deep. The key is to adjust the depth to accommodate the particular container you have chosen and to make sure you still have enough room for the other materials.
Horticultural charcoal is the second layer and goes on top of the drainage layer. It acts as a filter and keeps the terrarium fresh. You need a thin layer of charcoal and only enough to cover the drainage layer. Base the amount of charcoal you will need by purchasing half the amount used for the drainage layer. Make sure you rinse the horticultural charcoal with cold water before applying it to the terrarium or you will have the added step of trying to wash black dust off the inside walls of your terrarium. This dust clings to everything and is messy. Save yourself a lot of work and don’t forget to rinse.
Sphagnum moss comes loose or in dehydrated bricks and is available in many sizes. When soaked in water, sphagnum moss expands to many times its dehydrated size. Sphagnum moss is used as a barrier to prevent the soil from washing down into the drainage layer and only a thin layer is needed to accomplish this.
Soil that is used in a terrarium is not the same soil used in a potted houseplant. Terrariums stay moist and therefore the soil should be light and airy to allow for drainage and let the roots breathe. The soil should be double the depth of the drainage layer and deep enough to cover the roots of the plants being used. For a 5” wide container, 2 cups = 2” layer.
Sheet moss is an optional item used for decorative purposes. You will need enough sheet moss only to cover the exposed soil surface of the terrarium that remains after it is planted.
The amount of decorative items used is optional and based on personal taste. Certainly, rocks, pieces of wood or fairy garden items add interest to any terrarium and can give it that extra special look. Although a miniature landscape, terrarium soil can be terraced and the soil held back with rocks or wood and the different depths can add visual interest instead of just a flat landscape. Use your imagination in your creation and personalize it to your individual taste.
Choosing plants for the terrarium can sometimes seem a daunting task. Make sure to choose plants that are appropriate for a moist environment and ones that stay small. Of course, all plants grow and will need to be pruned regularly but slower growing smaller plants will save you a headache later on. How many plants do you need? It’s best not to overcrowd your terrarium. Keep in mind that the plants will grow and fill in the empty spaces so keep that in mind when deciding on the number of plants. For a terrarium of the 2-liter pop bottle width, no more than 3 are recommended.