Deborah J. Benoit
Editor’s Note: Deborah J. Benoit is a UVM Extension Master Gardener from North Adams, Massachusetts and a member of the Bennington County Chapter.
A terrarium is a miniature garden in a transparent glass container with a lid. Their closed environment requires little care and only occasional maintenance.
The container can be a jar, glass bulb, or an unused aquarium. Whatever size container you choose, make sure it’s thoroughly cleaned.
Choose plants that are naturally small and slow-growing or that can be kept small by pruning. and overcrowding fellow plants. For best results, choose plants with similar light and humidity requirements.
Plants to consider include small ferns such as ginkgo biloba (Adiantum microphyllum) and button fern (Pellaea rotundifolia), palm-like small tree plants (Biophytum sensitivum), polka dot plants (Hypoestes phyllostachea), and miniature African violets (Saint paulia). And so on. Carnivorous plants such as Venus flytraps (Dionaea muscipula) and sundews (Drosera) will appreciate the humidity provided by a terrarium. Additionally, moss can be the star of a small terrarium or act as a ground cover for a larger terrarium.
To provide a good base for your plant to grow on, start with a 1-2 inch layer of coarse gravel or small stones. Use thicker layers for larger containers. Since there is nothing in the terrarium container, this layer provides the necessary drainage.
Then add a thin layer of activated charcoal. Charcoal prevents odor and bacterial growth. The top layer, in which the plants grow, consists of 2 to 3 inches of light potting soil containing perlite and/or vermiculite.
Plan your plant placement using plates or paper the size of the planting area in the container. Taller plants should be placed behind shorter ones. Allow enough space for the plant to grow, especially near the walls of the container.
Once you’re satisfied with the design, remove the plant from its pot, remove excess soil, and free the roots. Make a hole in the terrarium soil and spread the roots to match the shallow soil depth. Gently press the soil around the base of each plant.
Depending on the container, it may be difficult to put the plant in by hand. Using long-handled spoons, dowels, chopsticks, tongs, etc., place each plant into the soil and hold it firmly in place.
Water sparingly by spraying or adding a spoonful of water. The soil can be covered with sand, gravel, colored ornamental stones, or a living ground cover such as moss. Consider adding shells, miniature figures, or other decorative accents. Finally, secure the lid in place to create a closed environment that requires minimal maintenance.
Open the lid slightly if excess water has accumulated inside the glass. Conversely, if the seal isn’t tight, you may need to water the terrarium regularly. With a tight-fitting lid, you may not need to add water for months.
As the plant grows, it may need to be pruned and tended regularly to remove unhealthy or damaged growth and to maintain its shape and size.
Choose a terrarium location with bright light, but avoid placing it in direct sunlight as the glass magnifies the sun’s rays, overheating the environment inside the terrarium and damaging the plants.
If you want a cactus or succulent terrarium that prefers much lower humidity, you can do so by creating an open terrarium the same way. Omit the lid to allow air to circulate. Monitor and water as needed.
Terrariums, large or small, are a great way to enjoy a small private garden, even in the dead of winter.