How to Create a Captivating Closed-System Terrarium

Terrariums are an exquisite addition to any living or working space, serving as stunning interior accents. These glassy enclosures draw viewers in, revealing the intricate beauty of the plants they hold. They offer a small-scale ecosystem—a mesmerizing glimpse into the natural world. Humans have an innate fondness for nature, and while our modern lifestyles may limit our time outdoors, terrariums provide a way to experience the unique flora that nature has to offer. Terrariums are not just decorative pieces; they are living sculptures that require minimal maintenance.

Types of Terrariums

Terrariums can be classified into two main types: open systems and closed systems. Open-system terrariums are housed in containers with wide openings, such as large glass bowls. These terrariums require more frequent watering and have lower humidity levels. Currently, a popular trend involves using succulent plants or cacti in open-system terrariums. These plants, native to arid regions, thrive in the drier environments provided by these terrariums. Both open-system and closed-system terrariums can support the plants listed at the end of this article.

Closed-system terrariums, on the other hand, are housed in closed or nearly closed containers. A jar with a narrow mouth or a lidded jar, like the one depicted in this article, works best for creating a closed-system terrarium. These containers create the ideal ecosystem for plants that require moisture and humidity. However, it is important to note that succulents and cacti do not fare well in closed-system terrariums as they are prone to rot in such environments.

Closed-system terrariums are surprisingly easy to maintain once the ecosystem is established. Therefore, this article focuses on the creation of a closed-system terrarium.

Terrarium illustrating the water cycle

Selecting a Display Site

Before you start purchasing plants and supplies, it is crucial to choose an ideal location to display your terrarium. You’ll want it to blend seamlessly with your interior style. Consider how it can be showcased, whether on a table or a plant stand.

It’s advisable to keep the terrarium in a dedicated space and avoid moving it to different locations frequently. Changes in light intensity and duration can negatively impact the health of the plants. Find a spot with bright, indirect light—preferably an eastern exposure with morning sun. A western exposure can also work, as long as you protect the terrarium from the heat of the afternoon.

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Avoid placing the terrarium too close to a window, as excessive solar energy can generate heat inside the container, potentially harming the plants.

Less is More

Terrarium supplies can be found at plant supply departments or online. In addition to the container itself, decorative accessories can enhance the overall design. These accessories can be made of ceramic, glass, metal, or plastic, as long as they are impervious to moisture. You can choose to make them a dominant part of the design or keep them subtle to maintain a natural look.

For instance, in this project, heat-treated bark is used. It is important to avoid using outdoor landscape bark, as it may harbor disease-causing pathogens that can harm the terrarium. By using heat-treated bark, you can introduce an element of texture and pattern to complement or substitute the use of moss. Consider using only one variegated, fancy-leaved plant alongside other green plants for an eye-catching effect.

Horticultural-grade charcoal, consisting of pure carbon chips measuring around one-fourth of an inch long, is utilized to provide water filtration. Aquarium charcoal can also be used, although it may be slightly more expensive. Clean, washed gravel and sterile potting mix should be used in combination with the charcoal.

Caring for and Displaying Your Terrarium

To maintain a healthy moisture balance within the terrarium, it is important to follow these steps:

  1. After completing the project, leave the container open for about 24 hours to allow excess water vapor to escape.
  2. Replace the lid for 24 hours.
  3. Remove the lid for another 24 hours to allow condensation to evaporate.
  4. Repeat the process of replacing the lid for 24 hours and removing it for another 24 hours until no moisture collects on the interior glass of the terrarium.
  5. At this point, the terrarium has reached an equilibrium and can go weeks, or even months, without requiring additional watering.

Terrariums are meant to experience slow growth, reducing the need for frequent pruning. Adequate air, moisture, and sunlight support photosynthesis, allowing the plants to thrive. Fertilizer is unnecessary in closed terrarium systems.

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Typically, terrariums have a display life of one to two years. As plants mature, they may outgrow the jar, requiring pruning or removal. This presents an opportunity to refresh the design by rearranging the existing plants or adding new ones. It’s a fun and relaxing activity that can be enjoyed any time of the year!

A completed terrarium

Project Materials*

Terrarium project materials

  • Container (2-gallon glass jar)
  • Plant selections (Neanthe bella palm, nerve plant, Boston fern ‘Fluffy Ruffles’)
  • Finely chopped, heat-treated bark
  • Gravel
  • Horticultural-grade charcoal
  • Potting mix
  • Moss (undyed sheet moss)
  • Decorative items (miniatures, shells)
  • Mist bottle and water
  • Scissors or snips
  • Newspaper or other paper

*Not all materials listed are necessary for every project. Plant supply departments often carry an array of terrarium supplies. Alternatively, you can find these materials online.

Step-by-Step Guide

  1. Water the plants in their original pots a few hours or the day before constructing the terrarium.
  2. Ensure the terrarium container is clean before use.
  3. Lay down a few layers of newspaper on your work surface for easy cleanup.
  4. Add 1 inch of gravel to the bottom of the container.
  5. Make a funnel using two or three layers of newspaper or other paper. Use the funnel to slowly add approximately ¼ inch of charcoal to the container.
  6. Add around 2 inches of soil mix to the container, creating a hole large enough to accommodate the root balls of the plants.
  7. Carefully remove the plants from their pots and loosen the soil at the top and bottom of the root balls.
  8. If multiple plants of the same variety are present in a pot, gently separate them by opening up the root ball with your fingers.
  9. Trim any leaves or stems that may touch the sides or lid of the container.
  10. Position the tallest plants in the center and place the remaining plants around them, leaving some space between each plant. Assess whether additional pruning is necessary.
  11. Add the plants to the container and tamp down the soil around the root balls.
  12. Using a mist bottle, lightly mist the interior sides of the glass jar. This not only provides water to the soil but also helps clean any charcoal dust or organic materials from the glass. Make sure the soil appears saturated but avoid over-saturating it. Extra water can be added if needed; however, it cannot be easily removed from the terrarium.
  13. Break up large pieces of moss and place them in patches on the soil surface. Add chopped bark to other patches. Finally, arrange decorative items as desired.
Further reading:  The Art of Nurturing Fiddle Leaf Fig Trees: Mastering the Use of Fertilizer

Choosing the Right Plants

Plants Suitable for Open-System Terrariums (Cacti and Succulents):

  • Aeonium
  • Aloe vera
  • Burro’s tail
  • Cactus
  • Crown of thorns
  • Devil’s backbone
  • Echeveria
  • Flaming Katy (Kalanchoe)
  • Hens and chicks
  • Jade plant
  • Panda plant
  • Pencil plant

Plants Suitable for Both Open- and Closed-System Terrariums:

  • African violets (including miniature African Violets)
  • Anthurium (miniature varieties)
  • Ardisia
  • Artillery fern
  • Baby’s tears
  • Bead plant
  • Creeping fig
  • Croton
  • Dieffenbachia
  • Dracaena
  • Dwarf schefflera
  • Fern
  • Flame violet
  • Gold dust Dracaena
  • Ivy
  • Lipstick plant
  • Maidenhair fern
  • Nerve plant
  • Norfolk Island pine
  • Orchid (such as miniature Phalaenopsis)
  • Palms
  • Peperomia
  • Philodendron
  • Pilea
  • Plumosa fern
  • Pothos
  • Purple velvet plant
  • Rabbit’s foot fern
  • Rex begonia
  • Selaginella
  • Spider plant
  • Strawberry begonia
  • Tillandsia
  • Venus flytrap
  • Zebra plant

Ensure that foliage or stems do not rest against the glass surface, as this can adversely affect the health of the leaves, plants, and the overall terrarium system. Moisture can get trapped between the leaf and the glass, creating an environment conducive to disease. Also, avoid plants touching one another to prevent the rapid spread of disease.

References

  • Carloftis, J. (2006). Beyond the windowsill. Franklin, TN: Cool Springs Press.
  • DelPrince, J. (2013). Interior plantscaping: Principles and practices. Clifton Park, NY: Delmar.
  • FTD Fresh. (2014). Twenty popular types of succulents. Retrieved from https://www.ftd.com/blog/share/types-of-succulents
  • Hessayon, D. (1998). The house plant expert. London: Transworld Book.
  • Martin, T. (2009). The new terrarium. New York, NY: Clarkson Potter.
  • Pleasant, B. (2005). The complete houseplant survival manual. North Adams, MA: Storey.

Please note that the information provided in this article is for educational purposes only. No endorsement of commercial products, trade names, or suppliers is implied, nor is any discrimination against other products or suppliers intended.

Publication 3253 (POD-08-21)
By James M. DelPrince, PhD, Associate Extension Professor, and Gary Bachman, PhD, Extension/Research Professor, Coastal Research and Extension Center.

To browse a selection of terrarium supplies, visit the Ames Farm Center.