Posted: January 14, 2026
A miniature world of plants, thriving in a container, viewable at close range, makes for a perfect way to brighten one’s spirits in the middle of winter. Terrariums are such created worlds.
Examples of terrariums. Photo by Susan Marquesen.
Making a terrarium can be a fulfilling activity, whether done individually or as a shared experience with children.
Terrariums came into being accidentally in 1833 when Nathaniel Ward decided to study insect behavior. He placed a cocoon in a closed container filled with plants and was impressed at how the plants, especially ferns, thrived. A friend took a number of these glass boxes, then called "Wardian cases", on a plant collecting expedition to Australia. Plants growing in the cases had a 95% survival rate compared to 5% of plants growing outside of the boxes. Ward wrote several papers on this discovery, and Wardian culture took off in 1842. By the late 1800’s Wardian cases were referred to as terrariums.
Decide which type of terrarium appeals to you, as well as the light conditions and temperature you can provide. You can create vignettes that evoke a woodland or desert. A woodland terrarium has a higher humidity level where ferns, Peperomia species, or baby’s tears (Soleirolia spp.) will thrive. A closed terrarium with a lid provides a self-watering and sustaining environment. Closed terrariums are described in this article.
Drought and heat-tolerant succulents like Aloe, Echeveria, and Sedum species are best suited for open terrariums. If planting succulents in an open terrarium, use a cactus mix that can be found at a local nursery or mix two parts of potting soil to one part coarse sand, perlite, or bonsai grit.
Another specialty type of terrarium replicates a wetland, having distinct areas for land and water species. These are called paludariums; they are a hybrid of a terrarium and aquarium. Plants selected to grow in a paludarium thrive in high humidity and wet soils and may grow submerged in water.
For a classic closed terrarium, you will need a clear container with a lid. Site your terrarium in bright light, but not direct sunlight. Choose from a variety of glass containers, ranging from old aquariums, vases, or mason jars. When choosing plants, consider size, scale, color, and height. Choose an anchor plant that will be the star of the composition. Smaller plants can be added to complement the tallest plant, right down to mosslike plants such as baby’s tears.
Begin by washing the container with hot, soapy water, rinsing thoroughly, and drying. The key to creating a healthy terrarium is to provide a clean, disease-free environment. It was once thought that gravel in a terrarium assisted with drainage. Gravel can be an aesthetic choice, but is not required. Gravel can be used on the bottom of the terrarium or as a top-dressing to the soil. Add enough soil to the bottom of the terrarium to support the root mass of the largest plant. Choose fresh potting mix to create a healthy environment for your plants. You can mound the soil a bit to create dimension within the space and provide a site for slightly larger plants. Mix a handful of activated charcoal into the soil. This helps in the absorption of minerals and the elimination of odors. Gently tap the soil before adding plants.
When adding plants to a closed terrarium, choose those that tolerate high humidity and have slower growth rates. Be sure to untangle roots before planting. If needed, a long pair of tweezers can be used to help place plants in their desired location. Pack the soil after all the plants have been added. Gently mist the plants and soil. Allow the foliage to dry, then close the terrarium. More details on creating a healthy ecosystem within your terrarium can be found at: https://extension.psu.edu/creating-a-closed-terrarium
Stones, lichen, driftwood, pinecones, and other natural objects look at home in a terrarium. Moss is a perfect element in a terrarium. Look for preserved mood moss or cushion moss. Both can add a gentle softness and dimension to your vignette. Whimsical accessories such as gnomes, toys, or items used in fairy gardens can be added. Look for inspiration in books or online images.
Once your terrarium is established, supplemental watering is rarely necessary. However, should your terrarium develop too much water on the inside of the glass container, remove the lid and siphon or sponge excess water. Watch your plants and remove any foliage that begins to show signs of disease. If a plant looks unhealthy overall, remove it to retain the integrity of your terrarium. Healthy plants are key to the longevity of the terrarium.
Longevity in the world of terrariums is exemplified by the oldest and longest living closed terrarium, which was planted by David Latimer in 1960. He sealed the glass container in 1972 and since then, it has remained almost completely untouched!
Celeste Biordi Janosko is a Penn State Master Gardener. This volunteer program supports the outreach mission of Penn State Extension and provides research-based information on best practices in sustainable horticulture and environmental stewardship. For more information, contact the Penn State Extension of Allegheny County at alleghenymg@psu.edu or 412-482-3476.
Published in the Pittsburgh Post-Gazette 2025/12/26.
