Terrariums are closed transparent glass or plastic containers used to create a mini-environment or ecosystem for plants. The principle behind a terrarium is simple. The water from the soil is taken up into the plant as it grows. The water is then released through the leaves via transpiration. This water condenses on the glass and runs back to the soil where it can be used again. Because this mini water cycle occurs inside the sealed terrarium, the plants can go for months without watering. It also creates a jungle-like atmosphere of high humidity, warm temperatures, and no drafts, which are perfect conditions for many of the tropical-native houseplants common in homes.
The history of terrariums is rooted in the Victorian age. As Europeans traveled the globe, they used Wardian cases (which are early types of terrariums) to protect plants during their journey by sea from faraway places back to Europe. Terrariums were equally useful in growing tropical plants in the home. They were used in parlors to house many of the delicate and exotic plants being brought to Europe and North America from tropical areas around the world. Despite the fact terrariums have been around for many years, it has been difficult to match the popularity they saw in the 1850s.
Constructing a terrarium is easy, inexpensive, and can be accomplished on a snowy afternoon. Suitable containers can be found in most homes. Their care is minimal since they can go for months without water under the proper conditions. In addition, a wide variety of plants can be grown that would normally fail miserably in the dry, drafty environment of the average home.
Start with a clean, dry container. Terrariums or glass cases can be purchased at many stores, but an old 10-gallon fish tank, a large glass jar, or a large glass bowl with a beveled glass lid can also work. Any closed or semi-closed transparent container has the potential to become a terrarium, so feel free to be creative.
Since terrariums don't have drainage holes, place a 2-inch layer of gravel, pebbles, or perlite on the bottom of the container to provide a space for excess water to collect. Next, add a one-fourth-inch layer of charcoal. The charcoal aids drainage and helps control soil odors. Finally, add one to four inches of light, well-drained potting soil. In larger terrariums, as you are adding the soil, create hills and valleys to add interest.
Choosing the Perfect Plants
The next step is selecting your plants. Plants with slow growth rates, tolerance to high humidity, and small leaves make good candidates for terrariums. Because the plants will be planted in the same soil mass, the most important consideration is that all the plants tolerate the same soil moisture and other growing conditions.
When designing a terrarium, a general rule of thumb is to choose an upright-growing plant, a trailing plant, and a plant of intermediate size. A list of potential species for your terrarium can be found below.
A terrarium is not the place for a common philodendron or spider plant. Instead, use this special environment to grow unique, exotic, or otherwise difficult-to-grow plants in average home conditions. This includes plants like net plant, creeping moss, and ferns. Flowering plants, such as miniature African violets, and carnivorous plants, such as pitcher plants and venus fly traps, make beautiful and fun additions to terrariums. The humid environment is good for any houseplant except cacti and succulents, which suffer in a humid environment.
Planting and Finishing Touches
To plant a terrarium, remove the plant from the pot, gently shake off excess soil and place it in the soil inside the terrarium. Often a large portion of the root ball will have to be loosened or removed to allow the plant to fit in the small space.
Rocks and stones make good additions to your miniature landscape. Small shells, marbles, small figures, toy dinosaurs, or other similar items can also be added for a touch of fun. The options are limited only by your imagination; just remember not to incorporate wood. Driftwood or similar wood products will break down quickly inside a terrarium and could introduce unwanted insects and fungi, which will thrive in a terrarium's humid environment.
To finish your terrarium, moisten the soil by misting heavily or using a rubber bulb sprinkler. Soil stuck to the glass from planting can be rinsed off by lightly running water down the glass. After watering, cover with the lid, a piece of beveled glass, or saran wrap.
You Can Also Keep Them in Their Own Containers
In taller or larger glass cases, plants can remain in their own containers. This is particularly helpful for growing different species with very different soil or water requirements in the same terrarium, such as orchids with ferns. Cloches and bell jars can also be used to grow species in their own containers but create the same environment as a terrarium.
Place the terrarium in medium to bright, indirect sunlight. An east or north window would be a good choice. Heat can build up quickly when light is too intense, so avoid locations that get direct sunlight.
Fertilizer should be avoided because it will encourage growth and earlier crowding of the plants. Additionally, many potting soils already contain a small amount of fertilizer to help plants get established.
If plants exibit symptoms of low fertility (yellowing leaves, interveinal chlorosis, weak growth) fertilize with a balanced all-purpose fertilizer with low numbers in the fertilizer analysis (like 10-10-10 or 4-4-4) mixed at quarter strength.
Check on the terrarium every few weeks and add water when the soil becomes dry. Water will only be needed for many closed terrariums every 3 to 6 months, although the frequency can vary greatly based on soil type, plant species, light levels, and other factors.
If excessive condensation builds up on the glass, uncover the terrarium until some of the condensation evaporates; then replace the cover.
Managing Excessive Growth
Over time plants will begin to outgrow their space. Prune back plants as needed to keep the plants looking good. When plants become too unruly or large, pull them out and replace them with something else. No plant can be a permanent addition to a terrarium as all of them will eventually outgrow the space. Have fun and use it as an opportunity to change things up and try new plants.
Upright / Tall Plants
- Sweet Flag (Acorus gramineus)
- Holly Fern (Cyrtomium falcatum)
- Dracaena (Dracaena sp.)
- Bird's Nest Fern (Asplenium nidus)
- Peacock Plant (Calathea sp.)
- Net Plant (Fittonia sp.)
- Flame Violet (Episcia sp.)
- Cloak Fern (Didymochlaena truncatula)
- Table Fern (Pteris cretica)
- Pitcher Plant (Sarracenia sp.)
- Tropical Pitcher Plant (Nepenthes sp.)
- Sundew (Drosera sp.)
- Prayer Plant (Maranta sp.)
- Peperomia (Peperomia sp.)
- Begonia (Begonia sp.)
- Maidenhair Fern (Adiatum raddianum)
- Rabbit's Foot Fern (Davallia canariensis)
- Mini African Violet (Saintpaulia sp.)
- Venus Fly Trap (Dionaea sp.)
- Air Plant (Tillandsia sp.)
Low / Trailing Plants
- Earth Star (Cryptanthus sp.)
- Creeping Moss (Saleginella sp.)
- Baby's Tears (Helxine soleirolii)
- Strawberry Vine (Saxifraga sarmentosa)
- Creeping Fig (Ficus pumila)
- Aluminum Plant (Pilea sp.)