How to Make a Terrarium: Gardens Under Glass

What Are Terrariums?

Originally popularized during the Victorian era, terrariums have made a big comeback. A terrarium is a miniature ecosystem made of soil, rocks, and plants arranged in a closed glass jar or container. They are most suitable for ferns and moisture-loving tropical plants. A closed terrarium creates its own atmosphere and needs little from the outside except light. Think of a terrarium as a mini greenhouse!

In addition to being low-maintenance, a terrarium adds a pleasing houseplant container to your home that’s green all year long. 

Who Invented Terrariums?

A London physician accidentally invented the first terrarium in the early 1800s. Dr. Nathaniel Ward placed a cocoon in a covered jar so that he could observe the emergence of a sphinx moth. In time, several plants sprang up from the soil at the bottom of the jar, including a thriving fern. This surprised Ward because he had unsuccessfully tried to grow ferns in his yard and blamed the failure on polluted air from city smokestacks.

After his discovery, Ward constructed several fern containers, later to be called Wardian cases. These early terrariums quickly became popular, especially with the affluent, who had large, ornate cases made to display houseplants, miniature gardens, and woodland scenes.

How Do Terrariums Work?

A terrarium is a great way to observe how an ecosystem works! Moisture that condenses on the glass runs down to remoisten the soil. Then the plants draw moisture from the soil and evaporate it through their leaves, in a process known as transpiration. Water droplets form and drip down the sides of the container, returning to the soil. This process mimics nature’s rain cycle, and sustains plant life. The glass protects the plants from insects and diseases as well as from the dry air associated with many homes.

There are two types of terrariums:

1. The traditional “closed” terrarium is completely covered with a pane of glass. This is great for creating a humid environment. Excellent for ferns. 
2. However, you can also create an “open” terrarium, which is really more of a dry environment for succulents, cacti, and other desert plants that need very little water (but a lot of sunlight) and good air circulation. 

The Glass Container

Use almost any clear glass container, such as an aquarium or big fish bowl, to construct a terrarium. Even a cookie jar, a giant brandy snifter, mason jar, light bulb, or wide-mouthed bottle will work! If you are using an old aquarium, test it for leaks first; they can be fixed with silicone sealant to make the corners watertight.

Of course, you can certainly purchase specially designed closed glass terrariums online, as well as display cloches more reminiscent of the old Victorian style.

Just a hint: Planting is easier if you have chosen a wide-mouthed container! Otherwise, you may need to use long forceps to do your planting.

How to Make a Terrarium in 5 Steps

Supplies

• A clear container of your choice
• Pebbles, small river stones, or expanded clay balls used in hydroponics 
• Charcoal (activated charcoal, horticultural charcoal, or lump charcoal will all work as long as the product does not contain any additives)
• Potting soil (choose a well-draining soil to prevent it from getting compacted and waterlogged)
• Decor (wood, rocks, or other decorations)
• Plants (more on this later!)
• Planting tools: a spoon, long-handled tweezers, or even chopsticks can come in handy when planting in thin-mouthed containers

Instructions

1. Start by covering the bottom of the container with a 1-inch layer of pebbles or crushed stone. This drainage layer is used to keep the soil from becoming waterlogged and swampy.
2. Add chunks of charcoal to the stone or cover it with a 1/8-inch-deep layer of crushed charcoal to cover the pebbles. This helps with filtration and any odors.
3. Next, add 2 to 4 inches of sterilized potting soil on top of the charcoal, depending on the size of your container and the size of the plants. 
4. Now, you get to be creative and design your miniature landscape. If your container is large enough, the soil can be molded into hills and valleys to add interest; add rocks and small logs for a natural-looking setting. You could even add lakes, paths, statues, and driftwood.
5. Finally, it’s time to plant. Look for dwarf or low-growing plants that all have the same requirements for light, humidity, water, and temperature. Combine different sizes, shapes, colors, and leaf textures to make things interesting. Select plants that don’t mind wet foliage, such as moss, ferns, or prayer plants. Plant a woodland scene, use flowering alpines, get carnivorous, or go totally tropical.     

Once the terrarium is planted, cover its top with a pane of glass. If the sides fog up from excess humidity, leave the top open a crack so that some of the moisture evaporates from the container. A sealed terrarium will go for months, even years, without needing water. Place your terrarium out of direct sunlight to avoid overheating; fluorescent lighting is ideal. 

You will want to display your terrarium where it is sure to be noticed because it may just give the room—as well as your plants—a little atmosphere!

What Are the Best Terrarium Plants?

Most houseplants are tropical and make ideal residents for a terrarium. Miniature ferns, peperomias, African violets, and some orchids are all good candidates. Many woodland plants and mosses are also right at home under glass.

The two most important factors to consider when choosing plants for terrariums are their mature size and their ability to tolerate moisture. Plants that stay small and have a high tolerance for soil moisture and humidity will do best in sealed terrariums. Some plants that grow especially well in terrariums are:

• Ajuga
• Aluminum plant
• Artillery plant (Pilea)
• Baby’s tears
• Bird’s nest sansevieria (for open terrariums only)
• Bloodleaf (Iresine herbstii)
• Bromeliads (young plants only)
• Button fern
• Carnivorous plants: Venus fly traps, sundews, butterworts, cobra lilies, and tropical pitcher plants are all carnivorous plants that like humidity. (However, most non-tropical species need to experience a period of colder weather to thrive.)
• Chinese evergreen (young plants only)
• Creeping fig
• Earth star (Cryptanthus)
• Flame violet (Episcia dianthiflora)
• Mosses
• Oxalis
• Pellionia
• Peperomia
• Polka-dot plant (Hypoestes)
• Rabbit’s foot fern
• Small-leaf ivies
• Spike moss (Selaginella)
• Strawberry begonia
• Swedish ivy
• Variegated aloe (for open terrariums only)

Most nurseries offer a wide variety of “terrarium plants,” though these are more often than not just young plants that will eventually grow too large for your container. In general, look for plants that like a tropical climate and that grow in a creeping, vining, or clumping manner. 

Since cacti and succulents can’t tolerate humid conditions, they are not good candidates for a closed terrarium. Save them for an open dish garden, which can be created in the same fashion as a closed terrarium—just be sure to use a succulent soil mix for good drainage!

Taking Care of Your Terrarium

Once established, your terrarium will be very low maintenance. 

• Don’t plant too closely; allow some room for growth. Your terrarium won’t look instantly lush; plants need time to adjust and settle in.
• Water after planting; soil should be damp but not soaked.
• Place your terrarium where it will get bright light but not in direct sun, which will cook your plants. Artificial light is excellent.
• Leave the terrarium open for a few days while the plant leaves dry off, then put on the cover and keep a close eye on the plants.
• Excessive condensation, moldy plants, and limp yellow leaves are signs of overwatering. Open the cover and let your terrarium dry out a bit if that occurs.
• No condensation and plants with wilted leaves are signs of underwatering. Check the soil and water lightly if it seems dry.
• Leggy growth is a sign that your terrarium is not getting enough light.
• It’s normal to see small insects crawling around in your terrarium after a while. Usually, these are springtails, which are beneficial insects that help to break down dead plant material. They’re your terrarium’s clean-up crew!

Sit back and imagine yourself strolling through your mini-landscape, enjoying the greenery and humid air. Spring will be here before you know it!

→ Growing plants in the home? See our article on how to care for your houseplants.