DIY Open Terrarium: Create Your Mini Glass Garden

The terrarium is a trendy alternative to traditional houseplants: beautiful and aesthetic, it allows you to host mini plants, whether jungle or desert-themed, in a glass jar. If you're new to terrarium-making, an open terrarium is likely the simplest and most rewarding choice. Follow our tips to create your own homemade terrarium: a creative activity, easier than you think, to recreate a miniature ecosystem at home!

An open terrarium… for which plants and where?

This is a classic terrarium but without an airtight lid or cork stopper. The open terrarium is therefore particularly suited to growing succulents (succulent plants and cacti), as it promotes good air circulation and limits ambient humidity. It is very easy to maintain. But it can also be considered for planting adapted mini foliage plants, if the container is deep enough, like a miniature jungle garden in your living room.

So it's your preference and the style of plants you love that will define your dream open terrarium! As you might guess, light levels will also determine plant choices. The brighter and warmer the room, the more suitable it will be for a mini cactus garden. Playing both a decorative and plant experimentation role, the open terrarium has its place in urban interiors where space is limited, as well as in larger living spaces, placed on a piece of furniture, inevitably sparking curiosity.

*The open terrarium meets the needs of succulent plants and cacti well*

Which plants to choose and how many to plan for?

Opt for mini plugs for small open terrariums, and miniature potted plants, as they will adapt better to the limited space. This will greatly facilitate planting and arranging the plants in the container. You can allow a few plants that will slightly overhang the pot, or trailing plants if you hang your terrarium.

Slow growth is an important criterion when selecting plants for an open terrarium. This helps maintain a harmonious composition without them becoming too large for the available space. Finally, always group plants from the same environment together, as they don't have the same needs, whether for substrate or watering maintenance.

Here are some examples of compact or dwarf plants, ideal for making an open terrarium:

Succulents and cacti for an arid decor

Prioritise dwarf succulents like Haworthia, Gasteria, Echeveria, Crassula ovata 'Minor', indoor Sedums such as Sedum rubrotinctum, Pachyphytum oviferum, a dwarf Aloe vera and/or small cacti like Mammillaria, Gymnocalycium, Rebutia or Echinopsis.

Foliage plants for a miniature jungle-effect terrarium

Mix compact ferns (Davallia fejeensis, Asplenium bulbiferum, Selaginella kraussiana), an Asparagus plumosus, very low and dense plants, with a moss-like appearance, such as Sagina subulata or Soleirolia soleirolii, and plants with colourful or unusual foliage (Fittonia, Pilea glauca, Peperomia 'Hope', Asparagus plumosus).
Note: miniature orchids (Masdevallia, Pleurothallis, etc.) require high ambient humidity, often difficult to maintain without a lid… As for carnivorous plants (Pinguicula and Drosera Capensis), they could be grown together, but they require very specific conditions, like in open ground (here, demineralised water and very high humidity), best left to experts.

*Top for dry terrarium: Houseleek and Crassula ovata 'Mina'; bottom for a humid terrarium: Fittonia, Asparagus plumosus and Pilea glauca*

Number of plants and spacing

For a large terrarium of 20 cm in diameter, allow about 3 to 5 small plants of 3-5 cm in diameter. This allows for a varied composition without overcrowding the space.

Leave approximately 2 to 3 cm between each plant to ensure good air circulation and avoid competition for root space. Maintain a border of at least 1 to 2 cm between the plants and the terrarium walls to prevent leaves from touching the glass, which could promote rot with jungle-type foliage plants.

Prepare your materials

The terrarium requires a number of specific elements. Identify and purchase not only the plants but also the essential accessories:

Container: a transparent glass jar with a wide opening to allow good ventilation. This could be a fishbowl, a round vase with a wide opening, a sweet jar with the lid removed, a pretty upcycled jar, or even a glass and brass box, like a jewellery box. It must be perfectly clean and dry before starting.
Substrate: this will vary depending on the type of plants.
- for a succulent terrarium: a light mix, such as special cactus compost or a half compost, half sand blend.
- for a foliage plant terrarium: a special houseplant compost mixed with a handful of activated charcoal flakes to prevent bacterial growth and bad odours
Gravel, clay pebbles or pumice for the drainage layer.
Plants: succulent plants, cacti for a dry open terrarium, or small foliage plants that tolerate a dry environment (see above).
Decorative elements (optional): stones, moss, shells, pieces of driftwood, etc.
Tools: long tweezers for handling plants or objects, or for levelling the substrate, a small trowel (optional), gloves for cacti, a spray bottle for watering.

*A side opening will always be practical. The glass container plays an important role in the visual appeal of a terrarium: choose it carefully* !

Assemble your terrarium in 5 steps

1. Drain the bottom of the jar

First, place the drainage material at the bottom of the container, about 4 to 5 cm deep. This will allow excess water to drain and prevent root rot. This is essential for both "dry" and "humid" terrariums.

2. Add the substrate

For succulents: pour a 5 to 10 cm layer of light substrate (see above) over the activated charcoal. Lightly tamp down the substrate to create a stable surface. Optionally add a thin layer of activated charcoal over the gravel.
For foliage plants: use the special houseplant compost mixed with a handful of activated charcoal flakes. This helps keep the substrate healthy and prevents bad odours. Add a layer of 5 to 10 cm depending on the depth of the jar.

3. Plant

Dig small holes in the substrate with the mini trowel and gently place your plants in them. Remember to leave enough space between each plant to allow good air circulation.

Start by planting the largest plants or those with the most developed root systems. This helps structure the space and ensures the roots have enough room to spread.

Next, add medium-sized plants, arranging them around the larger ones. Fill the gaps with small plants, ensuring a visually balanced composition.

If you're using trailing plants, like Senecio (syn. Curio) rowleyanus or Ceropegia woodii, place them near the edges of the container so they can elegantly spill over.

Gently firm the substrate around the roots to stabilise them.

For cacti, add some gravel, shells, or pumice for decoration and to prevent the collar from rotting. For a more humid environment, use your long tweezers to place moss (collected from the garden, which works perfectly well!).