To make a closed terrarium, choose a clear glass container with a lid, add sterile soilless potting mix with a little horticultural charcoal, plant small humidity-loving plants such as ferns, nerve plant and moss, mist lightly and close the lid. Place it in bright, indirect light and adjust the lid until only light condensation forms on the glass.
Key Takeaways
- Pick small, slow-growing, moisture-loving plants. Cacti and succulents are not suited to closed terrariums.
- Use sterile, soilless potting mix, not garden soil, and add a little horticultural charcoal.
- Water sparingly; you can always add water but it is hard to remove.
- Keep it out of direct sun, which can overheat the glass and cook the plants.
What is a closed terrarium and how does it work?
A closed terrarium is a sealed or lidded glass garden that recycles its own moisture. Water evaporates from the soil and leaves, condenses on the glass and drips back down, creating a small water cycle.
Once balanced, a closed terrarium needs very little care. Mississippi State University Extension notes that a balanced system may go weeks or months without added water (MSU Extension). Penn State Extension adds that with a tight lid, watering may be needed only every four to six months (Penn State Extension).
What do you need to make a closed terrarium?
- A clear glass container with a lid. Penn State Extension notes that colored glass blocks light. Cookie jars, apothecary jars, large canning jars and fishbowls with covers all work.
- Sterile, soilless potting mix. Garden soil compacts and can carry pests and disease.
- Horticultural charcoal. A handful or two, depending on container size.
- Small plants. Dwarf or slow-growing species that like humidity.
- Optional extras. Washed gravel, sheet moss, chopped indoor bark and non-porous decorations such as glass or glazed ceramic pieces.
- Tools. A long-handled spoon, tweezers or tongs, small snips, a cork on a skewer for tamping soil, and a mister.
You can find glass vessels in our terrariums and propagation collection and long-handled tools in our plant care tools.
Which plants are best for a closed terrarium?
Choose plants that enjoy moisture, stay small and share similar light needs. Mississippi State Extension's list of suitable closed-system plants includes (MSU Extension):
| Plant type | Examples |
|---|---|
| Ferns | Maidenhair fern, rabbit's foot fern, plumosa fern, artillery fern |
| Colorful foliage | Nerve plant (fittonia), Rex begonia, purple velvet plant |
| Trailing or creeping | Baby's tears, creeping fig, small ivy, pothos |
| Compact upright | Peperomia, pilea, dwarf palms, selaginella |
| Flowering | Miniature African violets, miniature phalaenopsis orchid |
Both Penn State and Mississippi State Extension advise against cacti and succulents in closed terrariums, since the humidity will cause them to rot. Moss and lichen are also good choices, according to Penn State.
Do you need a drainage layer in a terrarium?
Advice varies. Many guides, including Mississippi State Extension's, start with about an inch of washed gravel, followed by a thin layer of charcoal. Penn State Extension takes a different view, stating that rocks are no longer considered helpful for drainage and should be used only as a design element (Penn State Extension).
The common ground is this: a gravel layer will not fix overwatering. Careful watering is what keeps a terrarium healthy. If you like the look of layered stones, include them; if not, skip them and focus on the soil and plants.
How do you make a closed terrarium step by step?
- Prepare the plants. Water them in their nursery pots a few hours to a day before you start, as Mississippi State Extension suggests.
- Clean the container. Wash with hot, soapy water, rinse and let it dry. If you use a commercial glass cleaner, Penn State recommends leaving the lid off for a few days before planting so fumes can escape.
- Add an optional gravel layer. If using one, spread about an inch of clean gravel across the bottom.
- Add charcoal. Sprinkle a thin layer or mix a handful into your potting mix.
- Add potting mix. Add enough to cover the largest root ball, roughly 2 inches in many jars. The mix should be just damp, not wet.
- Plan the layout. Arrange plants while still in their pots. For a container viewed from all sides, put the tallest plant in the center. For one viewed from the front, put it at the back.
- Prepare each plant. Remove it from its pot, gently loosen the root ball and trim any yellowed leaves or stems that would touch the glass.
- Plant from smallest to largest. Penn State suggests starting with the smallest plants. Dig a hole with the spoon, place the plant and firm the soil with the cork tamper.
- Add finishing touches. Lay moss in patches, add chopped bark or decorative stones and place any non-porous ornaments. Keep it simple; small spaces crowd quickly.
- Mist lightly. Mist the inside of the glass to rinse off soil and mist the root zones. Stop before the soil darkens to a saturated color.
- Let leaves dry, then close the lid.
How do you balance moisture in a new terrarium?
New terrariums usually need a few days to settle. Mississippi State Extension recommends alternating the lid off and on in 24-hour cycles until condensation no longer builds up heavily on the glass (MSU Extension).
- Light fog on the glass that comes and goes during the day: balanced.
- Heavy droplets that never clear: too wet. Open the lid for a few hours or up to a day or two.
- No condensation, dry soil, drooping plants: too dry. Add a small amount of water.
Where should you put a closed terrarium?
Bright, indirect light is ideal. Direct sun through glass can quickly overheat the inside and burn plants. Mississippi State Extension suggests an east-facing spot with morning light, or a west-facing spot that avoids hot afternoon sun.
If your room is dim, a small LED grow light above the terrarium works well. See our grow lights collection and full spectrum LED grow lights explained.
How do you care for a closed terrarium?
- Air it out. Penn State suggests removing the lid for up to 15 minutes once a week, especially with very tight lids.
- Water only when needed. Add a little water when condensation stops, plants droop or the soil feels dry.
- Prune. Remove yellow leaves and any foliage touching the glass, which stays wet and invites disease.
- Rotate. Turn the container occasionally so plants grow evenly.
- Skip or limit fertilizer. Mississippi State says fertilizer is not needed. Penn State suggests a very dilute feed only after the first year, in spring.
What are common terrarium problems?
| Problem | Likely cause | Fix |
|---|---|---|
| Mold or fuzzy growth | Too wet, poor airflow, decaying leaves | Remove affected parts, open the lid for a day or two |
| Constant heavy condensation | Too much water | Leave the lid off until it clears |
| Plants leaning | Light from one side | Rotate the container |
| Scorched or yellow leaves | Direct sun overheating the glass | Move to bright, indirect light |
| Plants outgrowing the space | Normal growth | Prune or replace with smaller plants |
Penn State notes that diseases usually show up in the first few weeks, so watch closely early on. For more on balancing moisture with houseplants in general, see how to increase humidity for houseplants.
Shop the products in this guide
- Succulent Tool Kit, Mini Plant Care Set – Mini scissors, small shovels and a spray bottle for placing plants in a jar.
- Plant Mister Spray Bottle 17 oz, Fine Mist Sprayer – A fine mist for lightly moistening the terrarium before closing the lid.
- Mini USB Grow Light, 21 LED Desk Plant Lamp – A compact LED light you can aim at a terrarium in a dim room.
Frequently Asked Questions
How long does a closed terrarium last?
Mississippi State Extension suggests a typical display life of one to two years, after which plants can be pruned, rearranged or replaced.
Can I use succulents in a closed terrarium?
No. Closed terrariums are too humid for succulents and cacti. Use an open container for them instead.
Do closed terrariums need sunlight?
They need bright, indirect light or a grow light. Avoid direct sun, which overheats the glass.
How often do you water a closed terrarium?
Rarely. Water only when condensation stops forming or the soil feels dry, which may be weeks or months apart.