A terrarium is a small garden inside a clear container, where you can arrange plants and watch how they grow. To make one that lasts, match the plants to the container, provide drainage and suitable light, and avoid keeping the soil constantly wet.
Before you begin, decide whether you want an open or closed terrarium. Open containers suit plants that prefer drier air, such as many succulents; closed containers create a humid environment for moisture-loving tropical plants. Most plants do best in one type or the other, so avoid mixing plants with very different needs. Choose a clear container and plants that will remain small enough for its space.
What You’ll Need
- A clear glass container: an open vessel or a container with a removable lid. It should be clean and large enough to place plants without crushing their leaves.
- Small plants suited to your chosen setup. For an open terrarium, consider compact succulents or other plants that tolerate dry air. For a closed terrarium, choose small tropical plants that prefer humidity, such as fittonia or certain small ferns.
- Potting mix appropriate for the plants. Use a freely draining mix for succulents; a general houseplant mix can suit many humidity-loving plants.
- Small stones or gravel, optional. They can hold a little excess water below the soil, but do not replace a drainage hole.
- Activated charcoal, optional. A thin layer is sometimes used to help limit stale odors, but it does not keep a terrarium clean or prevent overwatering.
- A small scoop, spoon, or folded piece of paper for placing soil.
- Long tweezers, chopsticks, or another narrow tool for positioning plants.
- A spray bottle or small watering can, plus a clean cloth for removing soil from the glass.
Step-by-Step
- Choose the terrarium type. Pick an open container for plants that need airflow and a relatively dry environment. Choose a closed container only for plants that tolerate high humidity. A closed terrarium is not suitable for most cacti and succulents, which are prone to problems in persistently damp conditions.
- Select a container and position. Make sure the glass is clear, stable, and easy to reach into. A wide opening makes planting and later pruning easier. Place it where the intended plants will receive bright, indirect light. Direct sun can heat the glass and damage plants, especially inside a closed vessel.
- Clean the container. Wash it with warm water and a little dish soap, rinse thoroughly, and let it dry. Remove any dust or residue so you can see the soil and monitor condensation later. Clean tools and remove dead leaves from the plants before planting.
- Prepare the plants. Check each plant for pests, damaged leaves, or signs of rot. Gently ease it from its nursery pot and loosen only enough soil to position its roots. If roots are tightly circling, tease them apart carefully rather than pulling on the stem. Do not combine plants simply because they look good together; their light, moisture, and temperature needs should be compatible.
- Add an optional base layer. If you like, place a shallow layer of small stones at the bottom, followed by a little activated charcoal. Keep these layers modest so there is room for soil and roots. Remember that a container without a drainage hole can still become waterlogged: water that passes the soil collects at the bottom rather than draining away.
- Add the potting mix. Use enough soil to support the roots and give the plants room to settle. Shape the surface into a low mound or gentle slope if you want a more natural appearance. Avoid pressing the mix into a dense, hard layer, which can restrict air around roots. Keep soil off the sides of the glass as much as possible.
- Position the plants. Make small planting holes with a spoon or your fingers. Set each plant in with its roots covered and its crown—the point where leaves meet the roots—above the soil. Leave a little space between plants for airflow and growth. Turn the container as you work to check how the arrangement looks from different sides.
- Settle the soil and tidy up. Gently press the soil around each plant so it stands upright, but do not compact it firmly. Use a soft brush, cloth, or narrow tool to remove soil from leaves and glass. Pick out fallen leaves, since decaying material can encourage mold, especially in a humid closed terrarium.
- Water sparingly. Add a small amount of water near the soil rather than soaking the foliage. For a closed terrarium, begin with just enough to make the soil lightly moist, not saturated. For an open terrarium, water according to the plants’ needs and let the mix dry as appropriate for that type. Because there is no drainage hole, it is easier to add water later than to remove excess.
- Observe and adjust. Keep the terrarium in bright, indirect light and check it over the following days. In a closed setup, light condensation on part of the glass can be normal. If the glass stays heavily fogged or water runs down the sides for much of the day, open the lid to let moisture escape. If there is no condensation and the soil looks dry, add a little water. Make changes gradually.
Common Mistakes
Mixing plants with different needs: A cactus and a humidity-loving fern may look appealing together, but one will be kept too wet or the other too dry. Group plants by their preferred moisture, light, and airflow instead of appearance alone.
Overwatering: A closed container recycles moisture, and a container without a drain cannot release excess water. Water in small amounts, inspect the soil, and do not follow a rigid schedule. If the soil is already damp, wait rather than adding more.
Putting the terrarium in direct sun: Glass can intensify heat around the plants. A bright windowsill may receive direct rays at some times of day even if it looks shaded at others. Choose a spot with bright, indirect light and move the vessel if its contents become hot or scorched.
Planting too densely: Crowded leaves trap moisture, touch the glass, and make pruning difficult. Start with fewer plants than seem necessary. Small plants can grow, and open space helps air circulate.
Assuming gravel provides drainage: A gravel layer does not give water a way out of a sealed vessel. If water collects below the soil, the roots may still sit in a humid, stagnant environment. Use little water and check the bottom of the container.
Leaving dead material in place: Fallen leaves and damaged roots can decay and contribute to mold. Remove them promptly with clean tweezers, taking care not to disturb healthy roots.
Tips
Keep the design simple at first. A small number of compatible plants is easier to care for than a crowded arrangement. Choose plants with different heights or leaf shapes for visual interest, but give each one enough room to grow.
Think about access before planting. If the opening is narrow, placing plants and removing damaged leaves will be harder. A wide-mouth container is often more practical for a first terrarium, even if a narrow vessel looks decorative.
Use condensation as a clue, not a precise watering gauge. In a closed terrarium, a light mist on part of the glass can indicate moisture is circulating. Heavy, persistent condensation suggests too much moisture or too little ventilation. No visible condensation does not automatically mean the plants need water; check the soil and leaves as well.
Rotate the container occasionally if light reaches it more strongly from one side. This can help prevent plants from leaning in one direction. If the plants are growing quickly, trim them before leaves press against the glass, and remove all clippings afterward.
For a terrarium with no drainage hole, avoid adding water directly from a large can. A spoon or spray bottle gives you better control. Keep the water directed at the soil, and pause between small additions so you can see how quickly it is absorbed.
Troubleshooting
The glass is covered in heavy condensation. Open the lid for a while to release excess humidity, then check whether the soil is wet. Leave the lid off longer if the condensation returns quickly. Resume closed conditions only when the moisture level settles; avoid watering until the mix begins to dry.
The soil smells sour or looks soggy. This can signal excess water and poor airflow. Remove any standing water you can reach, take out dead plant material, and leave the container open to dry. If a plant has soft, dark, or mushy roots, remove it and trim away clearly damaged parts with a clean tool. Replant only if healthy roots remain, using fresh, suitable mix.
White fuzz appears on the soil or leaves. Remove the affected material and improve airflow by opening the container. Check for fallen leaves and reduce watering. A small amount of surface mold may be associated with persistently damp, poorly ventilated conditions; if it keeps returning or spreads, remove affected plants and refresh the setup rather than covering the growth.
Leaves turn pale, brown, or scorched. Move the terrarium away from direct sun and check whether the soil is too wet or too dry for that plant. Brown, crispy edges can have several causes, so assess light and moisture together rather than immediately adding water.
Plants wilt after planting. Some adjustment is possible after roots have been disturbed. Check that the roots are covered, the plant is not sitting in water, and the container has appropriate light. Do not respond to wilting with a large watering unless the soil is actually dry; excess moisture can worsen root stress.
A plant outgrows its space. Trim it with clean scissors if it responds well to pruning, or remove and replace it with a smaller plant. Do not let leaves remain pressed against wet glass, where they may stay damp and deteriorate.
Frequently Asked Questions
Does a terrarium need a drainage hole?
A drainage hole is helpful but not essential. Many decorative glass vessels have none, so water carefully and use a shallow optional stone layer only as a reservoir. It does not replace drainage, and excess water can still harm roots.
Should I keep the lid on all the time?
Not necessarily. A closed terrarium can retain humidity, but it may need occasional ventilation if condensation is heavy or mold appears. Open terrariums stay uncovered and suit plants that need drier air. Let the plants and moisture conditions guide you.
Can I put succulents in a closed terrarium?
Usually, that is a poor match. Closed terrariums hold humidity, while most succulents need their mix to dry between waterings and benefit from airflow. Use an open container and a freely draining mix for plants that prefer drier conditions.
How often should I water a terrarium?
There is no dependable universal schedule. The right interval depends on the plants, container, soil, light, and whether the lid is closed. Check the soil and plant condition before watering, and add small amounts rather than soaking the arrangement.
Where should I place my terrarium?
Choose a stable spot with bright, indirect light. Avoid direct sun and locations that become unusually hot or cold. If plants lean, fade, or scorch, reassess the light and move the container gradually to a more suitable place.
Can I use any houseplant in a terrarium?
No. Choose compact plants whose humidity, light, and watering preferences match the open or closed setup. Large, fast-growing plants and plants with very different care needs are difficult to maintain together in a small container.