Building a terrarium is a great way to bring a bit of green into a small space. The key to success is choosing the right plants — ones that thrive in the humid, enclosed environment. This guide walks you through the best plant choices and how to set them up for long-term health.
What You’ll Need
- A glass container (open or closed, depending on the plants you choose)
- Small pebbles or gravel for drainage
- Activated charcoal (to keep the air fresh)
- Potting soil (preferably a well-draining mix)
- Small plants or cuttings (see step 1 for suggestions)
- Long tweezers or chopsticks (for planting in tight spaces)
- A spray bottle for watering
- Optional: decorative stones, moss, or small figurines
Step-by-Step
- Choose your plants. For a closed terrarium (with a lid), pick moisture-loving plants like ferns, mosses, and small tropical species. For an open terrarium (no lid), choose plants that prefer drier conditions, such as succulents and air plants. Good general choices include: Fittonia (nerve plant), Pilea (aluminum plant), Pteris (brake fern), Selaginella (spike moss), and various peperomias. Succulents like Haworthia and Echeveria work well in open containers.
- Prepare the container. Clean the glass thoroughly with warm, soapy water and rinse well. Make sure it is completely dry before you start.
- Add the drainage layer. Spread a layer of small pebbles or gravel about an inch deep at the bottom. This prevents water from pooling around the roots.
- Add a charcoal layer. Sprinkle a thin layer of activated charcoal over the pebbles. This helps filter the air and prevents mold and mildew in a closed terrarium.
- Add the soil. On top of the charcoal, add a layer of potting soil. For most terrarium plants, a depth of about two to three inches works well. If you’re using succulents, mix in some coarse sand or perlite to improve drainage.
- Plant your greenery. Use your fingers or long tweezers to make small holes in the soil. Gently place each plant’s roots into the hole and firm the soil around them. Space plants so they have a little room to grow, but they can touch slightly for a full look.
- Add finishing touches. Place moss over the soil surface to retain moisture and give a natural look. Decorative stones or small pieces of driftwood can add interest.
- Water lightly. Use a spray bottle to mist the soil and plants. For a closed terrarium, you want the soil to be moist but not soggy — you should see condensation on the glass but no standing water at the bottom. For an open terrarium, water just enough to dampen the soil.
- Place in suitable light. Most terrarium plants prefer bright, indirect light — near a north or east window is ideal. Avoid direct sunlight, which can overheat the glass and cook the plants.
Common Mistakes
- Overwatering: The most common issue. In a closed terrarium, water rarely escapes, so the soil stays wet. Always err on the dry side; you can add more water later, but you can’t easily remove it.
- Too much direct sun: Sun through glass can magnify heat and burn leaves. Keep the terrarium out of harsh afternoon sun.
- Using plants that grow too large: Regular houseplants like pothos or philodendron will quickly outgrow a small terrarium. Stick to slow-growing, compact species.
- Mixing incompatible plants: Succulents need dry conditions, while ferns need constant moisture. Putting them together means one will suffer.
- Skipping the charcoal: Without it, closed terrariums can develop a sour smell from stagnant water.
Tips
- Choose plants that have similar light and water needs to keep your terrarium balanced.
- Use a long-spouted watering can or spray bottle to water precisely without disturbing the soil.
- Trim plants regularly to keep them small and encourage bushier growth.
- If you’re a beginner, start with a hardy plant like a spider plant or a small fern.
- For a closed terrarium, open the lid occasionally to let in fresh air and prevent excessive condensation.
- Use a layer of sphagnum moss between the charcoal and soil to prevent soil from sifting down into the drainage layer.
Troubleshooting
- Mold on the soil or glass: This usually means there’s too much moisture. Remove the lid (if closed) and let it air out for a few hours. Wipe the glass with a paper towel. If mold persists, repot with fresh soil and reduce watering.
- Yellowing leaves: Often a sign of overwatering or poor drainage. Check that the drainage layer isn’t blocked and that the soil isn’t soggy. Let the soil dry out a bit before watering again.
- Leggy or stretched growth: The plant isn’t getting enough light. Move the terrarium to a brighter spot, but still avoid direct sun.
- Leaves turning brown or crispy: This could be from too much direct sun or low humidity. Move to a shadier spot and mist the plant if it’s in an open terrarium.
- Condensation that never clears: In a closed terrarium, a little condensation is normal, but if it’s constantly foggy, there’s excess water. Leave the lid off for a few hours to let it dry out.
- Plant rotting at the base: Remove the affected plant immediately to prevent spread. Check that the drainage layer is working and that the soil isn’t waterlogged.
Frequently Asked Questions
Can I use any glass container?
Yes, as long as it’s clean and has an opening large enough to plant through. Mason jars, fishbowls, and apothecary jars all work well.
How often should I water a terrarium?
There’s no set schedule. Check the soil moisture — if it feels dry to the touch, water lightly. In a closed terrarium, you might only need to water every few weeks.
Why is my closed terrarium fogging up?
That’s normal — it’s the water cycle in action. If the fog never clears, there’s too much water. Open the lid to let it dry out.
Can I put succulents in a closed terrarium?
It’s not recommended. Succulents need dry air and good airflow; a closed terrarium traps humidity and will likely cause rot.
Do I need to fertilize terrarium plants?
Generally, no. Terrarium plants grow slowly and don’t need much food. If you do fertilize, use a very diluted liquid fertilizer at half strength, and only during the growing season.
How long will my terrarium last?
With proper care, a terrarium can last for years. Plants may eventually outgrow the container, but you can prune them or replace them as needed.
Good Plants for a Terrarium: A Practical Guide