A terrarium is a miniature garden enclosed in glass — part science experiment, part living art. They’re surprisingly easy to build, require almost no maintenance once established, and make fantastic conversation pieces. Here’s everything you need to build one this weekend.

Choosing Your Terrarium Type

Before gathering materials, decide which type you want to build. The choice affects everything from plant selection to long-term care.

Closed Terrariums

A sealed glass container creates its own water cycle. Moisture evaporates from the soil and plants, condenses on the glass, and drips back down. Once balanced, these can go months without any attention.

Best for: Tropical plants, ferns, mosses, fittonias

Open Terrariums

An open-top container allows air circulation and moisture to escape. These need occasional watering but offer more flexibility in plant choice.

Best for: Succulents, air plants, cacti, plants that prefer drier conditions

Materials You’ll Need

Gather everything before you start — building a terrarium is a quick project once materials are ready.

The Container

Any clear glass vessel works. Popular choices:

  • Mason jars (small, beginner-friendly)
  • Fish bowls (great for open terrariums)
  • Apothecary jars with lids (classic closed terrarium look)
  • Large glass cloches
  • Even old light bulbs for tiny terrariums

Key rule: No colored or frosted glass — plants need light to reach them.

Layering Materials

You’ll build your terrarium in layers, each serving a purpose:

  1. Drainage stones — Small pebbles or LECA (lightweight expanded clay aggregate). About 1-2 inches deep.
  2. Activated charcoal — A thin layer (1/4 inch) to filter water and prevent odors.
  3. Sphagnum moss (optional) — Acts as a barrier between the drainage layer and soil.
  4. Potting mix — Appropriate for your plants. Use cactus mix for succulents, regular potting mix for tropical plants.
  5. Decorative elements — Rocks, driftwood, figurines, colored sand — whatever tells your story.

Plants

For a closed terrarium, choose plants that love humidity:

  • Fittonia (nerve plant) — colorful veins, compact growth
  • Selaginella (spike moss) — lush, fern-like texture
  • Ferns (maidenhair, button fern) — classic terrarium plants
  • Peperomia — small varieties work beautifully
  • Sheet moss — the perfect living ground cover

For an open terrarium, go with drier-climate plants:

  • Small succulents — echeveria, haworthia
  • Air plants — no soil needed
  • Cacti — small varieties only

Building Your Terrarium: Step by Step

Step 1: Clean Your Container

Wash the glass inside and out with warm water. Any residue can encourage algae growth. Dry completely.

Step 2: Add the Drainage Layer

Pour 1-2 inches of pebbles or LECA into the bottom. This is critical — terrariums don’t have drainage holes, so this layer prevents roots from sitting in water.

Step 3: Add Activated Charcoal

Sprinkle a thin, even layer over the stones. This keeps the enclosed environment fresh by absorbing impurities and preventing bacterial growth.

Step 4: Add the Moss Barrier (Optional)

Lay a thin sheet of sphagnum moss over the charcoal. This prevents soil from sifting down into the drainage layer over time.

Step 5: Add Potting Mix

Add 2-3 inches of potting mix, depending on your container’s depth. Create a slight slope or landscape — flat terrariums look less natural.

Step 6: Plant

Start with the largest plant and work toward the smallest. Use a spoon or chopstick to dig small holes.

  • Remove plants from their nursery pots and gently shake off excess soil
  • Place in holes and firm the soil around the roots
  • Keep plants away from the glass walls to prevent leaf rot from condensation
  • Leave space between plants for growth

Step 7: Decorate

Add moss around the base of plants to cover bare soil. Place stones, small pieces of driftwood, or other decorative elements. This is where your terrarium becomes unique.

Step 8: Water Lightly

For a closed terrarium, mist lightly until the soil is damp but not soggy. Less is more — you can always add water, but removing excess is tricky.

For an open terrarium, water sparingly with a small watering can or squeeze bottle.

Step 9: Find the Right Spot

Place your terrarium in bright, indirect light. Direct sunlight through glass creates a greenhouse effect that can cook your plants. A spot near a window but out of direct sun beams is perfect.

Long-Term Care

Closed Terrariums

  • Condensation check: Some fogging on the glass is normal. If you can’t see through the glass, crack the lid for a few hours to let excess moisture escape.
  • Watering: Rarely needed. If the soil looks dry and there’s no condensation, add a small amount of water.
  • Pruning: Trim plants that outgrow the space. Remove any dead or yellowing leaves immediately.

Open Terrariums

  • Water every 1-2 weeks or when soil is dry
  • Watch for leggy growth — a sign of insufficient light
  • Rotate quarterly for even growth

Troubleshooting

Foggy glass that won’t clear: Too much moisture. Open the lid (or remove covering) for 24 hours.

Mold on soil surface: Usually from too much moisture and not enough airflow. Remove visible mold, reduce watering, and increase ventilation.

Yellowing leaves: Could be overwatering or too much direct sunlight. Adjust both and remove affected leaves.

Plants growing too tall: Prune regularly. In a closed terrarium, this is normal — the humid environment promotes growth. Trim and propagate the cuttings.

Get Creative

Once you’ve built your first basic terrarium, the possibilities are endless. Try themed terrariums with miniature figurines, create a desert landscape with succulents and sand, or build a moss garden in a vintage bottle. Each one is a tiny world you get to design from the ground up.