DIY Terrarium: How to Build a Mini Indoor Garden in a Glass Jar

A terrarium is a miniature garden sealed or open inside a glass container. It’s one of the most charming craft projects you can make, and once built it requires almost no maintenance. This guide takes you through choosing the right container, selecting plants, layering the substrate, and caring for your terrarium long-term.

Open vs Closed Terrariums

The first decision is whether to make an open or closed terrarium. Each suits different plants and environments.

• Open terrarium: Has no lid or an incomplete seal. Allows air circulation and suits succulents, cacti, and air plants that prefer dry conditions.
• Closed terrarium: Sealed with a lid. Creates a humid micro-environment where moisture cycles within the container. Suits mosses, ferns, tropical plants, and humidity-loving species.

Choosing Your Container

Almost any clear glass container can become a terrarium. Popular choices include glass geometric terrariums, large apothecary jars, fish bowls, old fish tanks, large wine glasses, and even light bulbs. Clear glass is preferable to tinted glass because plants need light to photosynthesize.

The container should be clean and dry before you begin. Wash it thoroughly with warm soapy water, rinse well, and allow it to dry completely.

Materials You Will Need

• Glass container
• Activated charcoal granules (aquarium or terrarium grade)
• Small pebbles or gravel (for drainage layer)
• Sphagnum moss (optional, acts as a filter layer)
• Potting mix appropriate to your chosen plants
• Small plants (see plant selection below)
• Decorative elements: small stones, driftwood, figurines, crystals
• Long tweezers or chopsticks for placing items in narrow containers
• Small spray bottle

Layering Your Terrarium

Layering is crucial for plant health. Each layer serves a specific function:

1. Drainage layer (2-4cm): Add small pebbles or gravel to the base. This prevents roots from sitting in standing water, which causes root rot.
2. Charcoal layer (1cm): Sprinkle a thin layer of activated charcoal. Charcoal absorbs toxins and prevents the bacterial build-up that causes that “swamp smell” in closed terrariums.
3. Moss layer (optional): Place a thin layer of sphagnum moss above the charcoal. This acts as a barrier preventing soil from filtering down into the drainage layer.
4. Soil layer (5-8cm): Add your potting mix. The depth depends on the root systems of your plants. Most small terrarium plants need at least 5cm of soil. For succulents, use a cactus mix. For tropical plants, use a peat-based potting mix.

Plant Selection for Beginners

Choose small, slow-growing plants that suit your container’s light and humidity conditions.

For closed/humid terrariums:

• Fittonia (nerve plant) – colourful patterned leaves
• Miniature ferns
• Pilea peperomioides (money plant)
• Moss varieties
• Baby tears (Soleirolia)

For open/dry terrariums:

• Echeveria and other small succulents
• Haworthia
• Air plants (Tillandsia) – need no soil at all
• Small cacti

Planting Your Terrarium

1. Plan your layout before planting. Arrange your plants on top of the soil without removing them from their pots first. Consider height, colour, and texture contrast.
2. Create planting holes in the soil using your finger, a stick, or chopsticks.
3. Gently remove each plant from its nursery pot and shake off excess soil from the roots.
4. Place each plant in its hole and firm the soil around it gently. In a narrow container, use long tweezers to manoeuvre plants into position.
5. Add your decorative elements: nestle small stones, place driftwood pieces, tuck in any figurines or crystals.

Watering and Initial Care

After planting, mist lightly with a spray bottle. You want the soil to be moist but not soggy. For a closed terrarium, you should see light condensation on the glass walls when the lid is on. If condensation is very heavy and the glass is obscured, remove the lid for a few hours to let some moisture escape.

Water a closed terrarium very sparingly – often once a month or even less. Open terrariums with succulents may need watering every 2-3 weeks depending on your environment.

Placement and Light

Place your terrarium in bright indirect light. Direct sunlight through glass can create a greenhouse effect and cook your plants. North or east-facing windowsills are ideal for most terrarium plants. Avoid placing terrariums near radiators or heating vents.

For more nature-inspired craft projects, explore our DIY Crafts guides. You might also enjoy checking our Craft Tools and Guides section for essential equipment recommendations.