Plan Your Closed Terrarium Build

A healthy terrarium begins before any substrate enters the container. Planning prevents the most common mismatches: sun-loving plants in dim rooms, humidity-loving plants mixed with succulents, oversized plants in narrow jars, and too much water added to a container with nowhere for it to go.

Use this lesson to make four decisions: where the terrarium will live, which container fits that location, which plants can share its conditions, and how much material you need.

Start with the location

Choose a stable location before choosing plants. Observe it at several times of day.

Your ideal position has:

• Bright, indirect light for most of the day
• No direct midday or afternoon sun on the glass
• A steady room temperature between roughly 18–24°C
• Distance from radiators, air-conditioning vents, and exterior doors
• Enough clearance to remove the lid and inspect the plants

If you can comfortably read beside the location during the day without switching on a lamp, it may have enough ambient light. If the spot is dim, plan for a cool LED grow light on a timer rather than moving the terrarium into direct sun.

Choose a workable container

For a first build, choose a clear container between 3 and 10 liters with an opening at least as wide as your hand. Wide openings make planting, cleaning, and pruning much easier.

Measure:

1. The container's inside width
2. Its usable height below the lid
3. The width of the opening
4. The approximate volume

Reserve at least one quarter of the usable height for drainage and substrate. Plants should fit in the remaining space with several centimeters above and around their leaves.

Select compatible plants

Choose plants for the environment inside the container, not only for appearance. Closed terrariums suit compact tropical plants that prefer consistently humid air and damp—but aerated—soil.

A balanced three-plant palette might include:

• Structure: a small fern or upright pilea
• Mid-layer: fittonia or compact peperomia
• Ground layer: selaginella, moss, or a small creeping fig cutting

Check the mature size, not just the nursery size. Avoid combining plants with conflicting needs. Succulents, cacti, most herbs, and plants that need strong direct sun do not belong in a sealed tropical terrarium.

Sketch the planting layout

Draw the container as a simple rectangle or circle viewed from above. Mark the tallest plant toward the rear, the focal plant slightly off-center, and lower plants near the front. Leave visible substrate between them.

Plan for:

• A clear viewing side
• Space between leaves and glass
• Access for pruning tools
• A slight substrate slope for depth
• An open patch where you can inspect soil moisture

Do not design only for opening day. Imagine each plant at twice its current width.

Calculate materials

You do not need laboratory precision, but rough quantities prevent waste and overly deep layers.

For a medium 5-liter container, begin with:

• 1–1.5 liters of drainage material
• Enough separator material to cover the drainage layer once
• 2–3 liters of prepared substrate
• Two or three plants in 5–7 cm nursery pots
• One or two small handfuls of moss
• A starter culture of springtails, if available

Prepare extra substrate, but add it gradually. The final soil line should support roots without consuming the entire visible area.

Write your moisture plan

Decide how you will judge moisture before watering. Use visible signals:

• Substrate color and texture
• Condensation timing
• Leaf firmness
• Standing water in the drainage layer

Your first watering should moisten the root zones without filling the drainage layer. Write down the amount you add. That record gives you a baseline if the build looks too dry or too wet later.

Pre-build checklist

Before assembly, confirm:

• The container is washed, rinsed, and dry
• Plants are compatible with humidity and indirect light
• Every plant fits through the opening
• Roots and leaves are free of visible pests
• Substrate is moist but not dripping
• Tools can reach the bottom and back of the container
• The final location is ready

With those decisions made, continue to the detailed closed terrarium build guide, or return to the course overview to see the full learning path.