Substrate recipes: the right mix for your build

Substrate is the foundation of your terrarium. Get it wrong and plants struggle from day one. Get it right and your build thrives for years.

The three base recipes

Recipe 1: Standard closed terrarium mix

Best for: Most closed jars with humidity-loving plants

• 50% peat-based potting soil
• 25% orchid bark (small grade)
• 15% perlite
• 10% worm castings

This drains well but holds moisture. The worm castings provide gentle, slow-release nutrients.

Recipe 2: Open terrarium / succulent mix

Best for: Open jars with succulents, cacti

• 40% cactus soil
• 30% perlite
• 20% coarse sand
• 10% worm castings (small amount)

Fast-draining. Succulents hate wet feet.

Recipe 3: Bioactive mix

Best for: Bioactive builds with cleanup crew

• 40% peat-based potting soil
• 20% orchid bark
• 15% worm castings
• 10% charcoal (horticultural grade)
• 10% sphagnum moss
• 5% leaf litter (dried, crushed)

Richer in organic matter to feed both plants and microfauna.

Layer-by-layer assembly

For any closed terrarium:

1. Drainage (1-2 inches): Lava rock, leca, or pebbles
2. Barrier (optional): Mesh, landscape fabric, or sphagnum
3. Substrate (2-3 inches): The recipe above
4. Hardscape: Driftwood, rocks
5. Plants and moss

The drainage layer matters most. Skip it and your roots sit in standing water.

Pre-moistening

Always pre-moisten substrate before adding to the jar:

1. Mix ingredients in a separate bowl
2. Add distilled water slowly
3. Mix until substrate holds together when squeezed but doesn’t drip
4. Too dry = won’t form; too wet = compaction

Common mistakes

Using garden soil

Garden soil compacts, brings pests, has unknown composition. Use bagged potting mix.

Too much substrate

More than 3 inches and you risk anaerobic conditions in the lower layers.

Skipping drainage

Roots sitting in water = root rot. Always have a drainage layer.

Wrong soil for the build

Cactus mix in a closed jar = soggy disaster. Regular mix for succulents = root rot. Match mix to build type.

Using fresh compost

Too nutrient-rich, will burn roots. Use worm castings instead (gentler).

DIY vs pre-mixed

DIY pros

• Cheaper in bulk
• Customizable
• You know exactly what’s in it

Pre-mixed pros (like “ABG mix”)

• Convenient
• Tested ratios
• Available online (Josh’s Frogs, The Bio Dude)

For beginners: start with pre-mixed. Move to DIY once you understand the principles.

When to replace

Most terrarium substrates last 3-5 years before needing replacement:

• Compaction (water no longer drains)
• Nutrient depletion (plants stop growing)
• Bad smell (anaerobic conditions)
• Visible fungus/mold that won’t go away

If your build is older than 5 years and showing decline, consider a rebuild.

Specialty additives

Activated charcoal

Skip the layer (see our charcoal guide). A tablespoon mixed INTO the substrate is fine.

Sphagnum moss

Useful as barrier layer or for moisture retention. Soak before using.

Vermiculite

Alternative to perlite, holds more water. Use for very small jars that dry fast.

Worm castings

Slow-release nutrients. Use sparingly (10-15% of mix max).

The cheat sheet

Build type	Mix	Drainage
Closed tropical	Standard recipe	Required
Open succulent	Cactus recipe	Required
Bioactive	Bioactive recipe	Required
Mounted plants	Sphagnum only	None

For the full build process, see our first closed terrarium guide.

Questions about your specific build? Ask in the Discord.