Guide

Terrarium layers explained

Bottom to top: drainage, a barrier, soil, then a top dressing. Each has one job, and getting the water right between them is most of what keeps a jar alive.

• Drainage (LECA or gravel): spare water collects here, away from the roots.
• Barrier mesh: stops soil washing down into the drainage.
• Soil (a mix like ABG): where roots live. Deep enough for them, usually 5 to 8 cm.
• Top dressing (moss, leaf litter, stones): looks good, holds damp, feeds the crew.
• Water so the soil is damp, never soggy. Standing water above the drainage rots roots.

What goes in each layer

Drainage

• Aquarium gravel, holds 7.5 % by volume water
• Decomposed granite, holds 11.5 % by volume water
• Fine clay pebbles, holds 16 % by volume water
• Lava rock (scoria), holds 17.5 % by volume water
• LECA (expanded clay), holds 14 % by volume water
• Pea gravel, holds 5 % by volume water
• Perlite, holds 25 % by volume water
• Pumice, holds 27.5 % by volume water
• River pebbles, holds 3 % by volume water

Barrier

• Substrate barrier mesh, holds 1 % by volume water

Filter

• Activated charcoal, holds 30 % by volume water
• Biochar, holds 37.5 % by volume water
• Horticultural charcoal, holds 25 % by volume water
• Sphagnum barrier layer, holds 70 % by volume water
• Zeolite, holds 30 % by volume water

Soil

• ABG mix, holds 45 % by volume water
• Akadama, holds 37.5 % by volume water
• Aquasoil, holds 40 % by volume water
• Bagged potting soil, holds 60 % by volume water
• Calcined clay, holds 35 % by volume water
• Clay, holds 45 % by volume water
• Coco coir, holds 70 % by volume water
• Coco husk chips, holds 27.5 % by volume water
• Horticultural sand, holds 10 % by volume water
• Orchid bark (fir/pine bark), holds 30 % by volume water
• Peat-based soilless mix, holds 57.5 % by volume water
• Pine bark fines, holds 37.5 % by volume water
• Rice hulls, holds 20 % by volume water
• Sphagnum peat moss, holds 65 % by volume water
• Topsoil, holds 32.5 % by volume water
• Tree fern fibre, holds 35 % by volume water
• Vermiculite, holds 47.5 % by volume water
• Worm castings, holds 52.5 % by volume water

Top dressing

• Aquarium sand, holds 25 % by volume water
• Black sand, holds 23 % by volume water
• Cork crumbs, holds 15 % by volume water
• Dried long-fibre sphagnum moss, holds 55 % by volume water
• Leaf litter, holds 35 % by volume water
• Live sphagnum moss, holds 65 % by volume water
• Magnolia leaves, holds 32.5 % by volume water
• Oak leaf litter, holds 37.5 % by volume water

How water moves between them

• Layers go in damp, at about three quarters of what they hold.
• Gravel, LECA or lava rock under the soil catches excess water below the roots.
• Water wicks up from a wet drainage layer, and sideways into drier soil.
• When water rises into the root zone, roots start to rot.
• An as-needed watering tops the soil back up to 92% and no further.

Wilting point

30% of capacity

Root zone

3.5 cm

Wicking up peat or coir

4.5 cm

Sideways spread

20% of the gap a day

Compare the drainage materials in LECA vs gravel vs lava rock.

Pour the layers in the simulator

More terrarium guides

• Closed vs open terrariumWhich to build, and which plants suit each.
• Best plants for a closed terrariumPlants that live sealed, easiest first.
• Best moss for a terrariumMosses for closed and open jars, and what they grow on.
• Terrarium drainage: LECA vs gravel vs lava rockEvery drainage material side by side.
• Mould in a terrariumWhy new jars fuzz, which mould matters, and how to stop it.
• Springtails vs isopodsThe cleanup crew compared: what each eats and where it lives.