Guide
Terrarium drainage: LECA vs gravel vs lava rock
The drainage layer catches spare water below the roots, so the soil never sits in it. What matters is how much space it leaves for water, how heavy it is, and whether it breaks down.
| Material | Holds water | Pore space | Weight | Breaks down in |
|---|---|---|---|---|
| Aquarium gravel | 7.5 % by volume | 40 % by volume | 1500 g/L | does not |
| Decomposed granite | 11.5 % by volume | 35 % by volume | 1650 g/L | does not |
| Fine clay pebbles | 16 % by volume | 80 % by volume | 400 g/L | does not |
| Lava rock (scoria) | 17.5 % by volume | 55 % by volume | 900 g/L | does not |
| LECA (expanded clay) | 14 % by volume | 80 % by volume | 380 g/L | does not |
| Pea gravel | 5 % by volume | 40 % by volume | 1450 g/L | does not |
| Perlite | 25 % by volume | 85 % by volume | 90 g/L | does not |
| Pumice | 27.5 % by volume | 74.5 % by volume | 560 g/L | does not |
| River pebbles | 3 % by volume | 40 % by volume | 1500 g/L | does not |
LECA is light and holds water in its pores, which helps a jar recover from overwatering; gravel is cheap and heavy; lava rock sits between the two. Any of them needs a barrier on top so soil does not wash down.
- 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.
More terrarium guides
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- 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 layers explainedDrainage, barrier, soil and top dressing, and what each does.
- 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.