---
title: Calcined clay in a terrarium | Glass Jar Garden
description: Calcined clay: Hard-fired clay grit that holds water inside each grain and never packs down. In the jar it has holds water 35 % by volume, pore space 72.5 %...
url: https://glassjar.garden/guide/soils/calcined-clay/
---

Soils and layers

# Calcined clay

Hard-fired clay grit that holds water inside each grain and never packs down.

## What the simulation uses

- Holds water: 35 % by volume (Water it keeps after draining; the rest runs down to the drainage.)

- Pore space: 72.5 % by volume (Room for air and water between grains; low means roots suffocate when wet.)

- Weight: 600 g/L (How heavy a litre is.)

- pH: 6 to 7 pH (How acid it keeps the soil.)

- Mould risk: none (How much fresh food it gives white mould; high-risk soils fuzz over in the first weeks.)

- Nutrients: none (Plant food it brings.)

- Presses down to: 72 % of its loose depth (How far pressing can pack it, keeping its weight.)

## Description
Small fired granules that stay near neutral and carry no nutrients. Add them to a mix for lasting air pockets without drying it out.

Also called Turface, fired clay granules.

Estimated, where sources were thin: values estimated from hobby and horticultural references; not measured.

[Grow it in a jar](https://glassjar.garden/?guide=soils/calcined-clay)

[Black sand](https://glassjar.garden/guide/soils/black-sand/) · [Clay](https://glassjar.garden/guide/soils/clay/) · [All soils and layers](https://glassjar.garden/guide/soils/)