Expanded Clay Pebbles for Mushroom Cultivation and Humidity Management Out-Grow's expanded clay pebbles are a versatile cultivation tool used by mushroom growers to improve aeration, drainage, and ambient humidity control within the growing environment. Made from natural clay fired at high temperatures, these lightweight, porous pebbles are pH neutral and chemically inert, making them a safe and reliable addition to a wide range of cultivation setups. Expanded clay pebbles are most commonly used in mushroom cultivation as a humidity tray substrate — lining the bottom of a growing chamber or humidity tray with a layer of water-saturated pebbles creates a passive evaporation system that maintains consistent ambient humidity without the risk of direct substrate oversaturation. They can also be used to improve drainage and aeration when mixed into casing layers or growing media. Unlike many substrate materials, expanded clay pebbles are fully reusable. Simply rinse, sterilize, and dry between grows for repeated use across multiple cultivation cycles, making them a cost effective and environmentally friendly choice. Each bag contains 8 quarts of high quality expanded clay pebbles, sufficient for outfitting multiple growing chambers or humidity trays simultaneously.
