Pumice a porous, volcanic rock. It's frequently used in soil mixes to allow airflow around plant roots, increase the drainage speed and loosen heavy potting mixes. For this reason, pumice makes an especially useful soil additive when potting drought tolerant plants like succulents and cacti. Alternately, adding a decorative layer to the top of your pots makes for an attractive, minimalistic top-dressing.
Pumice is safe to use with all houseplants, and can simply be mixed into soil or other potting mediums as necessary. For a quick succulent/cactus soil blend, try mixing 50:50 soil to pumice.
Approximately 1 quart of pumice. Ships in a bag lined with PLA, a bioplastic made from corn.