Pumice would make a good bottom layer for any plant that develops sprawling/invasive roots. Trees, shrubs, vines, mint, etc.. The pumice layer will prevent plants from becoming rootbound from a single long taproot, and force it to develop more divisions of fine feeder roots near the surface instead.
The strategies I show are more designed for creating bonsai trees.
Usually the more delicate/tender the plant, the more soft the soil should be. Especially herbs I am learning prefer rich organic soil.