Plants that have been growing for a season a planter with a pumice wick will grow vigorously, and the roots will ultimately extend right down into the pumice layer, but they DO NOT ROT!
This photograph shows one pumice wick at the end of the season. After the frost, this plant was pulled from a square planter. You can see that the roots have encased the pumice stones to the extent that the whole mass conforms to the square shape of the planter, and was pulled out as one piece. More importantly, the picture shows a season's growth of healthy roots, with no rot, lots of air, and no soil compaction.