Media depth and pore size affect the height of the perched water table which is created when water saturates media pore spaces. If coarse materials like gravel or sand are placed in the bottom of the container, the smaller pores in the media above this layer will retain water until pressure forces the liquid downward. Water accumulation above these coarse materials elevate the perched water table. Avoid media saturation in the upper or lower layers of the container by thoroughly mixing the media. Drainage, or hydraulic conductivity , is the rate at which water flows through the media.
Drainage is affected by the height of the container.
Containers that have identical heights but different diameters have similar drainage characteristics when the same media is used in both. In general, water retention of container media decreases as the height of the water column increases. Media in a tall container characterized by a greater depth drains more readily than the same media in a short container with a shallower media depth. When coarse material is placed at the bottom of a container, the height of the column is shortened, altering the drainage pattern. However, addition of coarse materials to the container bottom aids in drainage by constructing larger pore spaces.