Definition - What does Drainage mean?
Drainage is the process in which water leaches downward from the upper soil layers to lower layers, or how surface water is removed.
Proper drainage is important because not all plants prefer moist conditions. In nature certain minerals such as sand provide rapid drainage, while heavy minerals like clay can restrict drainage. For container or potted plants drainage is facilitated by holes in the bottom of the pot.
MaximumYield explains Drainage
Poor drainage is easily spotted in areas where water tends to pool following a rainstorm.
Drainage can be improved by adding compost or sand. Potting soil is formulated for adequate seepage of water through the addition of perlite or vermiculite.
Some plants are said to prefer “wet feet,” which means that they are able to survive extended periods of moist conditions. Rain gardens are an example of gardens that can tolerate poor drainage.
Succulents on the other hand, thrive in more arid climates and soils, and therefore require a lighter, better drained medium such as sand.
Where proper drainage cannot be achieved through natural means, corrugated piping called tiling may be installed below the growing surface to move moisture away from the plant's roots.