Ability for water to drain soil
Drainage is the ability for soil or other growing medium to lose (drain) water.
Different plants require different drainage characteristics. For example, bog plants require little or no drainage, but desert plants typically require high drainage soils.
Drainage can be improved by adding coarse sand. Clays tend to restrict drainage. Humus will add a water retention ability.
For gardens and landscaped areas, drains (eg. French drains) may be added to improve drainage.
Use this tag for all drainage questions, whether they are for pot plants or larger landscape drainage questions.