The soil must have adequate drainage; otherwise, air may be excluded, and the more beneficial micro-organisms may be destroyed. Soils which have poor drainage are often sour and acid. It will be necessary to improve this acidity by applications of hydrated lime. Wet soils are cold ones, and this means that plant growth is severely retarded. The situation is even more critical in the northern, colder parts of the country. Waterlogged soils cause roots to rot and a combination of all these problems can produce complete failures in some gardens.