In agriculture the landscape-architect is concerned primarily with the relation of the plant te the soil. He considers carefully such questions as soil drainage and soil composition, from the physical and chemical point of view, to determine what plants are best adapted to each particular locality. This consideration is most essential in the planting of such species as the rhododendrons, which require that the soil contains no lime, but must possess the presence of humus. In soil drainage the landscape-architect is concerned chiefly with the draining of large areas for open lawns, leaving undrained spaces to be used for bogs and rock-gardens.
Agriculture is also concerned with soil cultivation, or the methods of caring for the planted areas in such a manner as to secure the best growth of plant materials. Another important interest included under the head of agriculture is plant pathology, under which come spraying and the control of insect pests.