An irrigation system for plants comprises at least one elongate plant through a main pipe with a first, greater cross-sectional area, a plurality of openings distributed in the longitudinal direction and positioned in the bottom of the plant trough, and a plurality of branch pipes each with a second, smaller cross-sectional area. The branch pipes connect the main pipe to the openings. The main pipe is further connected to means for supply and discharge of water. The water level in the plant trough is regulated by supplying or discharging water to and from the main pipe. In manufacture, the means are arranged on a frame belonging to a cultivation table.