An automatic fertilizing apparatus (10) connected in series with a watering system (150) that includes a water source (152) and a sprinkler head(s) (158). The apparatus (10) consists of a liquid fertilizer container (12) having a water inlet port (20) and a water/fertilizer outlet port (24), and a fertilizing control assembly (50) having an outer fertilizer control tube (52) and an inner fertilizer control tube (82). The tube (52) which includes an outlet fertilizer entry slot (54) is inserted through the port (20) and the port (24) and is fixedly attached therethrough. The tube (82) is rotatably inserted into the tube (52) and includes an inner fertilizer entry slot (84), an inlet end (86) connected to the water source (152), an outlet end (88) connected to the sprinkler head(s) (158) and a vortex tube (87). The vortex tube (87) produces a partial vacuum that allows the fertilizer to be drawn into the two slots (54,84) and enter the water stream from the water source (152), through the two tubes (52,82) and out the sprinkler heads(s) (158).