Abstract: A fertilizer mixing device for sprinkler systems including a water inlet pipe having a water inlet, a first water outlet, and a second water outlet. The water inlet is in communication with an existing water source. A mixing chamber is adapted for holding a predetermined amount of fertilizer and water therein. The mixing chamber comprises a housing having a first opening therein for receiving the first water outlet of the water inlet pipe therein. The housing has a check valve disposed therein. The check valve includes an input pipe and an output pipe. A water outlet pipe is provided that has a first water inlet, a second water inlet, and a water outlet. The first water inlet is in communication with the second water outlet of the water inlet pipe. The second water inlet pipe is in communication with the output pipe of the check valve of the mixing chamber. The water outlet is connectable with an existing sprinkler system.