The mixing device includes a mixing head (1) with an internal mixing chamber (2) into which an internal water supply passage (3) leads, that is designed to be connected to a pressurized water supply (4). An internal fertilizer supply passage (5a) is connected by a supply circuit (5) to a reservoir (7). An internal water distribution channel (8) to which fertilizer is added, is connected to a distribution hose (9). The mixing chamber includes a Venturi device so that flow of water across the mixing chamber from the water supply passage to the distribution channel produces a negative pressure that suck in fertilizer so that it mixes with the water.
