An onion harvester is an agricultural implement which is used for harvesting the onion crop. The onions are removed from the ground with the help of a rotating roll. However, since onions are a very sensitive crop, the harvest should be done as gently as possible. Generally, moist soil is advantageous to the onion harvest because in dry ground the machine is supported by the discs, instead of wheels, and this damages the crop. When storing such onions there is the risk of blight which can jeopardise the quality of the entire crop. Therefore, to prevent damage to the onions, the tractor with the attached onion harvester needs to be very careful when harvesting.

The front wheels of the onion lifter determine the grubbing depth, on more modern devices, this can also be done by an automatic depth controller. To achieve optimum harvest results, the centre-line of the harvester axis should be located at the level of the underside of the deepest onion. A filter chain of onion-lifter harvested onions is transported on the rear of the machine to the edge of the field and is usually stored there for a while to dry.