The primary components of a fertilizer spreader are the hopper, the gauge and the flow lever. The hopper is the bin holding the fertilizer, with holes on the bottom to distribute the material. The gauge controls the size of the holes, while the flow lever opens and closes them.
Depending on the type of spreader, fertilizer can be distributed in two ways. Drop spreaders simply drop the hopper's contents, depositing a swathe of material the width of the spreader as it is pushed along. They are best for smaller yards and precision gardening. Broadcast spreaders, preferred for large areas, have a gear in the wheels that turns a spinning plate in the hopper, catching the fertilizer and tossing it in a broad spray in front of the spreader.