Most people use a mechanical spreader to distribute lawn treatments to their property.  These come in two sorts - a Drop Spreader and a Rotary Spreader. Both of these models require that you fill a hopper with material and push the spreader over the lawn.  For most homeowners, the biggest problem is knowing how far the spreader is depositing the nutrients. 

With a drop spreader, the device will have an opening in the base of the hopper that runs the width of the hopper.  When a trigger is pulled, the slot cover is pulled back and the material runs through the opening onto the grass.  As you walk, pushing the spreader ahead of you, the material is spread across the lawn. 

The biggest problem with these spreaders is that for a large area of grass, you need to walk up and down numerous times. The swath of lawn fertilized for each run is limited to the width of the spreader, and probably no more than eighteen to twenty four inches.  The advantage is that when you have smaller areas, or areas close to walkways and flowerbeds, the chemicals are dropped right below the spreader and not onto surrounding areas.

With a rotary spreader, the material is placed into the hopper in the same way as for the drop spreader.  The prime difference is that the opening drops material onto a segmented dish, with only a small amount of material going into each segment. 

When you walk behind this device, the dish rotates and flings the material onto the surrounding areas, thus covering a much wider area than the drop spreader.  Getting even coverage with this type of machine is more difficult, so make sure that you know how far the material goes and adjust your aisles accordingly.

For both spreaders, it is recommended that you cover the lawn in one direction, spreading one half the fertilizer.  Then cover the lawn a second time but in the perpendicular direction, using the second half of the fertilizer. 

Adjust the settings on the spreaders according to the label on the bag so that you get the appropriate amount of material spread evenly on the lawn.