Ways to reduce garbage
Since SimCity 3000, when garbage was introduced, the mayor can choose to enact ordinances such as Industrial Waste Disposal Tax, Composting and Trash Presort to reduce garbage quantity and pollution generated and/or increase recyclable proportion of garbage. Such ordinances have an impact on the city's treasury proportionate to the city's size.
Zoning landfills provides a way to reduce garbage, however garbage tends to take a long time to disappear.
Building incinerators or Waste to Energy Plants
Reduces, but doesn't eliminate garbage.
Shipping it out of the city for a fee
The player can also ship garbage out to your neighbors for a fee.