Which environmental initiative focuses on waste reduction at Starbucks?

The focus of waste reduction at Starbucks is best represented by the "Waste Not" initiative. This initiative aims to minimize waste generated from Starbucks locations by implementing strategies that target the reduction of materials that end up in landfills. It encompasses various practices such as improving recycling systems, ensuring more responsible sourcing of materials, and finding innovative ways to repurpose waste.

While the "Grounds for Your Garden" program also addresses waste by encouraging customers to utilize coffee grounds for gardening, it is primarily about reusing a specific type of waste rather than a comprehensive waste reduction strategy aimed at the overall operations of Starbucks.

The other options, like the "Plant a Tree" campaign and the "Reduce, Reuse, Recycle" program, focus on related environmental efforts but do not specifically encapsulate the overall waste reduction initiative that Starbucks promotes through its "Waste Not" program. Therefore, although "Grounds for Your Garden" contributes to the conversation around waste, the broadest and most strategic initiative aimed at waste reduction is indeed "Waste Not."