Landscapers lay down mulch and pine straw for several different reasons. Mulch is made of organic materials like bark, wood chips, or leaves, and is spread over soil around your plants and trees to help your soil retain moisture, suppress weeds, regulate soil temperature, and improve soil fertility as it decomposes. In many ways, pine straw serves the same purpose. Both mulch and pine straw can also enhance the aesthetic appeal of your landscape by adding color and texture to your plant beds and borders.