Do trees need mulch around them? When planting new trees on your property, adding a good layer of mulch around them can be very beneficial to their healthy growth. Mulching is the process of placing an organic or inorganic material under the dripline of a tree or plant. The best mulch for trees and shrubs is organic mulch such as nutshells, leaves, and woodchips since they decompose over time and become part of the soil. Using inorganic mulch like pulverised tires, rocks, and stones might also be good for protecting soil in crowded areas. However, rocks and other inorganic mulch aren’t ideal for tree mulching. They can compact the soil, heat up to high temperatures, and increase the pH level of the soil.