Regular mulching around tree bases protects the soil from weather, adds nutrients as the mulch breaks down, and encourages worms to aerate the soil. Applying liquid fertilizer in spring and fall ensures trees receive needed nutrients to grow healthy. While loosening soil with a pitchfork elsewhere in the yard, be careful not to damage surface roots within 3 feet of tree trunks. It is also important to have an annual tree inspection by an arborist to check for diseases, pests, or other problems that could harm trees.