Trees don't normally get the nutrients they need to thrive. Deep root fertilization will help increase your trees health by giving it the nutrients it needs to grow, just like multivitamins. Most trees usually recycle their leaves and branches in nature. Most trees nowadays in the landscape have to compete with grass for water and nutrients. We rake up our leaves in fall but in nature leaves decompose and increase organic matter in the soil and promote healthy growth. It's something we call natural nutrient cycling but it generally doesn't happen in today's grassy jungle. I highly recommend deep root fertilization for all your trees and shrubs. It will greatly improve the health and vigor of them. Tree roots are generally within the top 6-12" of soil. We use a probe to put the fertilizer right where the roots can pick it up. Deep root fertilization also adds water to the soil and is done with a slow release fertilizer to help mimic nature by slowly releasing fertilizer over time. This will also help to prevent any fertilizer burn by adding too much fertilizer to the tree all at once.