If a seedling rather than a graft may take years to reach flowering age.

No, you don't need to fertilize landscape trees.

Landscape trees may often have to be fertilized to perform fully same as any other kind of green plant. Nitrogen-deficient-looking trees (and shrubs) are very common in plantings where I live. Many are planted in glacial till that had the topsoil removed during development. Even many of the native trees and shrubs do not grow in bare mineral soil in the wild.

And competitive planting situations - such as one might encounter in a cultivated landscape - can deplete nutrients necessary for optimum growth, especially when the tree is still young and not fully established and without a wide spreading root system. Supplemental fertilization may often be necessary -- ideally after a soil test indicates a need or if the tree displays signs of a nutrient deficiency.