Trees planted in spring have a lot of pressure on them: They need to grow new leaves and new roots, all at the same time.
Photosynthesis and root development require sugar reserves that are generally stored in the roots, which means spring-planted trees go into these challenges as soon as they hit the ground.
Trees planted in fall, however, get to enjoy the milder weather with none of the pressures of growing up too fast. They can focus their energy on growing more roots, rather than growing new foliage.
In spring, we’re anxiously waiting for the ground to thaw and the soil to be “workable” before we can finally get out in the garden and start planting.
But in fall? The soil is actually warmer then than in spring. That’s because it’s been warmed up all summer long and stays warm—long enough for a tree to establish roots and absorb nutrients before it goes dormant.