There is an old Chinese proverb that says in essence; the best time to plant a tree was twenty-five years ago and the second best time is now.
Before choosing a tree visit your regional arboretum to see the mature tree growing in the landscape.
I agree wholeheartedly with just one small qualification. Although trees can be planted almost all growing season; spring really isn’t the best time to plant your new tree. In the spring, trees are in the process of breaking dormancy and are exuberantly sending up new succulent growth. Naturally, they require a lot more energy and water, which is only intensified if they are newly planted or transplanted.
By early summer, trees take a break and their growth rate starts to slow down. When their growth rate slows down, so do their water requirements and with reasonable care (watering and mulch) a newly planted tree’s chances for survival will be much improved.
There are some trees, however, that are slower to root and need a full growing season. If you are planting birch, oak, magnolia, ginkgo, the American hornbeam, yellowwood or hemlock, it is best to get them into the ground early in the spring.