Select a well-shaped tree with good leaf color (if it has leaves). The parts—roots, trunk, branches—should be in good proportion so the tree looks balanced. There shouldn’t be signs of recent heavy pruning.
A well-formed root system is symmetrically branched, with the main root growing down and out to provide trunk support. Container-grown and balled-and-burlapped trees should have fibrous roots that are developed enough that the rootball retains its shape and holds together when removed from the container or when the ball is moved. The main roots should be free of kinks (sharp bends near the trunk) and circles (roots that wrap around the trunk).
A healthy trunk flares at the soil line. The absence of a flare may indicate a circling root. Brush away the soil from the top of the rootball, or stick your finger in the top 2 to 3 inches near the trunk. You can usually see or feel circling roots at the top of the rootball. A circling root is one that wraps all the way, or almost all the way, around the trunk. Over a few years, circling roots may girdle the trunk of the tree, slowing its growth and causing a weak spot that might break in a storm.
In general, select a tree with a straight, tapered trunk that can stand by itself. (Note, however, that some types of trees naturally have multiple or crooked trunks.) The trunk should bend evenly in the wind, like a fishing pole.
Nurseries frequently remove the lower branches and tie the trunk tightly to a stake. If you can find a tree with branches all the way to the ground, and that isn’t staked, or is tied to its stake loosely, it will grow into a better tree than a tightly-staked tree.
Untie the tree from its stake, and bend the top to one side. It should bend evenly along the trunk and return to within 20 to 30 degrees of vertical. If it doesn’t, look for a stronger tree.
Look for bark damage before buying. The bark should be free of injury from staking or improper handling. Avoid buying sunburned trees. Split, flattened, or dull-colored bark indicates sunburn. Sunburned trunks are extremely slow to heal and are subject to borer infestation.