Once you know what species you want, the next step is selecting an actual tree to plant. Not all specimens are equal! Trees in nurseries can be subject to neglect and abuse, resulting in trees that may fail to thrive, or even die. Take your time inspecting the choices at the nurseries.
Small is better. Small trees establish more quickly and grow faster than larger trees. They are also cheaper and easier to handle. We plant larger trees in the City Parks due to concerns about accidental damage or vandalism, but in a home setting you can choose a smaller specimen.
The health and shape of the root system is critical, yet it is hard to see. Ask the nursery to pull the root ball out of the pot so you can look at the roots. If there are a lot of roots circling around the outside of the root ball, these will need to be cut off to prevent problems later in the landscape.
The condition of the trunk and branches if important, too. Select trees with a single stem and small side branches. IT WILL NOT LOOK LIKE A MATURE TREE!! This is VERY IMPORTANT! Trees grow by adding new mass on top of old mass, so a young tree with a branch three feet above ground will become an old tree with that same branch still three feet above the ground. Inspect the trunk and branches for damaged and dead pieces – a few of these can be pruned out, but a lot of damage suggests neglect that may have caused more problems than you can easily see.