1. The best time to plant a new tree is spring or fall. In summer, new trees are prone to dehydration.
2. Your hole should be at least twice the size of the tree's root ball, and it's best to loosen the soil around the hole with a tiller.
3. You should break up the dirt around the rocks before placing the tree in the hole. When you've installed the tree, fill the hole halfway with soil and give it a thorough soaking.
4. It's a good idea to spread bark chips around the tree. These will help the environment to retain moisture and will discourage weeds.
Tips from The Home Depot