Planting trees in clay soil. Dig a hole. Dig it deeper. Deeper still. And wide. Wider. And you might want to dig the hole even deeper and sink some drainage tile filled with rock. The bottom of that would be 8 or so feet deep and the top be about 2 feet below grade in your planting hole. The planting hole should be amended. I like pine bark fines, cotton burr compost and mushroom compost. Of course composted cow manure.
Don't fill the bottom of any planting hole with rocks. Ever.
I am not familiar with your area or zone. I am in 5 B in NW Missouri. Here if you succeed in growing a Ginkgo to a foot or so in a pot it will usually make it in the ground. The same pretty much goes for White Dogwood. These have a tendency to die fairly easily in growth up to about 2 feet or so. I grow both of these and sell them at a farmers market.
Any tree planted in the ground should be protected from blasting summer sun in its first year.. This can be done by placing a wooden crate over them or standing on end to provide shade for part of the day. Mulch well in winter.
Newly planted trees should be watered often when it is hot and dry.
Early Fall is the best time to plant a tree. Don't do so in the middle of Summer unless you want to spend a huge amount of time caring for it. Early Spring is also good. Going into their first winter in the ground, be sure that trees are watered well and mulch with leaves to about 12 inches.
Good luck.
