Often trees are too deep in the ground:
you should see a flare at the base.
If the trunk looks like a cylinder stuck in the ground, it's planted too deeply. If that's the case, just remove some soil from around the base. You can aerate the soil by removing plugs to get some oxygen in there.
If you have a large area that's been waterlogged, you can rent an aerator to do it. & you might use Howard Garrett's Sick Tree Treatment-
something like dried molasses, vinegar, cornmeal...
don't remember the formula, but you can find it on Dirtdoctor.com. Gingkos are beautiful trees;
I love the ones at the FW Botanic Gardens. Best luck! | 
