Keep the sweetgum seedlings in their nursery containers under partial shade during the first summer, watering to a depth of two inches. Over the winter, move into full sun. In the spring, transplant the sweetgum trees into the garden, using mildly acidic heavy mulch and watering well over the summer.
The seedlings need watering weekly during the summer, but only water them during the winter if the weather is dry for longer than two weeks. The soil temperature should be 60 degrees Fahrenheit or higher before transplanting the trees into the garden in the spring. If transplanting multiple trees, space them at least 25 feet apart.