The necessity for good drainage for trees as well as for flowers is well illustrated by Californian experience. In many places the soft surface soil is only about a foot deep. Then there is "hard pan " about 14 or 15 feet, then gravel. If a hole for a tree is made two feet deep, the tree may as well stand in a bucket of water. Such trees die or get sick. But when a hole four inches wide is bored through the hard pan under the trees to the gravel, the trees thrive amazingly. They grow like magic.