Hard clay soil is not the ideal planting bed and is usually amended before planting. Clay soil is not conducive to good water drainage and can often drown a tree or plant because it ends up just sitting in water. If you have an existing maple tree that was planted or grew in hard clay soil, you should try to amend the planting site to fix the problem for a long-term solution.
Remove the clay, if possible. Extend out to cover a radius that is two times as wide as the maple’s canopy. Get about two to three feet deep if you can without disturbing the roots, which will be mostly around the trunk of the tree.
Dig a “drainage chimney” with a post hole digger. Choose a spot just under the outer part of the canopy to dig a chimney about four to six feet into the ground. Measure from the bottom of the hole you just dug out in step one; however, if you could not do that step because there were too many roots, measure from the top of the soil and dig a chimney that is six to eight feet deep.
Fill the drainage chimney with pea gravel. This will allow much of the water to drain out rather than drowning your tree.
Fill the rest of the hole dug out in step one with a store purchased soil mix and compost.
Water the tree only when rain is scarce, especially on hot summer days. Water under the entire canopy, but don't get the leaves wet. Water slowly so that the soil is absorbing the water rather than allowing it to puddle on top. If you were unable to amend the soil as described above, than use only about an inch of water. For trees planted in clay soil, it is better to water the tree with less water more often.