Although planting a tree is typically a simple process, invest a little extra time putting your tree into the ground if you have clay soil. Clay soil poses special problems for new tree roots because it lacks proper drainage. According to the University of Minnesota Cooperative Extension, compacted clay soil particles effectively suffocate tree roots by reducing the amount of available oxygen in the soil. This can drastically slow tree growth and damage its overall health. One of the key steps in planting a tree in clay soil is ensuring that topmost roots are slightly exposed so they have access to adequate oxygen.
Choose a hardy tree species such as ash, willow or silver maple capable of surviving and thriving in clay soil conditions. Select a planting location providing six to eight hours of sun each day. Make sure the planting location doesn't have any overhanging obstacles, such as power lines, which might interfere with canopy growth.
Measure the height and width of your tree's root ball. Dig a hole in the ground at least three times the width of the root ball's diameter to minimize deformed root. For instance, if the root ball is 8 inches wide, dig a hole at least 24 inches wide. Dig the hole to a depth that equals the height of the root ball.
Place your tree's root ball in the center of the planting hole. Tilt the tree gently and scoop loose topsoil under the root ball until the top edges of the topmost roots are slightly above the surface of the surrounding clay soil. Use the height of the root ball as a guide, raising the top of the root ball 1 inch above the surrounding soil for every 8 inches of root ball height. For example, if your tree's root ball is 12 inches tall, raise the top edge of the root ball 1½ inches above the surrounding soil.
Shovel the loose clay soil back into the planting hole around the tree roots. Break clods of clay soil into small chunks by slicing straight into the soil with your shovel. Level the soil with your shovel to ensure it is even with the surrounding soil. Gently pour 10 to 15 gallons of water into the soil immediately around the root ball to provide needed moisture for your tree.
Check your tree's leaf spread visually to determine the drip line (an imaginary circle on the ground that matches the circumference of the tree's outermost leaves). Turn the top 6 to 8 inches of soil within the drip line using a shovel or rototiller so tree roots can expand more easily. Sprinkle a 2-inch layer of mulch across the entire surface of the exposed soil, including the soil immediately around the top of the root ball.