If you are not cursed/blessed with heavy clay soil, you can skip this entry.
I have mentioned the "clay pot effect" a few times on my blog. This is when you dig into clay soil an create a slick edge with the shovel that impaires the roots from growing. Once the slick edge hardens, the roots are unable to penetrate it. This will force the roots to turn back into themselves and the plant becomes rootbound. Either the roots eventually penetrate the hard edge in two to three years or the plant dies. It also hinders drainage around the plant and it can drown after heavy rains.
Today we went out to the orchard to dig holes for trees coming in this winter. We used a Bobcat with an 18 inch auger bit to drill out the holes. You easily get a large hole about 2-3 feet deep but it creates a very hard slick edge in the clay. To fix this problem, I use a fork to penetrate the slick surface and pop the soil out. You can use this same method when planting with a shovel in the backyard. Dig it out with a shovel first and then use a fork to pop the edges.
Wife in the Bobcat. She handles it like a pro.
Here is the hole with very slick hard edges. Digging with a shovel can create this same problem to a less extent. The shade is making it hard to really see how bad it really is.
Buy a really good fork for this job. None of the cheapo forks will last long if you have a lot of holes to pop.
The end result is a hole with rough edges that allow roots to more easily penetrate into the outside soil. I only worked the top 18 inches of the hole and the bottom. Most of the roots will grow laterally in the top 14 inches of clay and slowly work down since the aeration of clay is so poor. In addition, there will also be a larger taproot that goes straight down on many of my fruit trees. It provides water to the tree in times of drought.