Clumpy soil creates air pockets which will cause the roots to dry out and kill the trees.
The best time to start working your ground is the spring, 1 year before, the planting will happen
Till it again in the spring before we come out to plant the trees. DO NOT plant a crop where the trees are going to be planted. It will compete for moisture with the trees.
The ground should be worked 4” to 8” in depth.
Weeds need to be dealt with before we come out to plant and also before we lay the fabric down.
You need to work the ground around the trees to keep the soil loose and weed free for fabric installation.
The better that the site is worked up, the better the chance of the trees surviving.
Planting into sod is not recommended. It is more difficult to do and leaves the trees fighting with the grass for valuable moisture.