In the opening scene Grandpa, Luke and Kate are all at the kitchen table counting their savings that have been kept in the cookie jar. In a close shot it is more than obvious that the bills are not real money.
Kate wants a small square of ground next to the house to be cleared and tilled so she can plant tomatoes and other vegetables. The McCoy's are going to pay off their tractor that they use to plow their fields where they plant crops that they often sell. They would have no need an additional garden to plant vegetables given the fact that they are already doing that.
When Grandpa hides the money that he was supposed to have deposited in the bank he simply tilts the tree stump and places the can containing the money in the dirt underneath the stump. The stump is in no way rooted to the ground.