Why do growers use the old native root when grafting instead of planting something new?
Growers use the old native root because it has already survived the local climate and soil, making it a hardy, established rootstock. Its own fruit is often poor, so they cut off its trunk and graft in a superior hybrid, such as a paper-shell pecan, to get better fruit from a resilient base.
Les explains that this is the normal method of grafting, which is the direct opposite of the illustration in Romans 11. Under normal grafting, the old root is native to a particular area and has survived the climate and soil, though its fruit probably isn't all that good. Horticulturists then breed up a good hybrid—he gives the example of the pecan tree. They take the old natural pecan, cut off the original trunk, and graft in a hybrid with a big, nice soft shell, called a paper shell. That is the normal way, but Romans 11 presents the opposite: the beautiful tree is cast aside and a wild olive tree is grafted in. The wild olive produced no fruit and was worthless, like a bad weed.