I'll disagree with woodweasels posting of the myth. I tried an experiment on a landscape I installed years ago and planted a number of shads. They came almost bare root so I tried the Fertilome Root Stimulator on a few, hoping it would help them along. About two months later, it was obvious which ones got the stimulator and which did not. I even asked someone to identify the "healthy" trees and all of them came back as the ones that got the product. My opinion from experience says it works and at the very least, it can't hurt. Keep the tree watered and let it get over the shock of transplanting. BTW, ever seen a large oak in the nursery with a 4' taproot? No, you haven't and they live. Don't worry. Water it well and give it a month before you give up. And don't be shy about the root stimulator.