Q: Last week you described some ways to make a wisteria bloom but you didn’t tell about what my grandfather used to do. Each fall, he would stand on his shovel blade and slice through the wisteria roots a foot away from the plant. It would bloom the next year every time.
A: Your grandfather was carrying on the tradition of stressing a plant to make it bloom. Hundreds of years ago, monks would beat the trunks of their apple trees with canes to make them produce more fruit.
Whether you chop the roots or wound the bark, a plant responds to damage by producing hormones that affect growth and fruiting. The biggest pecans I ever saw came from a tree that had been struck by lightning early one summer. That tree “knew” that it wasn’t long for this world so it poured all of its reproductive energy into its autumn crop of nuts. It was dead the following spring.