Q: I planted three hydrangeas last year. One is thriving but the other two not so much. They are all planted in the same area with similar soil and mulched with pine straw. Can you advise as to why one looks great and the others don’t?
A: When I investigate identical plants that have been planted and maintained similarly but which have grown differently, my work almost always points to root expansion problems.
Perhaps one had roots circling tightly in the pot which were not straightened and spread out at planting. This plant will never look as good as one with a better root system.
Perhaps one is in a spot with more clay in the soil, causing roots to have difficulty growing outward.
Perhaps one is getting excess water from a leaky gutter.
Since yours are still young, it is well within reason to take the weak ones up when the leaves have dropped this fall and redo the roots and planting area.
My bet is they will grow much better next year.