Hickory Trees and soil and Pentas
Just moved to new location and in yard have several hickory trees. I have tried to plant and re-plant pentas under the hickory's but the pentas are not doing well. Pentas are not difficult to grow and I have grown them for many years. Away from the hickorys the pentas are flourishing in the yard. Even the pentas which are not directly under the canopy of the hickory trees but just close are not doing well. I am wondering about the PH level from the hickorys. Can the hickorys create a high or low PH level from all the leaves and nuts that have fallen?
Pentas like sun. My best guess is the simplest one - the shade cast by your hickory tress is keeping the pentas from getting the light that they need.
There's another less likely but not impossible cause. Hickory nut shells exude a small amount of a chemical called juglone. You can read about it here:
Juglone can be toxic to some plants. If the trees have been dropping nuts for years, there's a chance the juglone in the soil has reached a level that's toxic to your pentas.