Young oak in a pot
Three years ago when both my in-laws sadly passed away, I planted an oak in a container for the family, intending to eventually place it where their ashes are scattered. Last autumn, I potted it up into a larger container. It has been doing well overall, but this year it only developed leaves below the leader. The leader itself looks fine with buds on, but they did not develop into leaves. Can anyone kindly explain why this has happened?