I am trying to grow a bay hedge in my front garden. I planted 4 2 foot high plants last October and the have started growing new shoots this spring. However, the new shoots are covered in black spots and the plants are prone to insect infestation, which I have been trying to control with spray. The plants are also quite yellow generally and not very healthy looking. Could the black spot be due to poor drainage? The soil is not very deep in this area. Is it worth digging up the plants and adding something to improve the drainage before replanting? Any advice gratefully received!