Hello, one reason could be down to frost damage, and also lack of water through the summer whilst the flower buds are forming, has it been well watered recently? Is the foliage nice and healthy, and do you feed with an ericacious liquid feed through the growing season? i think next year you should be ok, but be cautious next winter and if we get a severe cold snap then wrap loosely with some fleece. julien

Many thanks for your help I will try what you have said next winter.
A lot of the leaves are a nice green but some of them have curled up and turn brown. joness