Poor yields on blueberry plants

Hello,

i have about a 8 good sized blueberry plants In 40cm square pots (ericaceous compost)

I have had them about 3-5 years. All are looking healthy and put on a lot of growth last year. Most fruited pretty well last year.

Most fruited pretty well last year but this year the number of fruit per bush is not great. I think some may be due to the late frost but also none of them had a vast amount of flowers on them.

is there anything I can do to encourage them to fruit better next year. Maybe I gave them too much food last year?

one especially, called pink lemonade fruited brilliantly 2 years ago but since has had almost no fruit on it. Though it looks very healthy. 

Any tips would be greatly appreciated.

thanks

alex