Posted: 03/09/2014 at 15:01
Leave it till spring to prune them - I leave the faded flowers on mine all winter. Once you see emerging new buds on the stems below the flowers, cut off the dead flowers and dead flower stem down to just above them. (Here in London I did this in April, but it depends like so many other things on the weather and what spring is like where you are). This way you get some winter interest from the fading flowers, and they provide frost protection to the buds that will form flowers next year.
If you want to stop them getting too big, take out some of the oldest stems by cutting them right down to the ground. Cut some others back by a third and prune the remainder as I've suggested above - this will stimulate fresh stems to grow and these and the stems you cut back hard will not flower next year, but they will the year after and it stops the plant becoming too big and woody.
Other than that, they just need some compost - it doesn't have to be ericaceous but if they had blue flowers that will probably mean your soil is acid and ericaceous compost will help you get blue flowers again next year. If the soil is alkaline, they will be pink. Any compost is better than none! They need plenty of water, so if we have a dry spell in this promised Indian summer give them a drink and make sure they are well-watered when they start growing again in spring. They will drop most of their leaves over winter, this is normal, but if they are thirsty, they show it by drooping spectacularly!
Main thing is not to prune off too much or you will lose next year's flowers, but if they have got rather large, you might have to prune them drastically and lose the flowers for a year.
Hope this makes sense