Talkback: In the pink
Your climbing hydrangea is probably Hydrangea anomala subsp. petiolaris, which only comes in white! No matter how you feed it you will not be able to change its colour. Do take a look at a relative called the Japanese Hydrangea Vine, Schizophragma hydrangeoides 'Roseum', as this has pink flowers. An image search on Google will show you.
Hydrangeas are hardy shrubs, but new shoots can be damaged by frost in early spring. Delay pruning until spring as the old stems provide some frost protection. Then keep a sheet of fleece handy to throw over it on cold nights if frost is forecast.