I'm not an expert, but my grandfather told me (years ago, obviously!) that normally hydrangea change from pink to blue due to there being aluminium in the soil, but if they have been there for some time, as you say yours have, then there are two other possible causes:1. you have used a fertilizer that is low in phosphorous and high in potassium, or2. you may have had building work carried out nearby, and the concrete and/or plasters used are leeching into the soilThere is of course one further option, and that is that the Fairies in your garden just prefer them that way! ;)Len
Hi LenThere has been so much building here since we moved in that it is very possible. Or....we gravelled the drive around them and that could be it....or there again it may be the fairiesxxx
Hi Shirley its to do with the soil this link tells you how to change themhttp://www.southernliving.com/home-garden/gardens/hydrangea-color-00417000078239/But then again who knows what those French Fairies get up to? in your garden.Hugs Lynn xxx
love your hydrangea!