Hydrangers are hardy shrubs grown for their delightful summer flowers in the garden. Plant growers try to convince us that they are equally good as house plants - they ARE NOT. Enjoy the plant for as long as it flowers in a pot and then transplant it into a border to give you many years of enjoymant.
Remember, depending on whether your soil is Lime or Acid, it will have pink flowers if Lime or blue if Acid. Look at local gardens to see what is growing. Heathers, Rhododendrons, Camelia, etc. shows the soil to be acid.
However, the soil or pot compost (can be changed to acid by watering with `Sequestrin` with resulting blue flowers. You can buy this from any garden centre.