Rhododendrons like acid soil so it may need watering with Sequestren an additive to increase acidity. You can also get Miracle Grow for acid soil too. Make sure it is potted in ericaceous soil. It all depend where you live, If you are in Cornwall it tends to be more acid and in the New Forest Rhodies flourish but there aren't many places in Wiltshire where they grow as the ground is mainly chalk(alkali) and not suitable. Try typing Ponticum Variegata into Google.