Unfortunately, the fading of white flowers always is more noticeable than it is on any other color bloom. If this was a pink hydrangea you wouldn’t see the browning nearly as quickly as we do on white petals. But beyond that, there are two things that cause hydrangea flowers to brown quickly. The first is exposure to hot sun and the second is the frequent splashing of water on the flowers. If a hydrangea is in a place where the sun is hitting the flowers from 11 AM to 3 PM that flower will brown faster than those that are in shade during that time period. Secondly, if a sprinkler system or hose is hitting the flowers frequently, this will also cause the petals to go brown. So in order to keep any hydrangea bloom in great shape for a longer period of time plant it where it will be in shade during the hottest part of the day, and water it deeply every 5 to 7 days depending on temperature, only in the morning so that the foliage and flowers dry quickly during the day. If a hydrangea is watered for a long period of time every 5 to 7 days, and the area around the plants is mulched, the plants will be able to go without more irrigation which will keep the flowers in better shape.