4 years ago I had my backyard landscaped. The landscaper planted 10 Oak Leaf Hydrangea plants in the nature area. This area is both part/full sun. Up until this year they have been beautiful. We have had tons of rain the last few months and when the weather began to change I noticed that 7 of the plants leaves started to wither. The leaves are withered and the plant stems are completely brown now so I assume that they have died. The remaining 3 plants still have their leaves and are turning fall colors. I am very sad as I look out my back door. I am unsure what has killed the plants, and if it is possible that they will come back?