A withered or dried up Tree in your backyard can only be revived by watering. To do this you will have to seek help from your Friends.

A 'Help Request' icon will be present above the withered Trees and Bushes. Simply tap on the Help icon and a request will be sent to your Friends.

A Tree can be revived only two times. After that you will have to chop down the tree in order to make way for new Tree to be planted.