Dogs are difficult to take care of还是to be taken care of?

前两个to take care of /to be taken care of 还有to plant /to be plant 都可以,后面的的通常都是to plant 因为句中出现了动作的实施者.
如果有具体语境的话,比如说We have twenty trees for them ...后边就必须用to be planted .如果动作是由自己完成就不必使用被动式.
其实就是看动作的实施者是不是说话的人.如果是让别人来做的话就得用被动式.再举个例子I've got some clothes to be washed .就可以暗示你是把衣服拿给别人去洗了