Idiom:  Money Doesn’t Grow on Trees; used as an
idiomatic phrase.

Example:  

“Alex had asked his father to buy him a new Ferrari sports
car as a high school graduation present so that he could drive himself to
college.  Unfortunately, Alex’s father
could not afford to buy him such an expensive present.  His father told him that money doesn’t grow on trees, and bought him a Toyota instead.”

Meaning: 
Money Doesn’t Grow on Trees means that
it is not so easy to earn money.  It can
also be used to mean that you should be careful about how much money you spend.  In this example, Alex’s father could not
afford to buy him an expensive car for college. 
In general, the kind of money needed to buy a Ferrari is not so easy to
obtain, so instead, Alex’s father bought him a much cheaper and more sensible
car.  This idiom can be used to give
people advice on how they spend their money. 
It can especially be used to convey the idea that money is not so easily
earned.  This idiom is used as a phrase in
this example.

This idiom is from the LSI book “The Idiom Advantage –
Fluency in Speaking and Listening,” which is used as the primary Idioms textbook
in LSI’s Advanced Conversation classes.

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