Definition
This idiom is used to caution someone about being careful with their spending, as money is a limited resource.
"I want to buy the newest game console." "You better think carefully, money doesn't grow on trees."
I always tell my children 'money doesn't grow on trees' when I tell them they can't have everything they want.
"We need to cut back on our spending." "I know, money doesn't grow on trees after all."