This means that money is something that must be earned and that it is not easy to acquire it. It often means that you should be careful how much you spend, because money is not an infinite resource.
Money doesn’t grow on trees
With enough water and sunshine, a tree will grow strong roots to further sustain its growth, taking nutrients from the soil and needing no more help from a human to continue living. When a tree has matured, it will start to produce fruit, which can be gathered and enjoyed for free. Therefore, for very little personal effort, humans can enjoy the continuous offerings of fruit from a tree. On the other hand, money is not nearly as easy to obtain. You can't just walk up to a tree and gather cash from it like you would fruit – money requires considerable effort to earn, and some people, especially children, may not always understand that.

This idiom became widely used more than 100 years ago, emerging in writings near the end of the 1800s. For example, the Statesville Landmark newspaper from 1891, reads “Money doesn't grow on trees here yet."
Child:“Can I have ten pounds to go to the cinema?”
Parent:“Ten pounds?! That’s too expensive! Money doesn’t grow on trees you know!”

Mother:“If you want to buy a new Smartphone, you will need to find a job and save up for it. Money doesn’t grow on trees - you will appreciate something more if you have worked for it!”

"In the national elections the people have voted for higher wages and lower taxes, but they must realise that governmental money doesn’t grow on trees.
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