“Money doesn’t grow on trees” (or, in a 19th century form,  “Money don’t grow on trees”) is an old financial proverb meaning that money isn’t made easily, simply available for the picking. The proverb is, perhaps, as old as paper money and is cited in print by at least 1819.
 
Variations include “If money doesn’t grow on trees, why do banks have branches?” (cited from about 1967) and “If money really did grow on trees, everyone’s favorite season would be fall” (cited from about 2009).
 
 
6 July 1819, Connecticut Courant (Hartford, CT), pg. 2, col. 3:
Money does not grow on trees; and I verily believe, if the philosopher’s stone which turns every thing into gold, could be found in every field, it would serve rather to increase the vices, follies and miseries of mankind.
(...)
GILES JOLTER, Jun.
 
17 July 1819, Boston (MA) Daily Advertiser, “From the Connecticut Courant,” pg. 1:
Money does not grow on trees; and I verily believe, if the philosopher’s stone which turns every thing into gold, could be found in every field, it would serve rather to increase the vices, follies and miseries of mankind.
   
18 March 1851, Boston (MA) Daily Atlas, Paris Correspondence, pg. 2:
When the bills come to the husbands, they, unreasonable things, grumble, and scold, and fret; “money don’t grow on trees,” they say, as if anybody, much less a Parisian woman, was such a goose as ever to entertain for second, so stupid an idea; or as if bread and blankets, or indeed anything but acorns and horse-chesnuts grew on trees! 
 
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Ruth Hall:
A domestic tale of the present time. With other tales.
By Fanny Fern (Sarah Payson Parton—ed.)
New York, NY: Mason Brothers
1855
Pg. 167:
“Well, tell her to keep on trying, and you must grow up quick, and earn something too; money don’t grow on trees, or bushes, did you know that?
 
16 April 1869, Leavenworth (KS) Bulletin, pg. 1:
“Money is scarce!” Yes, with you it is, and likely to remain so, scarce until you do something to earn it. Money don’t grow on trees. It must be earned, and it can only be earned by honest, industrious effort.
   
6 September 1873, Pomeroy’s Democrat (Chicago, IL), pg. 3:
It is a common thing to hear people remark they expected to find money grow on the trees when the (sic) came to Texas. I think that is verified here, or can be by a little energy on their part. 
 
13 October 1874, Cincinnati (OH) Daily Gazette, pg. 7:
Money don’t exactly grow on trees, but cotton does, which is very nearly the same thing.
 
27 February 1876, Sunday Times (Chicago, IL), pg. 9:
“My God! One dollar! Dost thou think that dollars grow on the trees?”
 
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Kavanaugh’s Juvenile Speaker for Very Little Boys and Girls:
Containing Short and Easily Learned Speeches and Dialogues, Expressly Adapted for School Celebrations, May-day Festivals and Other Children’s Entertainments
By Russell Kavanaugh
New York, NY: Dick & Fitzgerald
1877
Pg. 7:
Remember, if we fail to please,
Like money, brains don’t grow on trees.
   
17 July 1877, Macon (GA) Weekly Telegraph, “Travels in Cuba,” pg. 6:
But money does not grow on trees in Cuba.
 
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Youth on the Prow
By Lady Wood (Lady Emma Caroline Wood—ed.)
In Three Volumes
Vol. I
London: Chapman & Hall
1879
Pg. 164:
“In my country money does not grow on trees, to fall into one’s lap when the wind blows.”
 
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Spokane County As It Is.
By C. B. Carlisle
Second Edition
Portland, OR: Steam Presses of Himes the Printer
1883
Pg. 16:
In this region money don’t grow on trees, and most honest people get it only by the sweat of the brow, still there’s enough filthy lucre in these parts to supply a moderate amount of it to every industrious, energetic person who is rightly anxious to work without being too particular as to the kind of work.
 
11 December 1883, Macon (GA) Weekly Telegraph, pg. 3:
THEY say money grows on trees in Texas, but returned emigrants say it takes hard climbing to get it.—Hartwell Sun. Money, or its equivalent, does grow on trees in Texas and Louisiana—pecan trees, for instance.
   
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Stray leaves from cousin Mabel’s sketch-book; or, Tolerance and intolerance
By Elizabeth Jane Whately
Published by , 1883
Pg. 22:
”... forthcoming when wanted,” rejoined Miss Lutwidge, “and besides money doesn’t grow on trees exactly, as you young ladies seem occasionally to think.”
 
15 March 1885, Macon (GA) Weekly Telegraph, pg. 5 ad:
We are satisfied with small profits and quick sales and that is the whole story boiled down and everybody knows from experience that money don’t grow on trees in these parts and consequently is one of the scarce luxuries, and therefore people have to trade where the almighty dollar will go the furthest and experience has proved to the trade that LYON & CLINE are the Leaders and Controllers of Low Prices.
(Lyons & Cline dry goods—ed.)
 
19 November 1891, The Landmark (Statesville, NC),  pg. 3, col. 6:
Money doesn’t grow on trees here yet.
 
12 April 1892, Omaha (NE) World Herald, pg. 1:
For a time money seemd to grow on trees for Stout. 
 
23 March 1893, Wilkes-Barre (PA) , pg. 4:
It (California—ed.) is not the Eldorado many think it is. Not a region where gold dollars grow on trees to be had for the picking.
 
13 May 1893, Morning Olympisn (WA), pg. 3:
Money don’t grow on trees here and the soft snaps were all gone long ago, but the man who comes west determined to get in and drill will succeed beyond his brightest expectations.—Chehalis Bee.
 
7 April 1895, Kansas City (MO)

, pg. 4:
That is a large sum of money, and worth looking after, especially in hard times when money doesn’t grow on trees.
 
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February 1896, Railway Herald Magazine, pg. 61:
Then as to the interest derived from invested money. Where does it come from? It doesn’t grow on trees, and it isn’t dug out of the ground.
 
14 May 1902, Nevada State Journal (Reno, NV), pg. 4, col. 2:
MONEY doesn’t grow on trees, but it seems to develop pretty rapidly in oil tanks.
 
17 July 1906, Washington (DC) Post:
Money doesn’t grow on trees.
 
27 March 1907, Grand Rapids (WI) Tribune, pg. 10, col. 3 ad:
Money Doesn’t Grow On Trees
(Centralia Hardware Company—ed.)